{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-91187", "assignerOrgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "state": "PUBLISHED", "assignerShortName": "EEF", "dateReserved": "2026-09-15T15:30:01.892Z", "datePublished": "2026-09-24T13:20:52.974Z", "dateUpdated": "2026-09-24T14:47:30.520Z"}, "containers": {"cna": {"affected": [{"collectionURL": "https://repo.hex.pm", "cpes": ["cpe:2.3:a:dashbit:nimble_zta:*:*:*:*:*:*:*:*"], "defaultStatus": "unaffected", "modules": ["'Elixir.NimbleZTA.Cloudflare'"], "packageName": "nimble_zta", "packageURL": "pkg:hex/nimble_zta", "product": "nimble_zta", "programFiles": ["lib/nimble_zta/cloudflare.ex"], "programRoutines": [{"name": "'Elixir.NimbleZTA.Cloudflare':authenticate/3"}, {"name": "'Elixir.NimbleZTA.Cloudflare':verify_token/2"}], "repo": "https://github.com/dashbitco/nimble_zta", "vendor": "dashbit", "versions": [{"lessThan": "0.1.3", "status": "affected", "version": "0.1.2", "versionType": "semver"}]}, {"collectionURL": "https://github.com", "cpes": ["cpe:2.3:a:dashbit:nimble_zta:*:*:*:*:*:*:*:*"], "defaultStatus": "unaffected", "modules": ["'Elixir.NimbleZTA.Cloudflare'"], "packageName": "dashbitco/nimble_zta", "packageURL": "pkg:github/dashbitco/nimble_zta", "product": "nimble_zta", "programFiles": ["lib/nimble_zta/cloudflare.ex"], "programRoutines": [{"name": "'Elixir.NimbleZTA.Cloudflare':authenticate/3"}, {"name": "'Elixir.NimbleZTA.Cloudflare':verify_token/2"}], "repo": "https://github.com/dashbitco/nimble_zta", "vendor": "dashbit", "versions": [{"lessThan": "6458fd18a5ba41166d4973214c519e98fe05b72d", "status": "affected", "version": "bc004b70985ae5763901baab3a4e204047899768", "versionType": "git"}]}], "configurations": [{"lang": "en", "supportingMedia": [{"base64": false, "type": "text/html", "value": "<p>The application must add <code>NimbleZTA.Cloudflare</code> to its supervision tree and authenticate requests through it.</p>"}, {"base64": false, "type": "text/markdown", "value": "The application must add `NimbleZTA.Cloudflare` to its supervision tree and authenticate requests through it."}], "value": "The application must add NimbleZTA.Cloudflare to its supervision tree and authenticate requests through it."}], "cpeApplicability": [{"nodes": [{"cpeMatch": [{"criteria": "cpe:2.3:a:dashbit:nimble_zta:*:*:*:*:*:*:*:*", "versionEndExcluding": "0.1.3", "versionStartIncluding": "0.1.2", "vulnerable": true}], "negate": false, "operator": "OR"}], "operator": "AND"}], "credits": [{"lang": "en", "type": "finder", "value": "Kazlu"}, {"lang": "en", "type": "remediation developer", "value": "Jos\u00e9 Valim / Dashbit"}, {"lang": "en", "type": "coordinator", "value": "Jonatan M\u00e4nnchen / EEF"}], "dateAssigned": "2026-09-24T09:09:36.000Z", "descriptions": [{"lang": "en", "supportingMedia": [{"base64": false, "type": "text/html", "value": "<p>Improper Verification of Cryptographic Signature vulnerability in dashbit nimble_zta allows an unauthenticated remote attacker to authenticate as an arbitrary Cloudflare service token. Applications using the Cloudflare Zero Trust authentication strategy are affected.</p>\n<p><code>verify_token/2</code> in <code>lib/nimble_zta/cloudflare.ex</code> matches the result of <code>JOSE.JWT.verify/2</code> against <code>{_, token, _s}</code>, which discards the boolean verification result and returns the decoded token after a failed signature check. The attacker sends a forged JWT in the <code>cf-access-jwt-assertion</code> header, carrying the expected <code>iss</code> claim and the seven service token claims. <code>verify_iss/2</code> reads the <code>iss</code> claim from the forged token, so it rejects nothing, and the service token path then returns those claims as the authenticated identity.</p>\n<p>This issue affects nimble_zta: from 0.1.2 before 0.1.3.</p>"}, {"base64": false, "type": "text/markdown", "value": "Improper Verification of Cryptographic Signature vulnerability in dashbit nimble_zta allows an unauthenticated remote attacker to authenticate as an arbitrary Cloudflare service token. Applications using the Cloudflare Zero Trust authentication strategy are affected.\n\n`verify_token/2` in `lib/nimble_zta/cloudflare.ex` matches the result of `JOSE.JWT.verify/2` against `{_, token, _s}`, which discards the boolean verification result and returns the decoded token after a failed signature check. The attacker sends a forged JWT in the `cf-access-jwt-assertion` header, carrying the expected `iss` claim and the seven service token claims. `verify_iss/2` reads the `iss` claim from the forged token, so it rejects nothing, and the service token path then returns those claims as the authenticated identity.\n\nThis issue affects nimble_zta: from 0.1.2 before 0.1.3."}], "value": "Improper Verification of Cryptographic Signature vulnerability in dashbit nimble_zta allows an unauthenticated remote attacker to authenticate as an arbitrary Cloudflare service token. Applications using the Cloudflare Zero Trust authentication strategy are affected.\n\nverify_token/2 in lib/nimble_zta/cloudflare.ex matches the result of JOSE.JWT.verify/2 against {_, token, _s}, which discards the boolean verification result and returns the decoded token after a failed signature check. The attacker sends a forged JWT in the cf-access-jwt-assertion header, carrying the expected iss claim and the seven service token claims. verify_iss/2 reads the iss claim from the forged token, so it rejects nothing, and the service token path then returns those claims as the authenticated identity.\n\nThis issue affects nimble_zta: from 0.1.2 before 0.1.3."}], "impacts": [{"capecId": "CAPEC-475", "descriptions": [{"lang": "en", "supportingMedia": [{"base64": false, "type": "text/html", "value": "<p>The attacker authenticates as an arbitrary Cloudflare service token without holding the Cloudflare signing key. The application receives the <code>client_id</code> and the claims of the forged token as the authenticated identity, so the attacker gets the access that the application grants to that service token.</p>"}, {"base64": false, "type": "text/markdown", "value": "The attacker authenticates as an arbitrary Cloudflare service token without holding the Cloudflare signing key. The application receives the `client_id` and the claims of the forged token as the authenticated identity, so the attacker gets the access that the application grants to that service token."}], "value": "The attacker authenticates as an arbitrary Cloudflare service token without holding the Cloudflare signing key. The application receives the client_id and the claims of the forged token as the authenticated identity, so the attacker gets the access that the application grants to that service token."}]}], "metrics": [{"cvssV4_0": {"Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "Safety": "NOT_DEFINED", "attackComplexity": "LOW", "attackRequirements": "NONE", "attackVector": "NETWORK", "baseScore": 9.3, "baseSeverity": "CRITICAL", "privilegesRequired": "NONE", "providerUrgency": "NOT_DEFINED", "subAvailabilityImpact": "NONE", "subConfidentialityImpact": "HIGH", "subIntegrityImpact": "HIGH", "userInteraction": "NONE", "valueDensity": "NOT_DEFINED", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:H/SI:H/SA:N", "version": "4.0", "vulnAvailabilityImpact": "NONE", "vulnConfidentialityImpact": "HIGH", "vulnIntegrityImpact": "NONE", "vulnerabilityResponseEffort": "NOT_DEFINED"}, "format": "CVSS", "scenarios": [{"lang": "en", "value": "GENERAL"}]}], "problemTypes": [{"descriptions": [{"cweId": "CWE-347", "description": "CWE-347 Improper Verification of Cryptographic Signature", "lang": "en", "type": "CWE"}]}], "providerMetadata": {"orgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "shortName": "EEF", "dateUpdated": "2026-09-24T13:20:52.974Z"}, "references": [{"name": "GitHub Advisory", "tags": ["related", "vendor-advisory"], "url": "https://github.com/dashbitco/nimble_zta/security/advisories/GHSA-rj24-g8cc-g7g2"}, {"name": "EEF CNA record for CVE-2026-91187", "tags": ["related"], "url": "https://cna.erlef.org/cves/CVE-2026-91187.html"}, {"name": "OSV record EEF-CVE-2026-91187", "tags": ["related"], "url": "https://osv.dev/vulnerability/EEF-CVE-2026-91187"}, {"name": "Introducing commit bc004b7 in dashbitco/nimble_zta", "tags": ["related"], "url": "https://github.com/dashbitco/nimble_zta/commit/bc004b70985ae5763901baab3a4e204047899768"}, {"name": "Fix commit 6458fd1 in dashbitco/nimble_zta", "tags": ["patch"], "url": "https://github.com/dashbitco/nimble_zta/commit/6458fd18a5ba41166d4973214c519e98fe05b72d"}], "source": {"discovery": "EXTERNAL"}, "title": "Improper Verification of Cryptographic Signature in dashbit nimble_zta Cloudflare strategy", "workarounds": [{"lang": "en", "supportingMedia": [{"base64": false, "type": "text/html", "value": "<p>Disable the Cloudflare authentication strategy.</p>\n<p>To keep the user identity strategy available, reject the service token requests yourself. Examine each request before you call <code>NimbleZTA.Cloudflare.authenticate/3</code>, and reject it if its JWT carries the <code>common_name</code> claim and the <code>type</code> claim.</p>"}, {"base64": false, "type": "text/markdown", "value": "Disable the Cloudflare authentication strategy.\n\nTo keep the user identity strategy available, reject the service token requests yourself. Examine each request before you call `NimbleZTA.Cloudflare.authenticate/3`, and reject it if its JWT carries the `common_name` claim and the `type` claim."}], "value": "Disable the Cloudflare authentication strategy.\n\nTo keep the user identity strategy available, reject the service token requests yourself. Examine each request before you call NimbleZTA.Cloudflare.authenticate/3, and reject it if its JWT carries the common_name claim and the type claim."}], "x_proofOfConcept": [{"lang": "en", "supportingMedia": [{"base64": false, "type": "text/html", "value": "<ol>\n<li>Build a JWT payload that carries the <code>aud</code>, <code>common_name</code>, <code>exp</code>, <code>iat</code>, <code>iss</code>, <code>sub</code> and <code>type</code> claims. Use the <code>iss</code> the application expects, set <code>exp</code> to a future timestamp, and set <code>common_name</code> to the service token to impersonate.</li>\n<li>Append any signature segment. The segment must be present, because <code>JOSE.JWT.verify/2</code> needs three segments to parse the token. The signature does not need to verify against the Cloudflare keys.</li>\n<li>Send a request to the application with the forged JWT in the <code>cf-access-jwt-assertion</code> header.</li>\n<li><code>NimbleZTA.Cloudflare.authenticate/3</code> returns the claims of the forged token as the authenticated identity, with the <code>strategy</code> field set to <code>service_token</code>.</li>\n</ol>"}, {"base64": false, "type": "text/markdown", "value": "1. Build a JWT payload that carries the `aud`, `common_name`, `exp`, `iat`, `iss`, `sub` and `type` claims. Use the `iss` the application expects, set `exp` to a future timestamp, and set `common_name` to the service token to impersonate.\n2. Append any signature segment. The segment must be present, because `JOSE.JWT.verify/2` needs three segments to parse the token. The signature does not need to verify against the Cloudflare keys.\n3. Send a request to the application with the forged JWT in the `cf-access-jwt-assertion` header.\n4. `NimbleZTA.Cloudflare.authenticate/3` returns the claims of the forged token as the authenticated identity, with the `strategy` field set to `service_token`."}], "value": "* Build a JWT payload that carries the aud, common_name, exp, iat, iss, sub and type claims. Use the iss the application expects, set exp to a future timestamp, and set common_name to the service token to impersonate.\n* Append any signature segment. The segment must be present, because JOSE.JWT.verify/2 needs three segments to parse the token. The signature does not need to verify against the Cloudflare keys.\n* Send a request to the application with the forged JWT in the cf-access-jwt-assertion header.\n* NimbleZTA.Cloudflare.authenticate/3 returns the claims of the forged token as the authenticated identity, with the strategy field set to service_token."}]}, "adp": [{"metrics": [{"other": {"type": "ssvc", "content": {"timestamp": "2026-09-24T14:43:06.738544Z", "id": "CVE-2026-91187", "options": [{"Exploitation": "none"}, {"Automatable": "yes"}, {"Technical Impact": "partial"}], "role": "CISA Coordinator", "version": "2.0.3"}}}], "title": "CISA ADP Vulnrichment", "providerMetadata": {"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-09-24T14:47:30.520Z"}}]}}

{"dataType": "CVE_RECORD", "containers": {"adp": [{"title": "CISA ADP Vulnrichment", "metrics": [{"other": {"type": "ssvc", "content": {"id": "CVE-2026-91187", "role": "CISA Coordinator", "options": [{"Exploitation": "none"}, {"Automatable": "yes"}, {"Technical Impact": "partial"}], "version": "2.0.3", "timestamp": "2026-09-24T14:43:06.738544Z"}}}], "providerMetadata": {"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-09-24T14:43:10.349Z"}}], "cna": {"title": "Improper Verification of Cryptographic Signature in dashbit nimble_zta Cloudflare strategy", "source": {"discovery": "EXTERNAL"}, "credits": [{"lang": "en", "type": "finder", "value": "Kazlu"}, {"lang": "en", "type": "remediation developer", "value": "Jos\u00e9 Valim / Dashbit"}, {"lang": "en", "type": "coordinator", "value": "Jonatan M\u00e4nnchen / EEF"}], "impacts": [{"capecId": "CAPEC-475", "descriptions": [{"lang": "en", "value": "The attacker authenticates as an arbitrary Cloudflare service token without holding the Cloudflare signing key. The application receives the client_id and the claims of the forged token as the authenticated identity, so the attacker gets the access that the application grants to that service token.", "supportingMedia": [{"type": "text/html", "value": "<p>The attacker authenticates as an arbitrary Cloudflare service token without holding the Cloudflare signing key. The application receives the <code>client_id</code> and the claims of the forged token as the authenticated identity, so the attacker gets the access that the application grants to that service token.</p>", "base64": false}, {"type": "text/markdown", "value": "The attacker authenticates as an arbitrary Cloudflare service token without holding the Cloudflare signing key. The application receives the `client_id` and the claims of the forged token as the authenticated identity, so the attacker gets the access that the application grants to that service token.", "base64": false}]}]}], "metrics": [{"format": "CVSS", "cvssV4_0": {"Safety": "NOT_DEFINED", "version": "4.0", "Recovery": "NOT_DEFINED", "baseScore": 9.3, "Automatable": "NOT_DEFINED", "attackVector": "NETWORK", "baseSeverity": "CRITICAL", "valueDensity": "NOT_DEFINED", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:H/SI:H/SA:N", "providerUrgency": "NOT_DEFINED", "userInteraction": "NONE", "attackComplexity": "LOW", "attackRequirements": "NONE", "privilegesRequired": "NONE", "subIntegrityImpact": "HIGH", "vulnIntegrityImpact": "NONE", "subAvailabilityImpact": "NONE", "vulnAvailabilityImpact": "NONE", "subConfidentialityImpact": "HIGH", "vulnConfidentialityImpact": "HIGH", "vulnerabilityResponseEffort": "NOT_DEFINED"}, "scenarios": [{"lang": "en", "value": "GENERAL"}]}], "affected": [{"cpes": ["cpe:2.3:a:dashbit:nimble_zta:*:*:*:*:*:*:*:*"], "repo": "https://github.com/dashbitco/nimble_zta", "vendor": "dashbit", "modules": ["'Elixir.NimbleZTA.Cloudflare'"], "product": "nimble_zta", "versions": [{"status": "affected", "version": "0.1.2", "lessThan": "0.1.3", "versionType": "semver"}], "packageURL": "pkg:hex/nimble_zta", "packageName": "nimble_zta", "programFiles": ["lib/nimble_zta/cloudflare.ex"], "collectionURL": "https://repo.hex.pm", "defaultStatus": "unaffected", "programRoutines": [{"name": "'Elixir.NimbleZTA.Cloudflare':authenticate/3"}, {"name": "'Elixir.NimbleZTA.Cloudflare':verify_token/2"}]}, {"cpes": ["cpe:2.3:a:dashbit:nimble_zta:*:*:*:*:*:*:*:*"], "repo": "https://github.com/dashbitco/nimble_zta", "vendor": "dashbit", "modules": ["'Elixir.NimbleZTA.Cloudflare'"], "product": "nimble_zta", "versions": [{"status": "affected", "version": "bc004b70985ae5763901baab3a4e204047899768", "lessThan": "6458fd18a5ba41166d4973214c519e98fe05b72d", "versionType": "git"}], "packageURL": "pkg:github/dashbitco/nimble_zta", "packageName": "dashbitco/nimble_zta", "programFiles": ["lib/nimble_zta/cloudflare.ex"], "collectionURL": "https://github.com", "defaultStatus": "unaffected", "programRoutines": [{"name": "'Elixir.NimbleZTA.Cloudflare':authenticate/3"}, {"name": "'Elixir.NimbleZTA.Cloudflare':verify_token/2"}]}], "references": [{"url": "https://github.com/dashbitco/nimble_zta/security/advisories/GHSA-rj24-g8cc-g7g2", "name": "GitHub Advisory", "tags": ["related", "vendor-advisory"]}, {"url": "https://cna.erlef.org/cves/CVE-2026-91187.html", "name": "EEF CNA record for CVE-2026-91187", "tags": ["related"]}, {"url": "https://osv.dev/vulnerability/EEF-CVE-2026-91187", "name": "OSV record EEF-CVE-2026-91187", "tags": ["related"]}, {"url": "https://github.com/dashbitco/nimble_zta/commit/bc004b70985ae5763901baab3a4e204047899768", "name": "Introducing commit bc004b7 in dashbitco/nimble_zta", "tags": ["related"]}, {"url": "https://github.com/dashbitco/nimble_zta/commit/6458fd18a5ba41166d4973214c519e98fe05b72d", "name": "Fix commit 6458fd1 in dashbitco/nimble_zta", "tags": ["patch"]}], "workarounds": [{"lang": "en", "value": "Disable the Cloudflare authentication strategy.\n\nTo keep the user identity strategy available, reject the service token requests yourself. Examine each request before you call NimbleZTA.Cloudflare.authenticate/3, and reject it if its JWT carries the common_name claim and the type claim.", "supportingMedia": [{"type": "text/html", "value": "<p>Disable the Cloudflare authentication strategy.</p>\n<p>To keep the user identity strategy available, reject the service token requests yourself. Examine each request before you call <code>NimbleZTA.Cloudflare.authenticate/3</code>, and reject it if its JWT carries the <code>common_name</code> claim and the <code>type</code> claim.</p>", "base64": false}, {"type": "text/markdown", "value": "Disable the Cloudflare authentication strategy.\n\nTo keep the user identity strategy available, reject the service token requests yourself. Examine each request before you call `NimbleZTA.Cloudflare.authenticate/3`, and reject it if its JWT carries the `common_name` claim and the `type` claim.", "base64": false}]}], "dateAssigned": "2026-09-24T09:09:36.000Z", "descriptions": [{"lang": "en", "value": "Improper Verification of Cryptographic Signature vulnerability in dashbit nimble_zta allows an unauthenticated remote attacker to authenticate as an arbitrary Cloudflare service token. Applications using the Cloudflare Zero Trust authentication strategy are affected.\n\nverify_token/2 in lib/nimble_zta/cloudflare.ex matches the result of JOSE.JWT.verify/2 against {_, token, _s}, which discards the boolean verification result and returns the decoded token after a failed signature check. The attacker sends a forged JWT in the cf-access-jwt-assertion header, carrying the expected iss claim and the seven service token claims. verify_iss/2 reads the iss claim from the forged token, so it rejects nothing, and the service token path then returns those claims as the authenticated identity.\n\nThis issue affects nimble_zta: from 0.1.2 before 0.1.3.", "supportingMedia": [{"type": "text/html", "value": "<p>Improper Verification of Cryptographic Signature vulnerability in dashbit nimble_zta allows an unauthenticated remote attacker to authenticate as an arbitrary Cloudflare service token. Applications using the Cloudflare Zero Trust authentication strategy are affected.</p>\n<p><code>verify_token/2</code> in <code>lib/nimble_zta/cloudflare.ex</code> matches the result of <code>JOSE.JWT.verify/2</code> against <code>{_, token, _s}</code>, which discards the boolean verification result and returns the decoded token after a failed signature check. The attacker sends a forged JWT in the <code>cf-access-jwt-assertion</code> header, carrying the expected <code>iss</code> claim and the seven service token claims. <code>verify_iss/2</code> reads the <code>iss</code> claim from the forged token, so it rejects nothing, and the service token path then returns those claims as the authenticated identity.</p>\n<p>This issue affects nimble_zta: from 0.1.2 before 0.1.3.</p>", "base64": false}, {"type": "text/markdown", "value": "Improper Verification of Cryptographic Signature vulnerability in dashbit nimble_zta allows an unauthenticated remote attacker to authenticate as an arbitrary Cloudflare service token. Applications using the Cloudflare Zero Trust authentication strategy are affected.\n\n`verify_token/2` in `lib/nimble_zta/cloudflare.ex` matches the result of `JOSE.JWT.verify/2` against `{_, token, _s}`, which discards the boolean verification result and returns the decoded token after a failed signature check. The attacker sends a forged JWT in the `cf-access-jwt-assertion` header, carrying the expected `iss` claim and the seven service token claims. `verify_iss/2` reads the `iss` claim from the forged token, so it rejects nothing, and the service token path then returns those claims as the authenticated identity.\n\nThis issue affects nimble_zta: from 0.1.2 before 0.1.3.", "base64": false}]}], "problemTypes": [{"descriptions": [{"lang": "en", "type": "CWE", "cweId": "CWE-347", "description": "CWE-347 Improper Verification of Cryptographic Signature"}]}], "configurations": [{"lang": "en", "value": "The application must add NimbleZTA.Cloudflare to its supervision tree and authenticate requests through it.", "supportingMedia": [{"type": "text/html", "value": "<p>The application must add <code>NimbleZTA.Cloudflare</code> to its supervision tree and authenticate requests through it.</p>", "base64": false}, {"type": "text/markdown", "value": "The application must add `NimbleZTA.Cloudflare` to its supervision tree and authenticate requests through it.", "base64": false}]}], "cpeApplicability": [{"nodes": [{"negate": false, "cpeMatch": [{"criteria": "cpe:2.3:a:dashbit:nimble_zta:*:*:*:*:*:*:*:*", "vulnerable": true, "versionEndExcluding": "0.1.3", "versionStartIncluding": "0.1.2"}], "operator": "OR"}], "operator": "AND"}], "providerMetadata": {"orgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "shortName": "EEF", "dateUpdated": "2026-09-24T13:20:52.974Z"}, "x_proofOfConcept": [{"lang": "en", "value": "* Build a JWT payload that carries the aud, common_name, exp, iat, iss, sub and type claims. Use the iss the application expects, set exp to a future timestamp, and set common_name to the service token to impersonate.\n* Append any signature segment. The segment must be present, because JOSE.JWT.verify/2 needs three segments to parse the token. The signature does not need to verify against the Cloudflare keys.\n* Send a request to the application with the forged JWT in the cf-access-jwt-assertion header.\n* NimbleZTA.Cloudflare.authenticate/3 returns the claims of the forged token as the authenticated identity, with the strategy field set to service_token.", "supportingMedia": [{"type": "text/html", "value": "<ol>\n<li>Build a JWT payload that carries the <code>aud</code>, <code>common_name</code>, <code>exp</code>, <code>iat</code>, <code>iss</code>, <code>sub</code> and <code>type</code> claims. Use the <code>iss</code> the application expects, set <code>exp</code> to a future timestamp, and set <code>common_name</code> to the service token to impersonate.</li>\n<li>Append any signature segment. The segment must be present, because <code>JOSE.JWT.verify/2</code> needs three segments to parse the token. The signature does not need to verify against the Cloudflare keys.</li>\n<li>Send a request to the application with the forged JWT in the <code>cf-access-jwt-assertion</code> header.</li>\n<li><code>NimbleZTA.Cloudflare.authenticate/3</code> returns the claims of the forged token as the authenticated identity, with the <code>strategy</code> field set to <code>service_token</code>.</li>\n</ol>", "base64": false}, {"type": "text/markdown", "value": "1. Build a JWT payload that carries the `aud`, `common_name`, `exp`, `iat`, `iss`, `sub` and `type` claims. Use the `iss` the application expects, set `exp` to a future timestamp, and set `common_name` to the service token to impersonate.\n2. Append any signature segment. The segment must be present, because `JOSE.JWT.verify/2` needs three segments to parse the token. The signature does not need to verify against the Cloudflare keys.\n3. Send a request to the application with the forged JWT in the `cf-access-jwt-assertion` header.\n4. `NimbleZTA.Cloudflare.authenticate/3` returns the claims of the forged token as the authenticated identity, with the `strategy` field set to `service_token`.", "base64": false}]}]}}, "cveMetadata": {"cveId": "CVE-2026-91187", "state": "PUBLISHED", "dateUpdated": "2026-09-24T14:47:30.520Z", "dateReserved": "2026-09-15T15:30:01.892Z", "assignerOrgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "datePublished": "2026-09-24T13:20:52.974Z", "assignerShortName": "EEF"}, "dataVersion": "5.2"}

{"affected": [{"affectedData": [{"collectionURL": "https://repo.hex.pm", "cpes": ["cpe:2.3:a:dashbit:nimble_zta:*:*:*:*:*:*:*:*"], "defaultStatus": "unaffected", "modules": ["'Elixir.NimbleZTA.Cloudflare'"], "packageName": "nimble_zta", "packageURL": "pkg:hex/nimble_zta", "product": "nimble_zta", "programFiles": ["lib/nimble_zta/cloudflare.ex"], "programRoutines": [{"name": "'Elixir.NimbleZTA.Cloudflare':authenticate/3"}, {"name": "'Elixir.NimbleZTA.Cloudflare':verify_token/2"}], "repo": "https://github.com/dashbitco/nimble_zta", "vendor": "dashbit", "versions": [{"lessThan": "0.1.3", "status": "affected", "version": "0.1.2", "versionType": "semver"}]}, {"collectionURL": "https://github.com", "cpes": ["cpe:2.3:a:dashbit:nimble_zta:*:*:*:*:*:*:*:*"], "defaultStatus": "unaffected", "modules": ["'Elixir.NimbleZTA.Cloudflare'"], "packageName": "dashbitco/nimble_zta", "packageURL": "pkg:github/dashbitco/nimble_zta", "product": "nimble_zta", "programFiles": ["lib/nimble_zta/cloudflare.ex"], "programRoutines": [{"name": "'Elixir.NimbleZTA.Cloudflare':authenticate/3"}, {"name": "'Elixir.NimbleZTA.Cloudflare':verify_token/2"}], "repo": "https://github.com/dashbitco/nimble_zta", "vendor": "dashbit", "versions": [{"lessThan": "6458fd18a5ba41166d4973214c519e98fe05b72d", "status": "affected", "version": "bc004b70985ae5763901baab3a4e204047899768", "versionType": "git"}]}], "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db"}], "cveTags": [], "descriptions": [{"lang": "en", "value": "Improper Verification of Cryptographic Signature vulnerability in dashbit nimble_zta allows an unauthenticated remote attacker to authenticate as an arbitrary Cloudflare service token. Applications using the Cloudflare Zero Trust authentication strategy are affected.\n\nverify_token/2 in lib/nimble_zta/cloudflare.ex matches the result of JOSE.JWT.verify/2 against {_, token, _s}, which discards the boolean verification result and returns the decoded token after a failed signature check. The attacker sends a forged JWT in the cf-access-jwt-assertion header, carrying the expected iss claim and the seven service token claims. verify_iss/2 reads the iss claim from the forged token, so it rejects nothing, and the service token path then returns those claims as the authenticated identity.\n\nThis issue affects nimble_zta: from 0.1.2 before 0.1.3."}], "id": "CVE-2026-91187", "lastModified": "2026-09-24T19:39:45.600", "metrics": {"cvssMetricV40": [{"cvssData": {"Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "Safety": "NOT_DEFINED", "attackComplexity": "LOW", "attackRequirements": "NONE", "attackVector": "NETWORK", "availabilityRequirement": "NOT_DEFINED", "baseScore": 9.3, "baseSeverity": "CRITICAL", "confidentialityRequirement": "NOT_DEFINED", "exploitMaturity": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "privilegesRequired": "NONE", "providerUrgency": "NOT_DEFINED", "subAvailabilityImpact": "NONE", "subConfidentialityImpact": "HIGH", "subIntegrityImpact": "HIGH", "userInteraction": "NONE", "valueDensity": "NOT_DEFINED", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:H/SI:H/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X", "version": "4.0", "vulnAvailabilityImpact": "NONE", "vulnConfidentialityImpact": "HIGH", "vulnIntegrityImpact": "NONE", "vulnerabilityResponseEffort": "NOT_DEFINED"}, "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "type": "Secondary"}], "ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-91187", "options": [{"exploitation": "none"}, {"automatable": "yes"}, {"technicalImpact": "partial"}], "role": "CISA Coordinator", "timestamp": "2026-09-24T14:43:06.738544Z", "version": "2.0.3"}}]}, "published": "2026-09-24T14:18:18.667", "references": [{"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "url": "https://cna.erlef.org/cves/CVE-2026-91187.html"}, {"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "url": "https://github.com/dashbitco/nimble_zta/commit/6458fd18a5ba41166d4973214c519e98fe05b72d"}, {"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "url": "https://github.com/dashbitco/nimble_zta/commit/bc004b70985ae5763901baab3a4e204047899768"}, {"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "url": "https://github.com/dashbitco/nimble_zta/security/advisories/GHSA-rj24-g8cc-g7g2"}, {"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "url": "https://osv.dev/vulnerability/EEF-CVE-2026-91187"}], "sourceIdentifier": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "vulnStatus": "Deferred", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-347"}], "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "type": "Secondary"}]}

{}