{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-39804", "assignerOrgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "state": "PUBLISHED", "assignerShortName": "EEF", "dateReserved": "2026-04-07T12:28:54.916Z", "datePublished": "2026-05-01T20:34:24.604Z", "dateUpdated": "2026-05-01T20:34:24.604Z"}, "containers": {"cna": {"affected": [{"collectionURL": "https://repo.hex.pm", "cpes": ["cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*"], "defaultStatus": "unaffected", "modules": ["'Elixir.Bandit.WebSocket.PerMessageDeflate'"], "packageName": "bandit", "packageURL": "pkg:hex/bandit", "product": "bandit", "programFiles": ["lib/bandit/websocket/permessage_deflate.ex"], "programRoutines": [{"name": "'Elixir.Bandit.WebSocket.PerMessageDeflate':inflate/2"}], "repo": "https://github.com/mtrudel/bandit", "vendor": "mtrudel", "versions": [{"lessThan": "1.11.0", "status": "affected", "version": "0.5.9", "versionType": "semver"}]}, {"collectionURL": "https://github.com", "cpes": ["cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*"], "defaultStatus": "unaffected", "modules": ["'Elixir.Bandit.WebSocket.PerMessageDeflate'"], "packageName": "mtrudel/bandit", "packageURL": "pkg:github/mtrudel/bandit", "product": "bandit", "programFiles": ["lib/bandit/websocket/permessage_deflate.ex"], "programRoutines": [{"name": "'Elixir.Bandit.WebSocket.PerMessageDeflate':inflate/2"}], "repo": "https://github.com/mtrudel/bandit", "vendor": "mtrudel", "versions": [{"lessThan": "1.11.0", "status": "affected", "version": "da4027cff7d2b80319e76fe7a32f84beceec490a", "versionType": "git"}]}], "configurations": [{"lang": "en", "supportingMedia": [{"base64": false, "type": "text/html", "value": "The vulnerability is only reachable when both of the following conditions are true:<ul><li>Bandit's server-level <tt>websocket_options.compress</tt> is enabled (it defaults to <tt>true</tt>).</li><li>The per-upgrade <tt>compress: true</tt> option is passed to <tt>WebSockAdapter.upgrade/4</tt> (it defaults to <tt>false</tt>; Phoenix's default is also <tt>false</tt>).</li></ul>Stock Phoenix and LiveView applications are not affected because <tt>compress: false</tt> is their default."}], "value": "The vulnerability is only reachable when both of the following conditions are true:\n- Bandit's server-level websocket_options.compress is enabled (it defaults to true).\n- The per-upgrade compress: true option is passed to WebSockAdapter.upgrade/4 (it defaults to false; Phoenix's default is also false).\n\nStock Phoenix and LiveView applications are not affected because compress: false is their default."}], "cpeApplicability": [{"nodes": [{"cpeMatch": [{"criteria": "cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*", "versionEndExcluding": "1.11.0", "versionStartIncluding": "0.5.9", "vulnerable": true}], "negate": false, "operator": "OR"}], "operator": "AND"}], "credits": [{"lang": "en", "type": "finder", "value": "Peter Ullrich"}], "descriptions": [{"lang": "en", "supportingMedia": [{"base64": false, "type": "text/html", "value": "Allocation of Resources Without Limits or Throttling vulnerability in mtrudel bandit allows unauthenticated remote denial of service via memory exhaustion when WebSocket permessage-deflate compression is enabled.<p><tt>'Elixir.Bandit.WebSocket.PerMessageDeflate':inflate/2</tt> in <tt>lib/bandit/websocket/permessage_deflate.ex</tt> calls <tt>:zlib.inflate/2</tt> with no output-size cap, then materializes the entire decompressed payload as a single binary via <tt>IO.iodata_to_binary/1</tt>. The <tt>websocket_options.max_frame_size</tt> option only bounds the on-the-wire (compressed) frame size, not the decompressed output. A high-ratio compressed frame (e.g. uniform data at ~1024:1 ratio) can stay well under any wire-size limit while forcing GiB-scale heap allocations in the connection process before any application code runs.</p><p>An unauthenticated attacker who can open a WebSocket connection can send a single such frame to exhaust the BEAM node's memory and trigger an OOM kill.</p><p>This vulnerability requires both Bandit's server-level <tt>websocket_options.compress</tt> and the per-upgrade <tt>compress: true</tt> option passed to <tt>WebSockAdapter.upgrade/4</tt> to be enabled. Stock Phoenix and LiveView applications are not affected as they default to <tt>compress: false</tt>.</p><p>This issue affects bandit: from 0.5.9 before 1.11.0.</p>"}], "value": "Allocation of Resources Without Limits or Throttling vulnerability in mtrudel bandit allows unauthenticated remote denial of service via memory exhaustion when WebSocket permessage-deflate compression is enabled.\n\n'Elixir.Bandit.WebSocket.PerMessageDeflate':inflate/2 in lib/bandit/websocket/permessage_deflate.ex calls :zlib.inflate/2 with no output-size cap, then materializes the entire decompressed payload as a single binary via IO.iodata_to_binary/1. The websocket_options.max_frame_size option only bounds the on-the-wire (compressed) frame size, not the decompressed output. A high-ratio compressed frame (e.g. uniform data at ~1024:1 ratio) can stay well under any wire-size limit while forcing GiB-scale heap allocations in the connection process before any application code runs.\n\nAn unauthenticated attacker who can open a WebSocket connection can send a single such frame to exhaust the BEAM node's memory and trigger an OOM kill.\n\nThis vulnerability requires both Bandit's server-level websocket_options.compress and the per-upgrade compress: true option passed to WebSockAdapter.upgrade/4 to be enabled. Stock Phoenix and LiveView applications are not affected as they default to compress: false.\n\nThis issue affects bandit: from 0.5.9 before 1.11.0."}], "impacts": [{"capecId": "CAPEC-130", "descriptions": [{"lang": "en", "value": "CAPEC-130 Excessive Allocation"}]}], "metrics": [{"cvssV4_0": {"attackComplexity": "LOW", "attackRequirements": "PRESENT", "attackVector": "NETWORK", "baseScore": 8.2, "baseSeverity": "HIGH", "privilegesRequired": "NONE", "subAvailabilityImpact": "NONE", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "userInteraction": "NONE", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N", "version": "4.0", "vulnAvailabilityImpact": "HIGH", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "NONE"}, "format": "CVSS", "scenarios": [{"lang": "en", "value": "GENERAL"}]}], "problemTypes": [{"descriptions": [{"cweId": "CWE-770", "description": "CWE-770 Allocation of Resources Without Limits or Throttling", "lang": "en", "type": "CWE"}]}], "providerMetadata": {"orgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "shortName": "EEF", "dateUpdated": "2026-05-01T20:34:24.604Z"}, "references": [{"tags": ["vendor-advisory", "related"], "url": "https://github.com/mtrudel/bandit/security/advisories/GHSA-frh3-6pv6-rc8j"}, {"tags": ["related"], "url": "https://cna.erlef.org/cves/CVE-2026-39804.html"}, {"tags": ["related"], "url": "https://osv.dev/vulnerability/EEF-CVE-2026-39804"}, {"tags": ["patch"], "url": "https://github.com/mtrudel/bandit/commit/8156921a51e684a951221da7bc30a70a022f722e"}], "source": {"discovery": "EXTERNAL"}, "title": "WebSocket permessage-deflate inflate has no output-size cap in bandit", "workarounds": [{"lang": "en", "supportingMedia": [{"base64": false, "type": "text/html", "value": "Do not pass <tt>compress: true</tt> to <tt>WebSockAdapter.upgrade/4</tt>. Omitting this option (or setting it to <tt>false</tt>) prevents permessage-deflate from being negotiated, so the inflate path is never reached."}], "value": "Do not pass compress: true to WebSockAdapter.upgrade/4. Omitting this option (or setting it to false) prevents permessage-deflate from being negotiated, so the inflate path is never reached."}], "x_generator": {"engine": "cvelib 1.8.0"}}}}

{}

{"cveTags": [], "descriptions": [{"lang": "en", "value": "Allocation of Resources Without Limits or Throttling vulnerability in mtrudel bandit allows unauthenticated remote denial of service via memory exhaustion when WebSocket permessage-deflate compression is enabled.\n\n'Elixir.Bandit.WebSocket.PerMessageDeflate':inflate/2 in lib/bandit/websocket/permessage_deflate.ex calls :zlib.inflate/2 with no output-size cap, then materializes the entire decompressed payload as a single binary via IO.iodata_to_binary/1. The websocket_options.max_frame_size option only bounds the on-the-wire (compressed) frame size, not the decompressed output. A high-ratio compressed frame (e.g. uniform data at ~1024:1 ratio) can stay well under any wire-size limit while forcing GiB-scale heap allocations in the connection process before any application code runs.\n\nAn unauthenticated attacker who can open a WebSocket connection can send a single such frame to exhaust the BEAM node's memory and trigger an OOM kill.\n\nThis vulnerability requires both Bandit's server-level websocket_options.compress and the per-upgrade compress: true option passed to WebSockAdapter.upgrade/4 to be enabled. Stock Phoenix and LiveView applications are not affected as they default to compress: false.\n\nThis issue affects bandit: from 0.5.9 before 1.11.0."}], "id": "CVE-2026-39804", "lastModified": "2026-05-01T21:16:16.853", "metrics": {"cvssMetricV40": [{"cvssData": {"Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "Safety": "NOT_DEFINED", "attackComplexity": "LOW", "attackRequirements": "PRESENT", "attackVector": "NETWORK", "availabilityRequirement": "NOT_DEFINED", "baseScore": 8.2, "baseSeverity": "HIGH", "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": "NONE", "subIntegrityImpact": "NONE", "userInteraction": "NONE", "valueDensity": "NOT_DEFINED", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/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": "HIGH", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "NONE", "vulnerabilityResponseEffort": "NOT_DEFINED"}, "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "type": "Secondary"}]}, "published": "2026-05-01T21:16:16.853", "references": [{"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "url": "https://cna.erlef.org/cves/CVE-2026-39804.html"}, {"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "url": "https://github.com/mtrudel/bandit/commit/8156921a51e684a951221da7bc30a70a022f722e"}, {"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "url": "https://github.com/mtrudel/bandit/security/advisories/GHSA-frh3-6pv6-rc8j"}, {"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "url": "https://osv.dev/vulnerability/EEF-CVE-2026-39804"}], "sourceIdentifier": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "vulnStatus": "Received", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-770"}], "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "type": "Secondary"}]}

{}