Memory safety bugs present in Firefox ESR 140.9.0, Thunderbird ESR 140.9.0, Firefox 149.0.1 and Thunderbird 149.0.1. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability was fixed in Firefox 149.0.2, Firefox ESR 140.9.1, Thunderbird 149.0.2, and Thunderbird 140.9.1.
References
Link Providers
https://access.redhat.com/errata/RHSA-2026:11805 cve-icon
https://access.redhat.com/errata/RHSA-2026:11813 cve-icon
https://access.redhat.com/errata/RHSA-2026:12264 cve-icon
https://access.redhat.com/errata/RHSA-2026:13342 cve-icon
https://access.redhat.com/errata/RHSA-2026:13412 cve-icon
https://access.redhat.com/errata/RHSA-2026:13533 cve-icon
https://access.redhat.com/errata/RHSA-2026:13582 cve-icon
https://access.redhat.com/errata/RHSA-2026:13583 cve-icon
https://access.redhat.com/errata/RHSA-2026:13596 cve-icon
https://access.redhat.com/errata/RHSA-2026:13600 cve-icon
https://access.redhat.com/errata/RHSA-2026:13665 cve-icon
https://access.redhat.com/errata/RHSA-2026:13682 cve-icon
https://access.redhat.com/errata/RHSA-2026:13683 cve-icon
https://access.redhat.com/errata/RHSA-2026:13922 cve-icon
https://access.redhat.com/errata/RHSA-2026:13977 cve-icon
https://access.redhat.com/errata/RHSA-2026:14223 cve-icon
https://access.redhat.com/errata/RHSA-2026:14303 cve-icon
https://access.redhat.com/errata/RHSA-2026:15889 cve-icon
https://access.redhat.com/errata/RHSA-2026:7671 cve-icon
https://access.redhat.com/errata/RHSA-2026:7672 cve-icon
https://access.redhat.com/errata/RHSA-2026:8052 cve-icon
https://access.redhat.com/errata/RHSA-2026:8459 cve-icon
https://access.redhat.com/errata/RHSA-2026:9345 cve-icon
https://access.redhat.com/errata/RHSA-2026:9638 cve-icon
https://access.redhat.com/security/cve/CVE-2026-5734 cve-icon
https://bugzilla.mozilla.org/buglist.cgi?bug_id=2022369%2C2023026%2C2023545%2C2023555%2C2023958%2C2025422%2C2025468%2C2025492%2C2025505 cve-icon cve-icon
https://bugzilla.redhat.com/show_bug.cgi?id=2455897 cve-icon
https://nvd.nist.gov/vuln/detail/CVE-2026-5734 cve-icon
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-5734.json cve-icon
https://www.cve.org/CVERecord?id=CVE-2026-5734 cve-icon
https://www.mozilla.org/security/advisories/mfsa2026-25/ cve-icon cve-icon
https://www.mozilla.org/security/advisories/mfsa2026-27/ cve-icon cve-icon
https://www.mozilla.org/security/advisories/mfsa2026-27/#CVE-2026-5734 cve-icon
https://www.mozilla.org/security/advisories/mfsa2026-28/ cve-icon cve-icon
https://www.mozilla.org/security/advisories/mfsa2026-29/ cve-icon cve-icon
https://www.mozilla.org/security/advisories/mfsa2026-29/#CVE-2026-5734 cve-icon
History

Mon, 13 Apr 2026 14:30:00 +0000

Type Values Removed Values Added
Description Memory safety bugs present in Firefox ESR 140.9.0, Thunderbird ESR 140.9.0, Firefox 149.0.1 and Thunderbird 149.0.1. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 149.0.2, Firefox ESR < 140.9.1, Thunderbird < 149.0.2, and Thunderbird < 140.9.1. Memory safety bugs present in Firefox ESR 140.9.0, Thunderbird ESR 140.9.0, Firefox 149.0.1 and Thunderbird 149.0.1. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability was fixed in Firefox 149.0.2, Firefox ESR 140.9.1, Thunderbird 149.0.2, and Thunderbird 140.9.1.

Mon, 13 Apr 2026 14:15:00 +0000

Type Values Removed Values Added
Weaknesses CWE-120
Metrics cvssV3_1

{'score': 9.8, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'}

ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}

cvssV3_1

{'score': 8.1, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H'}


Wed, 08 Apr 2026 20:15:00 +0000

Type Values Removed Values Added
First Time appeared Mozilla firefox Esr
Vendors & Products Mozilla firefox Esr

Wed, 08 Apr 2026 12:30:00 +0000


Tue, 07 Apr 2026 20:45:00 +0000

Type Values Removed Values Added
Description Memory safety bugs present in Firefox ESR 140.9.0, Thunderbird ESR 140.9.0, Firefox 149.0.1 and Thunderbird 149.0.1. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 149.0.2 and Firefox ESR < 140.9.1. Memory safety bugs present in Firefox ESR 140.9.0, Thunderbird ESR 140.9.0, Firefox 149.0.1 and Thunderbird 149.0.1. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 149.0.2, Firefox ESR < 140.9.1, Thunderbird < 149.0.2, and Thunderbird < 140.9.1.
First Time appeared Mozilla
Mozilla firefox
Mozilla thunderbird
Weaknesses CWE-787
CPEs cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:*
cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:*
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:-:*:*:*
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:esr:*:*:*
Vendors & Products Mozilla
Mozilla firefox
Mozilla thunderbird
References
Metrics cvssV3_1

{'score': 9.8, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'}


Tue, 07 Apr 2026 15:15:00 +0000

Type Values Removed Values Added
Description Memory safety bugs present in Firefox ESR 140.9.0, Thunderbird ESR 140.9.0, Firefox 149.0.1 and Thunderbird 149.0.1. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 149.0.2 and Firefox ESR < 140.9.1.
Title Memory safety bugs fixed in Firefox ESR 140.9.1, Thunderbird ESR 140.9.1, Firefox 149.0.2 and Thunderbird 149.0.2
References

cve-icon MITRE

Status: PUBLISHED

Assigner: mozilla

Published: 2026-04-07T12:43:14.833Z

Updated: 2026-07-15T00:42:12.685Z

Reserved: 2026-04-07T12:43:14.328Z

Link: CVE-2026-5734

cve-icon Vulnrichment

Updated: 2026-07-15T00:42:12.685Z

cve-icon NVD

Status : Modified

Published: 2026-04-07T13:16:47.667

Modified: 2026-07-15T01:16:44.727

Link: CVE-2026-5734

cve-icon Redhat

Severity : Important

Publid Date: 2026-04-07T12:43:14Z

Links: CVE-2026-5734 - Bugzilla