Memory safety bugs fixed in Firefox ESR 115.34.1, Firefox ESR 140.9.1, Thunderbird ESR 140.9.1, Firefox 149.0.2 and Thunderbird 149.0.2

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Summary

CVECVE-2026-5731
StatePUBLISHED
Assignermozilla
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-04-07 13:16:47 UTC
Updated2026-04-07 19:16:47 UTC
DescriptionMemory safety bugs present in Firefox ESR 115.34.0, 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 < 115.34.1, Firefox ESR < 140.9.1, Thunderbird < 149.0.2, and Thunderbird < 140.9.1.

Risk And Classification

Primary CVSS: v3.1 9.8 CRITICAL from ADP

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Problem Types: CWE-119 | CWE-119 CWE-119 Improper Restriction of Operations within the Bounds of a Memory Buffer

VersionSourceTypeScoreSeverityVector
3.1ADPDECLARED9.8CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
3.1134c704f-9b21-4f2e-91b3-4a467353bcc0Secondary9.8CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Mozilla Firefox affected unspecified 149.0.2 custom Not specified
CNA Mozilla Firefox ESR affected unspecified 115.34.1 custom Not specified
CNA Mozilla Firefox ESR affected unspecified 140.9.1 custom Not specified
CNA Mozilla Thunderbird affected unspecified 149.0.2 custom Not specified
CNA Mozilla Thunderbird affected unspecified 140.9.1 custom Not specified

References

ReferenceSourceLinkTags
bugzilla.mozilla.org/buglist.cgi [email protected] bugzilla.mozilla.org
www.mozilla.org/security/advisories/mfsa2026-29 [email protected] www.mozilla.org
www.mozilla.org/security/advisories/mfsa2026-28 [email protected] www.mozilla.org
www.mozilla.org/security/advisories/mfsa2026-26 [email protected] www.mozilla.org
www.mozilla.org/security/advisories/mfsa2026-27 [email protected] www.mozilla.org
www.mozilla.org/security/advisories/mfsa2026-25 [email protected] www.mozilla.org
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: Brian Grinstead, Christian Holler, Tom Schuster and the Mozilla Fuzzing Team (en)

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