Internally found bugs fixed in Thunderbird ESR 140.14, Thunderbird ESR 153.1 and Thunderbird 154

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-74987
StatePUBLISHED
Assignermozilla
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-18 13:17:40 UTC
Updated2026-08-19 15:19:36 UTC
DescriptionInternally found bugs present in Thunderbird ESR 140.13, Thunderbird ESR 153.0 and Thunderbird 153. Some of these bugs showed evidence of memory corruption or another security-relevant defect and we presume that with enough effort some of these could have been exploited. This vulnerability was fixed in Firefox 154, Firefox ESR 140.14, Firefox ESR 153.1, Thunderbird 154, Thunderbird 140.14, and Thunderbird 153.1.

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

EPSS: 0.001840000 probability, percentile 0.083560000 (date 2026-08-19)

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

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Mozilla Firefox All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Mozilla Firefox unaffected 140.14 140.* rpm Not specified
CNA Mozilla Firefox unaffected 153.1 153.* rpm Not specified
CNA Mozilla Firefox unaffected 154 * rpm Not specified
CNA Mozilla Thunderbird unaffected 140.14 140.* rpm Not specified
CNA Mozilla Thunderbird unaffected 153.1 153.* rpm Not specified
CNA Mozilla Thunderbird unaffected 154 * rpm Not specified

References

ReferenceSourceLinkTags
bugzilla.mozilla.org/show_bug.cgi [email protected] bugzilla.mozilla.org Permissions Required
bugzilla.mozilla.org/buglist.cgi [email protected] bugzilla.mozilla.org Broken Link
bugzilla.mozilla.org/buglist.cgi [email protected] bugzilla.mozilla.org Broken Link
www.mozilla.org/security/advisories/mfsa2026-78 [email protected] www.mozilla.org Vendor Advisory
www.mozilla.org/security/advisories/mfsa2026-79 [email protected] www.mozilla.org Vendor Advisory
www.mozilla.org/security/advisories/mfsa2026-77 [email protected] www.mozilla.org Vendor Advisory
www.mozilla.org/security/advisories/mfsa2026-76 [email protected] www.mozilla.org Vendor Advisory
www.mozilla.org/security/advisories/mfsa2026-74 [email protected] www.mozilla.org Vendor Advisory
www.mozilla.org/security/advisories/mfsa2026-80 [email protected] www.mozilla.org Vendor Advisory
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: Nicolas Silva, Tom Ritter and the Mozilla Fuzzing Team (en)

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