Memory Safety Vulnerabilities in Firefox and Thunderbird by Mozilla
CVE-2026-0891

8.1HIGH

Key Information:

Vendor

Mozilla
Status
Firefox
Firefox Esr
Thunderbird
Vendor
CVE Published:
13 January 2026

What is CVE-2026-0891?

Multiple memory safety bugs exist in Firefox and Thunderbird, which go unnoticed in versions prior to Firefox 147 and Thunderbird 147. These flaws have shown signs of memory corruption, indicating that, with significant effort, these vulnerabilities could potentially be exploited to execute arbitrary code. The affected versions are Firefox ESR 140.6 and Thunderbird ESR 140.6, among others. Affected users are encouraged to update to the latest versions to safeguard against potential exploits.

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Affected Version(s)

Firefox < 147

Firefox ESR < 140.7

Thunderbird < 147

References

https://bugzilla.mozilla.org/buglist.cgi?bug_id=1964722%2...
https://www.mozilla.org/security/advisories/mfsa2026-01/
https://www.mozilla.org/security/advisories/mfsa2026-03/

CVSS V3.1

Score:
8.1
Severity:
HIGH
Confidentiality:
High
Integrity:
High
Availability:
High
Attack Vector:
Network
Attack Complexity:
High
Privileges Required:
None
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Andrew McCreight, Dennis Jackson and the Mozilla Fuzzing Team
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