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CVE-2026-0891 - Firefox Plugin

CVE-2026-0891

Memory safety bugs present in Firefox ESR 140.6, Thunderbird ESR 140.6, Firefox 146 and Thunderbird 146. 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 < 147, Firefox ESR < 140.7, Thunderbird < 147, and Thunderbird < 140.7.

CVE-2026-0891

HIGH CVSS 8.1 Published 2026-01-13 Updated 2026-01-22
AI Risk Elevated (73/100) Active Exploit: No strong signal Published Exploit: No public exploit references Priority: P3 Priority
Severity Band HIGH
CVSS Vector CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Affected Components 3
Reference Links 5
AI Risk Engine Elevated (73/100)
Exploitability High
Active Exploitation No strong signal
Published Exploit Status No public exploit references

Threat Timeline

  1. 2026-01-13 CVE published and first recorded in the threat feed.
  2. 2026-01-22 Record updated with latest vulnerability metadata.
  3. 2026-04-09 AI technical context refreshed for mitigation and impact guidance.
  4. Now Monitoring for follow-up changes, linked references, and new related CVEs.

AI Context

Machine-generated threat intelligence

AI Updated 6 days ago

AI enriched 6 days ago (2026-04-09 07:21 UTC)

Technical Summary

Memory safety bugs present in Firefox ESR 140.6, Thunderbird ESR 140.6, Firefox 146 and Thunderbird 146. 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 < 147, Firefox ESR < 140.7, Thunderbird < 147, and Thunderbird < 140.7.

Potential Impact

Severity is HIGH (CVSS 8.1). Depending on deployment context, affected components may be exposed to unauthorized actions or data integrity risk.

Exploitability Assessment

Exploitability is assessed as High based on severity and technical exposure profile.

Primary risk drivers: severity and technical exposure profile

Mitigation Recommendations

Validate affected product versions, prioritize patching, and monitor references for vendor remediation guidance. If immediate patching is not possible, apply compensating controls and limit exposure of vulnerable surfaces.

Detection & Monitoring

Track authentication anomalies, unexpected file writes, and suspicious plugin API activity around affected components.

Business Impact Lens

Prioritize remediation where affected components process customer data, admin sessions, or Internet-exposed workflows.

Affected Products

Firefox PLUGIN · firefox Affected: >= unspecified, < 147 Fixed in: 147
Firefox ESR PLUGIN · firefox-esr Affected: >= unspecified, < 140.7 Fixed in: 140.7
Thunderbird PLUGIN · thunderbird Affected: >= unspecified, < 147 Fixed in: 140.7
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