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7.5

Firefox and Thunderbird could let attackers run code

CVE-2026-0891 · published 9 months ago
Summary

Certain older versions of Firefox (including ESR 140.6) and Thunderbird (including ESR 140.6) contain memory handling errors that could let a skilled attacker execute their own programs on a user's computer. The problem has been corrected in Firefox 147, Firefox ESR 140.7, Thunderbird 147, and Thunderbird 140.7. Upgrade the browsers and email client to these newer versions as soon as possible.

What to do
  • Update debian firefox-esr to version 140.7.0esr-1~deb11u1.
  • Update debian firefox-esr to version 140.7.0esr-1~deb12u1.
  • Update debian firefox-esr to version 140.7.0esr-1~deb13u1.
  • Update debian firefox-esr to version 140.7.0esr-1.
  • Update debian thunderbird to version 1:140.7.0esr-1~deb11u1.
  • Update debian thunderbird to version 1:140.7.0esr-1~deb12u1.
  • Update canonical thunderbird to version 1:140.7.1+build1-0ubuntu0.22.04.1.
  • Update debian thunderbird to version 1:140.7.0esr-1~deb13u1.
  • Update debian thunderbird to version 1:140.7.0esr-1.
Affected software
Ecosystem VendorProductAffected versions
– mozilla firefox < 140.7.0
< 147.0
cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:*
– mozilla thunderbird < 140.7.0
< 147.0
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:esr:*:*:*
Debian:11 debian firefox-esr < 140.7.0esr-1~deb11u1
Fix: upgrade to 140.7.0esr-1~deb11u1
Debian:12 debian firefox-esr < 140.7.0esr-1~deb12u1
Fix: upgrade to 140.7.0esr-1~deb12u1
Debian:13 debian firefox-esr < 140.7.0esr-1~deb13u1
Fix: upgrade to 140.7.0esr-1~deb13u1
Debian:14 debian firefox-esr < 140.7.0esr-1
Fix: upgrade to 140.7.0esr-1
Debian:11 debian thunderbird < 1:140.7.0esr-1~deb11u1
Fix: upgrade to 1:140.7.0esr-1~deb11u1
Debian:12 debian thunderbird < 1:140.7.0esr-1~deb12u1
Fix: upgrade to 1:140.7.0esr-1~deb12u1
Ubuntu:18.04:LTS canonical mozjs52 All versions
Ubuntu:18.04:LTS canonical mozjs38 All versions
Ubuntu:20.04:LTS canonical mozjs68 All versions
Ubuntu:22.04:LTS canonical mozjs102 All versions
Ubuntu:22.04:LTS canonical mozjs78 All versions
Ubuntu:22.04:LTS canonical mozjs91 All versions
Ubuntu:22.04:LTS canonical thunderbird < 1:140.7.1+build1-0ubuntu0.22.04.1
Fix: upgrade to 1:140.7.1+build1-0ubuntu0.22.04.1
Ubuntu:24.04:LTS canonical mozjs115 All versions
Debian:13 debian thunderbird < 1:140.7.0esr-1~deb13u1
Fix: upgrade to 1:140.7.0esr-1~deb13u1
Debian:14 debian thunderbird < 1:140.7.0esr-1
Fix: upgrade to 1:140.7.0esr-1
Original advisory text
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 effo...
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 was fixed in Firefox 147, Firefox ESR 140.7, Thunderbird 147, and Thunderbird 140.7.
References
Fix within
Internet-facing 14 days
Internal At next upgrade
  • Not known to be exploited
  • Needs hands-on effort to exploit
  • Gives an attacker full control
Severity
7.5 High
Exploitation
<1% chance of attack within 30 days
Type
CWE-119Buffer Overflow
Timeline
Published13 Jan 2026
Updated4 Nov 2026
First seen7 Mar 2026
Sources
CVE-2026-0891 · OSV
DEBIAN-CVE-2026-0891 · OSV
CVE-2026-0891 · NVD
CVE-2026-0891 · MITRE
UBUNTU-CVE-2026-0891 · OSV
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