CVE-2025-1020: Mozjs52 · Memory safety bugs present in Firefox 134 and Thunderbird 134
Affects mozjs52Source GCVE Database
Not known to be exploited · CVSS 9.8 Critical · fixed in 135.0+build2-0ubuntu0.20.04.1 : patch mozjs52 as a priority.
Data as of 28 Oct 2026, 22:28 UTC
- Patch
- Available – fixed in 135.0+build2-0ubuntu0.20.04.1, 1:140.7.1+build1-0ubuntu0.22.04.1
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:HExploitation evidence
Disclosed: evidence found.
CVE published 4 Feb 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.
What to do
Upgrade the Ubuntu to 135.0+build2-0ubuntu0.20.04.1 (firefox package) or 1:140.7.1+build1-0ubuntu0.22.04.1 (thunderbird package).
Patches and advisories
Affected software
| Product | Affected | Fixed in |
|---|---|---|
Ubuntu 24.04 LTSmozjs102pkg:deb/ubuntu/mozjs102?arch=source&distro=nobleOther threats | Affected
| Fixed in– |
Ubuntu 24.04 LTSmozjs115pkg:deb/ubuntu/mozjs115?arch=source&distro=nobleOther threats | Affected
| Fixed in– |
Ubuntu 22.04 LTSmozjs102pkg:deb/ubuntu/mozjs102?arch=source&distro=jammyOther threats | Affected
| Fixed in– |
Ubuntu 22.04 LTSmozjs78pkg:deb/ubuntu/mozjs78?arch=source&distro=jammyOther threats | Affected
| Fixed in– |
Ubuntu 22.04 LTSmozjs91pkg:deb/ubuntu/mozjs91?arch=source&distro=jammyOther threats | Affected
| Fixed in– |
Ubuntu 22.04 LTSthunderbirdpkg:deb/ubuntu/thunderbird?arch=source&distro=jammyOther threats | Affected
| Fixed in
|
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
Description
Memory safety bugs present in Firefox 134 and Thunderbird 134. 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 135 and Thunderbird 135.
References
- ubuntu.com/security/CVE-2025-1020 (opens in a new tab)
- cve.org/CVERecord?id=CVE-2025-1020 (opens in a new tab)
- mozilla.org/en-US/security/advisories/mfsa2025-07/ (opens in a new tab)
- bugzilla.mozilla.org/buglist.cgi?bug_id=1939063%2C1942169 (opens in a new tab)
- mozilla.org/security/advisories/mfsa2025-07/ (opens in a new tab)
- mozilla.org/security/advisories/mfsa2025-11/ (opens in a new tab)
- ubuntu.com/security/notices/USN-7263-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7991-1 (opens in a new tab)