CVE-2025-5266: Mozilla Firefox · Information Exposure
Affects Mozilla FirefoxSource CVE Database V5
Not known to be exploited · CVSS 4.3 Medium : upgrade to 139 when convenient.
Data as of 26 Oct 2026, 09:08 UTC
- EPSS
- 0.3% chance of exploitation in 30 days – higher than 27% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
- Patch
- Available – fixed in 139
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:NExploitation evidence
Disclosed: evidence found.
CVE published 27 May 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 Mozilla Firefox to 139.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
| Mozilla Firefox | Affected
| Fixed in
|
AI-suggested
An official fix is available and has been released in Firefox 139, Firefox ESR 128.11, Thunderbird 139, and Thunderbird 128.11. Users and administrators should update to these versions or later to remediate this vulnerability. Since the vendor has provided an official fix, applying the update is the recommended mitigation. No additional action is required beyond patching.
Description
Script elements loading cross-origin resources generated load and error events which leaked information enabling XS-Leaks attacks. This vulnerability was fixed in Firefox 139, Firefox ESR 128.11, Thunderbird 139, and Thunderbird 128.11.
References
- bugzilla.mozilla.org/show_bug.cgi?id=1965628 (opens in a new tab)
- mozilla.org/security/advisories/mfsa2025-42/ (opens in a new tab)
- mozilla.org/security/advisories/mfsa2025-44/ (opens in a new tab)
- mozilla.org/security/advisories/mfsa2025-45/ (opens in a new tab)
- mozilla.org/security/advisories/mfsa2025-46/ (opens in a new tab)
- lists.debian.org/debian-lts-announce/2025/05/msg00046.html (opens in a new tab)
- lists.debian.org/debian-lts-announce/2025/05/msg00043.html (opens in a new tab)