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CVE-2025-5263VulnerabilityPublished Updated

CVE-2025-5263: Mozilla Firefox · Vulnerability

Affects Mozilla FirefoxSource CVE Database V5

0

Not known to be exploited · CVSS 4.3 Medium : upgrade to 139 when convenient.

Data as of 25 Oct 2026, 19:02 UTC

CVSS 3.1 base score
4.3Medium
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.2% chance of exploitation in 30 days – higher than 18% 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:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 27 May 2025

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq 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 2026-10-25.

What to do

Upgrade Mozilla Firefox to 139.

Affected software

ProductAffectedFixed in
Mozilla FirefoxAffected
  • <139
Fixed in
  • 139

AI-suggested

Official fixes for this vulnerability are available and have been released in Firefox 139, Firefox ESR 115.24, Firefox ESR 128.11, Thunderbird 139, and Thunderbird 128.11. Users and administrators should update to these versions or later to remediate the issue. No additional mitigation steps are required beyond applying these updates as per the Mozilla security advisories.

Description

Error handling for script execution was incorrectly isolated from web content, which could have allowed cross-origin leak attacks. This vulnerability was fixed in Firefox 139, Firefox ESR 115.24, Firefox ESR 128.11, Thunderbird 139, and Thunderbird 128.11.

References

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