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VulnerabilityPublished Updated

CVE-2025-1020: Mozilla Firefox · Out-of-bounds Write

Affects Mozilla FirefoxSource CVE Database V5

0

Not known to be exploited · CVSS 9.8 Critical.

Data as of 26 Oct 2026, 11:07 UTC

CVSS 3.1 base score
9.8Critical
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.5% chance of exploitation in 30 days – higher than 45% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 4 Feb 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 26 Oct 2026.

What to do

Affected software

ProductAffectedFixed in
Mozilla FirefoxAffected
  • =134
Fixed in–

AI-suggested

Mozilla has released official fixes for this vulnerability in Firefox 135 and Thunderbird 135. Users and administrators should upgrade to these or later versions to remediate the issue. The vendor advisories MFSA2025-07 and MFSA2025-11 provide authoritative guidance and confirm that the vulnerability is fixed. Patch status is confirmed as fixed in these versions. No additional mitigation actions are required beyond applying the official updates.

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

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