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No exploitation reportedFix available

CVE-2025-6436

Memory safety bugs fixed in Firefox 140 and Thunderbird 140

No exploitation reported by the sources we read.

  • Published2025-06-24
  • Fixed in140.0
  • WeaknessCWE-119

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

Memory safety bugs present in Firefox 139 and Thunderbird 139. 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 140 and Thunderbird 140.

Timeline

dates in UTC
  1. 2025-06-2413:15CVE publishedNVD

Versions per branch

NVD
Mozilla firefox
BranchAffectedFixed in
140.0< 140.0140.0
Mozilla thunderbird
BranchAffectedFixed in
140.0< 140.0140.0

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Products declared by the CNA2 products

As mozilla, the CNA that assigned this CVE, declared them in the CVE record; versions as written.

  • Mozilla Firefox

    Not affected ≥ 140

  • Mozilla Thunderbird

    Not affected ≥ 140

Source: the CNA record (CVE Program), © The MITRE Corporation,CVE Terms of UseCVE recordupdated 2026-04-13

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • firefoxWolfiall versions · fixed in 140-r0
  • firefoxChainguardall versions · fixed in 140-r0and 1 other package
  • firefox-esropenSUSE:Tumbleweedall versions · fixed in 140.1.0-1.1and 1 other package
  • MozillaFirefoxSUSE:Linux Enterprise Server LTSS Extended Security 12 SP5all versions · fixed in 140.0-112.270.2
  • MozillaFirefoxSUSE:Linux Enterprise Server for SAP Applications 15 SP5all versions · fixed in 140.1.0-150200.152.193.1
  • MozillaFirefoxSUSE:Linux Enterprise Server for SAP Applications 15 SP4all versions · fixed in 140.1.0-150200.152.193.1
  • MozillaFirefoxSUSE:Linux Enterprise Server for SAP Applications 15 SP3all versions · fixed in 140.1.0-150200.152.193.1
  • MozillaFirefoxSUSE:Linux Enterprise Server 15 SP5-LTSSall versions · fixed in 140.1.0-150200.152.193.1

66 more package ranges on OSV.dev

Vendor advisories

  • CVE-2025-6436 Red Hat Product Security

    firefox: Memory safety bugs fixed in Firefox 140 and Thunderbird 140

Full record on NVD

Fix

  1. Update Mozilla firefox to 140.0

Advisories and patches

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof of concept
Metasploit modules
none listed
Metasploit Framework

Sources

Identifiers

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Published
2025-06-24
Last Modified
2026-09-30
NVD status
Modified
GitHub Advisory
GHSA-x8w4-qgw5-r433

Frequently asked questions

What is CVE-2025-6436?

Memory safety bugs present in Firefox 139 and Thunderbird 139. 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 140 and Thunderbird 140.

Is CVE-2025-6436 actively exploited?

Active exploitation of CVE-2025-6436 has not been confirmed. Its EPSS score was 4.3% on 2026-11-08, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2025-6436?

CVE-2025-6436 has a CVSS v3 base score of 8.1 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H.

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