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CVE-2026-5731VulnerabilityPublished Updated

Red Hat Security Advisory: firefox security update

Affects Red Hat firefoxSource GCVE Database

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Mentioned vulnerabilities

Authoritative record:CVE-2026-5731· Critical 9.8

Not known to be exploited · CVSS 9.8 Critical : upgrade the Red Hat redhat/firefox package to 140.9.1 as a priority.

Data as of 29 Oct 2026, 19:04 UTC

CVSS 3.1 base score
9.8Critical
How severe the flaw is on the 0–10 CVSS scale.
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 140.9.1
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 7 Apr 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: 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 29 Oct 2026.

What to do

Upgrade the Red Hat redhat/firefox package to 140.9.1.

Affected software

ProductAffectedFixed in
Red Hatredhat/firefoxpkg:rpm/redhat/firefoxOther threatsAffected
  • <140.9.1
Fixed in
  • 140.9.1

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

A security update is available from Red Hat for Firefox and Thunderbird packages in Red Hat Enterprise Linux 8.2. Users should apply the update to Firefox ESR 140.9.1 or later and Thunderbird ESR 140.9.1 or later to remediate these vulnerabilities. Refer to the Red Hat advisory RHSA-2026:11805 and the article https://access.redhat.com/articles/11258 for detailed update instructions. No additional mitigations are indicated by the vendor.

Description

Mozilla Firefox is an open-source web browser, designed for standards compliance, performance, and portability. Security Fix(es): * libpng: libpng: Arbitrary code execution due to use-after-free vulnerability (CVE-2026-33416) * libpng: libpng: Information disclosure and denial of service via out-of-bounds read/write in Neon palette expansion (CVE-2026-33636) * thunderbird: firefox: Memory safety bugs fixed in Firefox ESR 140.9.1, Thunderbird ESR 140.9.1, Firefox 149.0.2 and Thunderbird 149.0.2 (CVE-2026-5734) * thunderbird: firefox: Memory safety bugs fixed in Firefox ESR 115.34.1, Firefox ESR 140.9.1, Thunderbird ESR 140.9.1, Firefox 149.0.2 and Thunderbird 149.0.2 (CVE-2026-5731) * firefox: thunderbird: Incorrect boundary conditions, integer overflow in the Graphics: Text component (CVE-2026-5732) For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

References

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