CVE-2026-5731CRITICAL 9.8EPSS p25.4%

CVE-2026-5731CVE-2026-5731

Description

Memory safety bugs present in Firefox ESR 115.34.0, Firefox ESR 140.9.0, Thunderbird ESR 140.9.0, Firefox 149.0.1 and Thunderbird 149.0.1. 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 149.0.2, Firefox ESR 115.34.1, Firefox ESR 140.9.1, Thunderbird 149.0.2, and Thunderbird 140.9.1.

Scoring

CVSS 3.19.8 (CRITICAL)
VectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS0.34% probability of exploitation · percentile 25.4% · 2026-06-19T12:03:05Z
Published2026-04-07
Last modified2026-04-16

Underlying weaknesses· 1

CWE-119

References

  1. https://bugzilla.mozilla.org/buglist.cgi?bug_id=2021894%2C2022225%2C2022252%2C2022294%2C2023007%2C2023130%2C2023191%2C2023364%2C2023829%2C2024074%2C2024417%2C2024433%2C2024436%2C2024437%2C2024453%2C2024461%2C2024462%2C2024472%2C2024474%2C2024477%2C2025364%2C2025401%2C2025402%2C2025472%2C2026287%2C2026299%2C2026305%2C2026426
  2. https://www.mozilla.org/security/advisories/mfsa2026-25/
  3. https://www.mozilla.org/security/advisories/mfsa2026-26/
  4. https://www.mozilla.org/security/advisories/mfsa2026-27/
  5. https://www.mozilla.org/security/advisories/mfsa2026-28/
  6. https://www.mozilla.org/security/advisories/mfsa2026-29/

1

TypeTargetConfidenceTier
WeaknessImproper Restriction of Operations within the Bounds of a Memory Buffercwe-1190%live

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Sourced from NVD + FIRST.org EPSS. Curated for EU compliance use cases by Adam Lundqvist, Founder at SQUR.