Home/CVE/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 Th
CVE

CVE-2026-5731

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 Th

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.

CRITICAL · CVSS 9.8 EPSS 0.00071
Schedule remediation
  • SSVC automatable: yes - attacks can be scripted at scale
  • CVSS base score ≥ 7.0
Sigma rules1 YARA rules0
⬡

Weakness Classification

CWE-119Improper Restriction of Operations within the Bounds of a Memory Buffer
▤

Affected Products & Versions

2
mozilla firefoxall versions
mozilla thunderbirdall versions
◈

Sigma Hunt Rules

1
Exact rules name this CVE ID. Product rules name an affected product in their title. Related rules cover techniques used by actors who exploited this CVE. Showing the most relevant matches; the complete related set is on the full drill-down.
producthighSQLite Firefox Profile Data DB Access
▣

Scoring & Timeline

9.8
CRITICAL · CVSS v3.1 · security@mozilla.org
View on NVD
Attack Vector
Network Adjacent Local Physical
Attack Complexity
Low High
Privileges Required
None Low High
User Interaction
None Required
Scope
Unchanged Changed
Confidentiality
None Low High
Integrity
None Low High
Availability
None Low High
Published to NVD07 Apr 2026 · 01:16 PM
CVSS VectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
SSVC triage · cisa-vulnrichment
Exploitation
none
Automatable
yes
Technical impact
total
SSVC asks the questions that actually drive patch urgency: is it being exploited, can attacks be automated, and how total is the impact.
⚑

Vendor Advisories

30
rhsaRHSA-2026:15889Important
rhsaRHSA-2026:13977Important
rhsaRHSA-2026:13922Important
rhsaRHSA-2026:14303Important
rhsaRHSA-2026:14223Important
🔗

References & Sources

6
Source URLs (vendor pages, mailing lists, write-ups). Exploit/PoC links are in their own section above to avoid duplication.
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%2C2026426Broken Link
https://www.mozilla.org/security/advisories/mfsa2026-25/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-26/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-27/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-28/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-29/Vendor Advisory
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