CVE-2026-5731

CRITICAL

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

Title source: cna
STIX 2.1

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.

References (33)

Core 33
Core References

Scores

CVSS v3 9.8
EPSS 0.0034
EPSS Percentile 26.6%
Attack Vector NETWORK
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CISA SSVC

Vulnrichment
Exploitation none
Automatable no
Technical Impact total

Details

CWE
CWE-119 CWE-787
Status published
Products (15)
mozilla/firefox 115.34.0
mozilla/firefox 140.9.0
mozilla/firefox 149.0.1
Mozilla/Firefox 115.34.1 - 115.*
Mozilla/Firefox 140.9.1 - 140.*
Mozilla/Firefox 149.0.2
Mozilla/Firefox unspecified - 149.0.2
Mozilla/Firefox ESR unspecified - 115.34.1
Mozilla/Firefox ESR unspecified - 140.9.1
mozilla/thunderbird 140.9.0
... and 5 more
Published Apr 07, 2026
Tracked Since Apr 07, 2026