CVE-2025-6436: mozilla firefox

Vulnerability summary

CVE-2025-6436 is a high (CVSS 8.1) vulnerability in mozilla firefox. EPSS estimates a 4.26% chance of exploitation in the next 30 days, higher than 90.9% of scored vulnerabilities.

Timeline

1. 24-06-2025
   PublishedVulnerability first disclosed.
2. 13-04-2026
   Last modifiedVulnerability information updated.

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.

• CWE-119Improper Restriction of Operations within the Bounds of a Memory BufferThe product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.