CVE-2026-6785: Memory safety bugs fixed in Firefox ESR 115.35, Firefox ESR 140.10, Thunderbird ESR 140.10, Firefox 150 and Thunderbird 150

Vulnerability summary

CVE-2026-6785 is a high (CVSS 7.5) Out-of-bounds Read vulnerability in mozilla firefox. EPSS estimates a 0.53% chance of exploitation in the next 30 days, higher than 44.1% of scored vulnerabilities.

Timeline

1. 21-04-2026
   PublishedVulnerability first disclosed.
2. 15-07-2026
   Last modifiedVulnerability information updated.

Description

Memory safety bugs present in Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird ESR 140.9, Firefox 149 and Thunderbird 149. 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 150, Firefox ESR 115.35, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10.

• CWE-125Out-of-bounds ReadThe product reads data past the end, or before the beginning, of the intended buffer.
• CWE-416Use After FreeThe product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.
• CWE-787Out-of-bounds WriteThe product writes data past the end, or before the beginning, of the intended buffer.