CVE-2023-5174: Mozilla Firefox

Critical severity, CVSS 9.8. EPSS: 1.2% chance of exploitation in the next 30 days.

If Windows failed to duplicate a handle during process creation, the sandbox code may have inadvertently freed a pointer twice, resulting in a use-after-free and a potentially exploitable crash. *This bug only affects Firefox on Windows when run in non-standard configurations (such as using `runas`). Other operating systems are unaffected.* This vulnerability affects Firefox < 118, Firefox ESR < 115.3, and Thunderbird < 115.3.

Affected products

• Mozilla Firefox: before 118 (fixed in 118)
• Mozilla Firefox ESR: before 115.3 (fixed in 115.3)
• Mozilla Thunderbird: before 115.3 (fixed in 115.3)

Published 2023-09-27. Last modified 2026-06-17.