CVE-2025-3031: JIT optimization bug with different stack slot sizes

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-04-01 · updated 2026-09-30
Weakness: CWE-200

Description

An attacker could read 32 bits of values spilled onto the stack in a JIT compiled function. This vulnerability was fixed in Firefox 137 and Thunderbird 137.

Affected products

Mozilla Firefox: before 137.0 — fixed in 137.0
Mozilla Thunderbird: before 137.0 — fixed in 137.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 137.0; Mozilla Thunderbird 137.0. Check the vendor advisory for mitigations.

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1947141
https://www.mozilla.org/security/advisories/mfsa2025-20/
https://www.mozilla.org/security/advisories/mfsa2025-23/

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