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CVE-2025-1933: JIT corruption of WASM i32 return values on 64-bit CPUs

• Severity: high (CVSS 7.6 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: 2025-03-04 · updated 2026-10-05

Description

On 64-bit CPUs, when the JIT compiles WASM i32 return values they can pick up bits from left over memory. This can potentially cause them to be treated as a different type. This vulnerability was fixed in Firefox 136, Firefox ESR 115.21, Firefox ESR 128.8, Thunderbird 136, and Thunderbird 128.8.

Affected products

• Mozilla Firefox: before 115.21.0; before 136.0; from 116.0 before 128.8.0 — fixed in 115.21.0, 128.8.0, 136.0
• Mozilla Thunderbird: before 128.8; from 129.0 before 136.0 — fixed in 128.8, 136.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 115.21.0, 128.8.0, 136.0; Mozilla Thunderbird 128.8, 136.0. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=1946004
• https://www.mozilla.org/security/advisories/mfsa2025-14/
• https://www.mozilla.org/security/advisories/mfsa2025-15/
• https://www.mozilla.org/security/advisories/mfsa2025-16/
• https://www.mozilla.org/security/advisories/mfsa2025-17/
• https://www.mozilla.org/security/advisories/mfsa2025-18/
• https://lists.debian.org/debian-lts-announce/2025/03/msg00006.html

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