CVE-2025-1933: On 64-bit CPUs, when the JIT compiles WASM i32 return values they can pick up bits from left over memory
Source GCVE Database
Not known to be exploited · CVSS 7.6 High · fixed in 136 : patch affected systems soon.
Data as of 30 Oct 2026, 01:15 UTC
- Patch
- Available – fixed in 136, 128.8, 115.21
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:HExploitation evidence
Disclosed: evidence found.
CVE published 4 Mar 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.
What to do
AI-suggested
This vulnerability is fixed in Firefox 136, Firefox ESR 115.21, and Firefox ESR 128.8. Users and administrators should update to these versions or later to remediate the issue. No additional mitigation steps are required as the vendor advisory confirms an official fix is available.
Description
CVE-2025-1933 is a high severity vulnerability in Firefox's Just-In-Time (JIT) compiler for WebAssembly (WASM) on 64-bit CPUs. The JIT compiler can incorrectly handle i32 return values by including bits from leftover memory, potentially causing these values to be treated as a different type. This flaw affects Firefox versions prior to 136 and Firefox ESR versions prior to 115.21 and 128.8. The issue was fixed in Firefox 136 and the corresponding ESR releases.
References
- nvd.nist.gov/vuln/detail/CVE-2025-1933 (opens in a new tab)
- bugzilla.mozilla.org/show_bug.cgi?id=1946004 (opens in a new tab)
- lists.debian.org/debian-lts-announce/2025/03/msg00006.html (opens in a new tab)
- mozilla.org/security/advisories/mfsa2025-14 (opens in a new tab)
- mozilla.org/security/advisories/mfsa2025-15 (opens in a new tab)
- mozilla.org/security/advisories/mfsa2025-16 (opens in a new tab)
- mozilla.org/security/advisories/mfsa2025-17 (opens in a new tab)
- mozilla.org/security/advisories/mfsa2025-18 (opens in a new tab)