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VulnerabilityPublished Updated

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

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Authoritative record:CVE-2025-1933· High 7.6

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

CVSS 3.1 base score
7.6High
How severe the flaw is on the 0–10 CVSS scale.
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:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 4 Mar 2025

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq 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

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