CVE-2025-0240

Client crash via cross-compartment JSON module result

Published Jan 7, 2025 · Updated Apr 13, 2026

Use-after-free in Mozilla's JavaScript engine in Firefox and Thunderbird before 134 allows local users to crash affected clients. SyntheticModuleEvaluate forwards an unset evaluation result instead of undefined to promise resolution across a different compartment, creating invalid cross-compartment access. Triggering requires JSON-module evaluation across distinct compartments; ordinary Thunderbird email reading disables scripting and does not expose this route.

CVSS severity4.0
Medium
EPSS probability0.67%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Use-after-free in Mozilla's JavaScript engine in Firefox and Thunderbird before 134 allows local users to crash affected clients. SyntheticModuleEvaluate forwards an unset evaluation result instead of undefined to promise resolution across a different compartment, creating invalid cross-compartment access. Triggering requires JSON-module evaluation across distinct compartments; ordinary Thunderbird email reading disables scripting and does not expose this route.

The record

CVE
CVE-2025-0240
Published
Jan 7, 2025
Updated
Apr 13, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-416, T1203
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 7, 2025CVE publishedPublication date reported by the CVE source.
  2. Apr 13, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

4.0CISA-ADPCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-416Use After Free
T1203Exploitation for Client Execution

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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