CVE-2025-1942Public exploitNetwork attack vector

Memory disclosure via undersized StringChars memcpy

Published Mar 4, 2025 · Updated Jun 4, 2026

Uninitialized-memory disclosure in Mozilla Firefox and Thunderbird before 136 allows remote attackers to read process data via JavaScript. StringChars::maybeRealloc copies InlineLength bytes instead of InlineLength multiplied by sizeof(CharT), leaving part of a widened string backed by uninitialized nursery memory. Exploitation requires JavaScript that expands a string during uppercasing and exposes only a small number of process-memory bytes; scripting is disabled while reading mail in Thunderbird.

CVSS severity9.8
Critical
EPSS probability0.47%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Uninitialized-memory disclosure in Mozilla Firefox and Thunderbird before 136 allows remote attackers to read process data via JavaScript. StringChars::maybeRealloc copies InlineLength bytes instead of InlineLength multiplied by sizeof(CharT), leaving part of a widened string backed by uninitialized nursery memory. Exploitation requires JavaScript that expands a string during uppercasing and exposes only a small number of process-memory bytes; scripting is disabled while reading mail in Thunderbird.

The record

CVE
CVE-2025-1942
Published
Mar 4, 2025
Updated
Jun 4, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-908, T1189
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 4, 2025CVE publishedPublication date reported by the CVE source.
  2. Jun 4, 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 vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

9.8CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-908Use of Uninitialized Resource
T1189Drive-by Compromise

Public exploit references

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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