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Fencer Vulns
critical 9.8

CVE-2025-1942 json

Disclosure of uninitialized memory when .toUpperCase() causes string to get longer

published 2025-03-04 20 mo ago modified 2026-10-05 34 d ago also EUVD-2025-7444

cvss
9.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 41%
public exploits
0
none known

Summary

When String.toUpperCase() caused a string to get longer it was possible for uninitialized memory to be incorporated into the result string. This vulnerability was fixed in Firefox 136 and Thunderbird 136.

Patch / fix

  • mozilla firefox 136
  • mozilla thunderbird 136
  • firefox Ubuntu 20.04 LTS 136.0+build3-0ubuntu0.20.04.1
  • thunderbird Ubuntu 22.04 LTS 1:140.7.1+build1-0ubuntu0.22.04.1

ubuntu advisories UBUNTU-CVE-2025-1942

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • firefox-esr openSUSE Tumbleweed 153.0-1.1
  • MozillaFirefox openSUSE Tumbleweed 136.0-1.1

opensuse advisories openSUSE-SU-2026:11373-1openSUSE-SU-2025:14861-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2025-1942 updated cvss 6.3

firefox: Disclosure of uninitialized memory when .toUpperCase() causes string to get longer

  • Red Hat Enterprise Linux 6 firefox
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 7 firefox Red Hat Enterprise Linux 8 firefox Red Hat Enterprise Linux 9 firefox, firefox-x11, firefox-flatpak-container Red Hat Enterprise Linux 10 firefox, firefox-flatpak-container
    affected: no fix available “Fix deferred”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
total
Assessed
19 mo ago

Exploit prediction

0.48% chance of exploitation in the next 30 days, higher than 41% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CISA ADP 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CNA 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

  • Mozilla Firefox
  • Mozilla Thunderbird

Classification

Weakness
  • CWE-908 Use of Uninitialized Resource

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.