CVE-2025-1012

Use-after-free during concurrent delazification

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Published Feb 4, 2025 CVSS 3.1 · 9.8 Critical EPSS < 1% KEV · Not listed
Description
A race during concurrent delazification could have led to a use-after-free. This vulnerability was fixed in Firefox 135, Firefox ESR 115.20, Firefox ESR 128.7, Thunderbird 128.7, and Thunderbird 135.

Analysis

AI-generated

Technical impact

A race condition that occurs during concurrent delazification can trigger a use‑after‑free in the rendering engine. This flaw permits the application to access memory that has already been freed, which could lead to memory corruption or unintended data modification. The vulnerability is classified as a memory‑management defect, identified by CWE‑416.

Affected Systems

Mozilla Firefox versions up to 134 (including all Standard and ESR editions below 115.20 and below 128.7) and Mozilla Thunderbird versions below 128.7 and 135. The affected binaries are also distributed in several Red Hat Enterprise Linux environments, notably versions 8 and 9 and their extended service releases (AUS, EUS, TUS, ELS).

Risk and Exploitability

The CVSS score of 9.8 signals a critical severity. The EPSS score is under 1 %, indicating that exploitation activity has been very low so far, and the vulnerability is not listed in the CISA KEV catalog. The description does not detail a usable exploit or a confirmed attack vector, so the risk remains theoretical but the potential impact would be high if exploited.

Remediation

No solution or workaround provided in the CVE record.

OpenCVE Recommended Actions

  • Upgrade to Firefox 135 or later, or to Firefox ESR 115.20/128.7, and to Thunderbird 128.7 or 135 to apply the fix.
  • If an update is not yet available, keep the browsers at the most recent security‑patched release level and limit exposure by avoiding untrusted web content and disabling questionable extensions.
  • Monitor vendor security advisories for any further patches or related concurrency fixes and apply them promptly.

Generated by OpenCVE AI on April 22, 2026 at 04:17 UTC.

Tracking

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Advisories

Source ID Title
Debian DLA Debian DLA DLA-4044-1 firefox-esr security update
Debian DLA Debian DLA DLA-4045-1 thunderbird security update
Debian DSA Debian DSA DSA-5858-1 firefox-esr security update
Debian DSA Debian DSA DSA-5860-1 thunderbird security update
EUVD EUVD EUVD-2025-1967 A race during concurrent delazification could have led to a use-after-free. This vulnerability affects Firefox < 135, Firefox ESR < 115.20, Firefox ESR < 128.7, Thunderbird < 128.7, and Thunderbird < 135.
Ubuntu USN Ubuntu USN USN-7263-1 Firefox vulnerabilities
Ubuntu USN Ubuntu USN USN-7663-1 Thunderbird vulnerabilities
History
Type Values Removed Values Added
Description A race during concurrent delazification could have led to a use-after-free. This vulnerability affects Firefox < 135, Firefox ESR < 115.20, Firefox ESR < 128.7, Thunderbird < 128.7, and Thunderbird < 135. A race during concurrent delazification could have led to a use-after-free. This vulnerability was fixed in Firefox 135, Firefox ESR 115.20, Firefox ESR 128.7, Thunderbird 128.7, and Thunderbird 135.
Title firefox: thunderbird: Use-after-free during concurrent delazification Use-after-free during concurrent delazification
Type Values Removed Values Added
Metrics epss

{'score': 0.00124}

 epss

{'score': 0.00176}
Type Values Removed Values Added
CPEs cpe:/a:redhat:enterprise_linux:8
Type Values Removed Values Added
Title firefox: thunderbird: Use-after-free during concurrent delazification
First Time appeared Redhat
Redhat enterprise Linux
Redhat rhel Aus
Redhat rhel E4s
Redhat rhel Els
Redhat rhel Eus
Redhat rhel Tus
CPEs cpe:/a:redhat:enterprise_linux:9
cpe:/a:redhat:rhel_aus:8.2
cpe:/a:redhat:rhel_aus:8.4
cpe:/a:redhat:rhel_aus:8.6
cpe:/a:redhat:rhel_e4s:8.4
cpe:/a:redhat:rhel_e4s:8.6
cpe:/a:redhat:rhel_e4s:9.0
cpe:/a:redhat:rhel_eus:8.8
cpe:/a:redhat:rhel_eus:9.2
cpe:/a:redhat:rhel_eus:9.4
cpe:/a:redhat:rhel_tus:8.4
cpe:/a:redhat:rhel_tus:8.6
cpe:/o:redhat:rhel_els:7
Vendors & Products Redhat
Redhat enterprise Linux
Redhat rhel Aus
Redhat rhel E4s
Redhat rhel Els
Redhat rhel Eus
Redhat rhel Tus
References
Metrics threat_severity

None

 threat_severity

Moderate
Type Values Removed Values Added
First Time appeared Mozilla
Mozilla firefox
Mozilla thunderbird
CPEs cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:*
cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:*
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:-:*:*:*
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:esr:*:*:*
Vendors & Products Mozilla
Mozilla firefox
Mozilla thunderbird
Type Values Removed Values Added
Weaknesses CWE-416
Metrics cvssV3_1

{'score': 9.8, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'}

ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}
Type Values Removed Values Added
Description A race during concurrent delazification could have led to a use-after-free. This vulnerability affects Firefox < 135, Firefox ESR < 115.20, Firefox ESR < 128.7, Thunderbird < 128.7, and Thunderbird < 135.
References
Earlier changes (3)
Weaknesses

Sources

Status
PUBLISHED
Assigner
mozilla
Published
Updated
Apr 13, 2026, 2:25 PM
Reserved
Feb 4, 2025, 7:26 AM

View source JSON

Updated
Nov 3, 2025, 8:56 PM

JSON

Status
Modified
Published
Feb 4, 2025, 2:15 PM
Modified
Oct 5, 2026, 3:10 PM

View source JSON

Severity
Moderate
Public date
Feb 4, 2025, 1:58 PM

View source Bugzilla JSON

Updated
Apr 22, 2026, 4:30 AM

JSON