Description
Memory safety bugs present in Firefox 134 and Thunderbird 134. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability was fixed in Firefox 135 and Thunderbird 135.
Published: 2025-02-04
Score: 9.8 Critical
EPSS: < 1% Very Low
KEV: No
Impact: Remote Code Execution
Action: Immediate Patch
AI Analysis

Impact

These memory safety bugs were discovered in Firefox 134 and Thunderbird 134 and involve buffer copy or out‑of‑bounds write vulnerabilities that can corrupt memory. In theory, with sufficient effort an attacker could exploit the corruption to execute arbitrary code on the victim’s system. The weakness is reflected in CWE‑120 and CWE‑787, indicating unsafe handling of memory boundaries.

Affected Systems

Mozilla Firefox 134 and Mozilla Thunderbird 134 are affected. The fixes were released in Firefox 135 and Thunderbird 135 respectively.

Risk and Exploitability

The CVSS score of 9.8 points to a severe risk, but the EPSS score of < 1% suggests that exploitation is unlikely at present. The vulnerability is not listed in the CISA KEV catalog, indicating no confirmed widespread attacks. Nevertheless, the potential for remote code execution makes this a critical upgrade target, especially in environments where vulnerable versions may remain installed.

Generated by OpenCVE AI on April 20, 2026 at 23:52 UTC.

Remediation

No vendor fix or workaround currently provided.

OpenCVE Recommended Actions

  • Apply the latest Mozilla Firefox release (135 or newer) or a patch that brings the client up to the fixed version.
  • Apply the corresponding Thunderbird update to version 135 or later to eliminate the bug.
  • If an immediate update is infeasible, restrict network access to vulnerable clients and monitor for signs of exploitation; evaluate disabling risky extensions or features that might trigger the memory corruption path.

Generated by OpenCVE AI on April 20, 2026 at 23:52 UTC.

Tracking

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Advisories
Source ID Title
EUVD EUVD EUVD-2025-1975 Memory safety bugs present in Firefox 134 and Thunderbird 134. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 135 and Thunderbird < 135.
Ubuntu USN Ubuntu USN USN-7263-1 Firefox vulnerabilities
Ubuntu USN Ubuntu USN USN-7991-1 Thunderbird vulnerabilities
History

Mon, 13 Apr 2026 15:00:00 +0000

Type Values Removed Values Added
Description Memory safety bugs present in Firefox 134 and Thunderbird 134. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 135 and Thunderbird < 135. Memory safety bugs present in Firefox 134 and Thunderbird 134. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability was fixed in Firefox 135 and Thunderbird 135.
Title firefox: thunderbird: Memory safety bugs fixed in Firefox 135 and Thunderbird 135 Memory safety bugs fixed in Firefox 135 and Thunderbird 135

Tue, 15 Jul 2025 13:45:00 +0000

Type Values Removed Values Added
Metrics epss

{'score': 0.00149}

 epss

{'score': 0.00189}

Fri, 07 Feb 2025 14:30:00 +0000

Type Values Removed Values Added
Title firefox: thunderbird: Memory safety bugs fixed in Firefox 135 and Thunderbird 135
Weaknesses CWE-120
References
Metrics threat_severity

None

 threat_severity

Important

Thu, 06 Feb 2025 21:15:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Thu, 06 Feb 2025 20:00:00 +0000

Type Values Removed Values Added
First Time appeared Mozilla
Mozilla firefox
Mozilla thunderbird
Weaknesses CWE-787
CPEs cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:*
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:-:*:*:*
Vendors & Products Mozilla
Mozilla firefox
Mozilla thunderbird
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'}

Tue, 04 Feb 2025 14:15:00 +0000

Type Values Removed Values Added
Description Memory safety bugs present in Firefox 134 and Thunderbird 134. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 135 and Thunderbird < 135.
References

Subscriptions

Mozilla Firefox Thunderbird
cve-icon MITRE

Status: PUBLISHED

Assigner: mozilla

Published:

Updated: 2026-04-13T14:25:25.512Z

Reserved: 2025-02-04T07:26:48.228Z

Link: CVE-2025-1020

cve-icon Vulnrichment

Updated: 2025-02-06T21:06:58.354Z

cve-icon NVD

Status : Modified

Published: 2025-02-04T14:15:32.953

Modified: 2026-04-13T15:16:51.213

Link: CVE-2025-1020

cve-icon Redhat

Severity : Important

Publid Date: 2025-02-04T13:58:56Z

Links: CVE-2025-1020 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-04-21T00:00:13Z

Weaknesses