Description
Use-after-free in the Layout: Text and Fonts component. This vulnerability was fixed in Firefox ESR 153.4, Thunderbird 157, Thunderbird 140.17, Thunderbird 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17.
Published: 2026-09-29
Score: 8.8 High
EPSS: < 1% Very Low
KEV: No
Impact: Remote code execution
Action: Immediate Patch
AI Analysis

Impact

This vulnerability is a use‑after‑free flaw in the Layout: Text and Fonts component of Mozilla Firefox and Thunderbird. The flaw occurs when the browser accesses memory that has already been freed, which can lead to memory corruption. Based on the nature of use‑after‑free conditions, it is inferred that an attacker could potentially crash the application or execute arbitrary code if the flaw is exploited.

Affected Systems

Mozilla Firefox and Mozilla Thunderbird are affected. The vulnerability was fixed in Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17, as well as Thunderbird 157, Thunderbird 140.17, and Thunderbird 153.4. Users running older ESR or legacy builds of either product should be aware that they remain vulnerable.

Risk and Exploitability

The EPSS score of less than 1% and the absence of the vulnerability from CISA’s KEV catalog suggest a low likelihood of exploitation, but the CVSS score of 8.8 indicates high severity. Use‑after‑free flaws can lead to arbitrary code execution or browser crashes, presenting a serious risk for unpatched systems.

Generated by OpenCVE AI on October 7, 2026 at 07:15 UTC.

Remediation

No solution or workaround provided in the CVE record.

OpenCVE Recommended Actions

  • Upgrade to Firefox ESR 153.4 or newer, Firefox 157 or newer, or the latest ESR 115.42/140.17 build that includes the patch.
  • Restart all instances of the browser to clear any residual memory state.
  • Monitor browser logs for crashes or suspicious memory accesses as a temporary indicator that the vulnerability has not been fully mitigated.

Generated by OpenCVE AI on October 7, 2026 at 07:15 UTC.

Tracking

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Advisories
Source ID Title
Debian DLA Debian DLA DLA-4810-1 thunderbird security update
Debian DLA Debian DLA DLA-4814-1 firefox-esr security update
Debian DSA Debian DSA DSA-6533-1 firefox-esr security update
Debian DSA Debian DSA DSA-6536-1 thunderbird security update
History

Tue, 06 Oct 2026 12:15:00 +0000

Type Values Removed Values Added
Weaknesses CWE-825
References
Metrics threat_severity

None

 threat_severity

Important

Mon, 05 Oct 2026 14:00:00 +0000

Type Values Removed Values Added
First Time appeared Mozilla thunderbird
CPEs cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:*
Vendors & Products Mozilla thunderbird

Wed, 30 Sep 2026 17:45:00 +0000

Type Values Removed Values Added
Description Use-after-free in the Layout: Text and Fonts component. This vulnerability was fixed in Firefox ESR 153.4, Thunderbird 157, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17. Use-after-free in the Layout: Text and Fonts component. This vulnerability was fixed in Firefox ESR 153.4, Thunderbird 157, Thunderbird 140.17, Thunderbird 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17.
References

Wed, 30 Sep 2026 17:30:00 +0000

Type Values Removed Values Added
Description Use-after-free in the Layout: Text and Fonts component. This vulnerability was fixed in Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17. Use-after-free in the Layout: Text and Fonts component. This vulnerability was fixed in Firefox ESR 153.4, Thunderbird 157, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17.
References

Tue, 29 Sep 2026 16:45:00 +0000

Type Values Removed Values Added
First Time appeared Mozilla
Mozilla firefox
Vendors & Products Mozilla
Mozilla firefox

Tue, 29 Sep 2026 15:30:00 +0000

Type Values Removed Values Added
Weaknesses CWE-416
Metrics cvssV3_1

{'score': 8.8, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H'}

ssvc

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

Tue, 29 Sep 2026 13:15:00 +0000

Type Values Removed Values Added
Description Use-after-free in the Layout: Text and Fonts component. This vulnerability was fixed in Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17.
Title Use-after-free in the Layout: Text and Fonts component
References

Subscriptions

Mozilla Firefox Thunderbird
cve-icon MITRE

Status: PUBLISHED

Assigner: mozilla

Published:

Updated: 2026-09-30T17:20:25.663Z

Reserved: 2026-09-26T19:17:03.000Z

Link: CVE-2026-100784

cve-icon Vulnrichment

Updated: 2026-09-29T14:40:29.931Z

cve-icon NVD

Status : Analyzed

Published: 2026-09-29T13:17:43.357

Modified: 2026-10-05T13:43:28.390

Link: CVE-2026-100784

cve-icon Redhat

Severity : Important

Publid Date: 2026-09-29T12:36:09Z

Links: CVE-2026-100784 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-10-07T07:30:14Z

Weaknesses