Description
Use-after-free in the DOM: Core & HTML 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: Potential arbitrary code execution or denial of service via a browser memory corruption exploit
Action: Immediate Patch
AI Analysis

Impact

The updated description indicates a use‑after‑free in the DOM Core & HTML component, leading to memory corruption. An attacker could potentially execute arbitrary code or cause a crash.

Affected Systems

The flaw was fixed in Mozilla Firefox ESR 153.4, Firefox 157, ESR 115.42, and ESR 140.17, as well as Thunderbird 157, Thunderbird 140.17, and Thunderbird 153.4. All earlier versions of Firefox and Thunderbird, including older stable and extended supported releases, remain vulnerable until one of those patched versions is installed.

Risk and Exploitability

The CVSS score of 8.8 indicates a high severity memory corruption flaw. The EPSS score indicates an exploitation probability of less than 1 %, meaning the risk of exploitation is low but nonzero. The vulnerability is not listed in CISA KEV, implying no confirmed exploits to date. The likely attack vector is remote, via a malicious web page or HTML content that the user views or downloads, so if successfully exploited the flaw could lead to system compromise or denial of service. Users should assess the likelihood relative to their current Firefox version and apply the available patch promptly.

Generated by OpenCVE AI on October 7, 2026 at 07:58 UTC.

Remediation

No solution or workaround provided in the CVE record.

OpenCVE Recommended Actions

  • Apply the latest Thunderbird update, ensuring installation of at least Thunderbird 157 or the corresponding ESR release (140.17, 153.4).
  • Apply the latest Firefox update, ensuring installation of at least Firefox 157 or the corresponding ESR release (115.42, 140.17, or 153.4).
  • If immediate update is not possible, reconfigure Firefox to disable scripts or use a hardened user profile that limits access to untrusted sources.
  • Regularly check for and install future Firefox and Thunderbird security updates from Mozilla’s official channels to maintain protection against similar memory corruption vulnerabilities.

Generated by OpenCVE AI on October 7, 2026 at 07:58 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

Mon, 19 Oct 2026 15:45:00 +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

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

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

None

 threat_severity

Important

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

Type Values Removed Values Added
Description Use-after-free in the DOM: Core & HTML 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 DOM: Core & HTML 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 DOM: Core & HTML 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 DOM: Core & HTML 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 17:15:00 +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 DOM: Core & HTML 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 DOM: Core & HTML component
References

Subscriptions

Mozilla Firefox Thunderbird
cve-icon MITRE

Status: PUBLISHED

Assigner: mozilla

Published:

Updated: 2026-09-30T17:20:33.281Z

Reserved: 2026-09-26T19:17:21.137Z

Link: CVE-2026-100791

cve-icon Vulnrichment

Updated: 2026-09-29T14:40:24.935Z

cve-icon NVD

Status : Analyzed

Published: 2026-09-29T13:17:44.133

Modified: 2026-10-19T15:31:43.310

Link: CVE-2026-100791

cve-icon Redhat

Severity : Important

Publid Date: 2026-09-29T12:36:12Z

Links: CVE-2026-100791 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-10-07T08:00:12Z

Weaknesses