CVE-2026-2775
Published: 24 February 2026
Summary
CVE-2026-2775 is a critical-severity Authentication Bypass Using an Alternate Path or Channel (CWE-288) vulnerability in Mozilla Firefox. Its CVSS base score is 9.8 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Drive-by Compromise (T1189); ranked at the 42.1th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 RA-5 (Vulnerability Monitoring and Scanning) and SI-2 (Flaw Remediation).
Deeper analysis
CVE-2026-2775 is a mitigation bypass vulnerability in the DOM HTML Parser component of Mozilla Firefox and Thunderbird. It affects versions of Firefox prior to 148, Firefox ESR prior to 115.33 and 140.8, and Thunderbird prior to 148 and 140.8. The issue is classified under CWE-288 with a CVSS v3.1 base score of 9.8 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H), indicating critical severity due to its potential for high impact across confidentiality, integrity, and availability.
The vulnerability enables exploitation by any remote, unauthenticated attacker with network access and low attack complexity, requiring no user interaction or privileges. Successful exploitation allows the attacker to bypass security mitigations in the HTML parser, potentially leading to arbitrary code execution, data theft, or system compromise within the affected browser or email client context.
Mozilla's security advisories (MFSA 2026-13 through 2026-16) and the associated Bugzilla entry (bug 2015199) confirm the vulnerability was addressed in the listed fixed releases. Security practitioners should prioritize updating to Firefox 148 or later, Firefox ESR 115.33/140.8 or later, and Thunderbird 148/140.8 or later to mitigate the issue.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-8495
Vulnerability details
Mitigation bypass in the DOM: HTML Parser component. This vulnerability was fixed in Firefox 148, Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
CVE describes remote client-side HTML/DOM parser mitigation bypass in browser/email client leading directly to arbitrary code execution (no UI required); maps to drive-by compromise (T1189) as initial access vector and exploitation for client execution (T1203).
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Mandates timely identification, reporting, and patching of flaws like CVE-2026-2775 in Firefox and Thunderbird HTML parser to prevent exploitation.
Requires vulnerability scanning to identify systems running vulnerable versions of Firefox or Thunderbird affected by CVE-2026-2775.
Ensures dissemination of security advisories such as Mozilla MFSA 2026-13 to prompt patching of CVE-2026-2775.
Hardening callouts derived
Configuration rules from DISA STIG baselines that reduce the attack surface for weaknesses of the type cited by this CVE. Derived transitively via CVE→CWE→STIG over `controls_xwalks` (authoritative rows only).
Oracle Linux 8 (2 rules)
- V-248598 There must be no ".shosts" files on the OL 8 operating system. via CWE-288
- V-248827 OL 8 must not have the rsh-server package installed. via CWE-288
Oracle Linux 9 (2 rules)
- V-271757 OL 9 file systems must not contain shosts.equiv files. via CWE-288
- V-271758 OL 9 file systems must not contain .shosts files. via CWE-288
RHEL 7 (3 rules)
- V-204424 The Red Hat Enterprise Linux operating system must not allow accounts configured with blank or null passwords. via CWE-288
- V-204440 Red Hat Enterprise Linux operating systems version 7.2 or newer using Unified Extensible Firmware Interface (UEFI) must require authentication upon booting into single-user and maintenance modes. via CWE-288
- V-204442 The Red Hat Enterprise Linux operating system must not have the rsh-server package installed. via CWE-288