CVE-2026-6771 | Mitigation bypass in the DOM: Security component

Mitigation bypass in the DOM: Security component. This vulnerability was fixed in Firefox 150, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10.

Published: 2026-04-21 Last update: 2026-04-22 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-6771 is rated Moderate Risk (45.9/100): CVSS Critical severity, with low exploitation likelihood (EPSS 0.06%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-6771

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-04-27 0.04% 0.06% +0.02%
2 2026-04-22 — 0.04% —

Full EPSS history (2 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-6771

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
9.8 3.1 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 5.9 134c704f-9b21-4f2e-91b3-4a467353bcc0

Weakness enumeration for CVE-2026-6771

GitHub Security Advisory for CVE-2026-6771

GHSA-88fc-5m2g-g6q2 · Severity: critical — Mitigation bypass in the DOM: Security component. This vulnerability was fixed in Firefox 150 and...

OS Trackers for CVE-2026-6771

vendor priority summary link
debian not yet assigned CVE-2026-6771 not yet assigned priority: Debian including 3 source packages (firefox, firefox-esr, thunderbird), 11 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 11. https://security-tracker.debian.org/tracker/CVE-2026-6771
redhat medium — https://access.redhat.com/security/cve/CVE-2026-6771
ubuntu medium CVE-2026-6771 medium priority: Ubuntu including 9 source packages (firefox, mozjs102, …), 49 status rows across 7 suites (bionic, focal, jammy, noble, questing, resolute, upstream): DNE 23, needs-triage 10, ignored 8, not-affected 7, needed 1. https://ubuntu.com/security/CVE-2026-6771

Affected software / configurations for CVE-2026-6771

Vendor Product Version Raw CPE
mozilla firefox < 150.0 cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:*
mozilla firefox >= 140.0, < 140.10.0 cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:*
mozilla thunderbird >= 140.0, < 140.10.0 cpe:2.3:a:mozilla:thunderbird:*:*:*:*:esr:*:*:*

References for CVE-2026-6771

cvelogic Threat Intelligence