CVE-2026-6766 | Incorrect boundary conditions in the Libraries component in NSS

Incorrect boundary conditions in the Libraries component in NSS. 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-2026-6766 is rated Low Risk (33.3/100): CVSS High severity, with low exploitation likelihood (EPSS 0.03%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

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-2026-6766

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 2026-04-22 — 0.03% —

Full EPSS history (1 record total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-6766

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N 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:N)
Data isn’t meaningfully altered or forged.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 3.6 134c704f-9b21-4f2e-91b3-4a467353bcc0

Weakness enumeration for CVE-2026-6766

GitHub Security Advisory for CVE-2026-6766

GHSA-q6qg-6fmg-jjcv · Severity: high — Incorrect boundary conditions in the Libraries component in NSS. This vulnerability was fixed in...

OS Trackers for CVE-2026-6766

vendor priority summary link
debian not yet assigned CVE-2026-6766 not yet assigned priority: Debian including 4 source packages (firefox, firefox-esr, nss, thunderbird), 16 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 14, open 2. https://security-tracker.debian.org/tracker/CVE-2026-6766
redhat medium — https://access.redhat.com/security/cve/CVE-2026-6766
ubuntu medium CVE-2026-6766 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-2026-6766

Affected software / configurations for CVE-2026-6766

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

References for CVE-2026-6766

cvelogic Threat Intelligence