CVE-2026-6766: mozilla firefox
CVSS: 7.5v3.1HighAnalyzed
AliasesUBUNTU-CVE-2026-6766DEBIAN-CVE-2026-6766CGA-jjgg-3m8q-wvh5CGA-x968-xc64-jffpCGA-3gqm-jqrr-hp73CGA-4245-crx4-f5q9
Published 21-04-2026Last modified 26-05-2026
Vulnerability summary
CVE-2026-6766 is a high (CVSS 7.5) vulnerability in mozilla firefox. EPSS estimates a 0.43% chance of exploitation in the next 30 days, higher than 36.2% of scored vulnerabilities.
CVSS score
7.5/10
010
High · v3.1 (CVE.org)EPSS score
0.43%
0%100%
Low · +0.17 pp in 30 daysKEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded
Advisory lineage
Upstream 0 · Downstream 31 · Related 4MGASA-2026-0124OPENSUSE-SU-2026:10610-1OPENSUSE-SU-2026:10626-1OPENSUSE-SU-2026:11373-1RHSA-2026:10757RHSA-2026:10766RHSA-2026:10767RHSA-2026:12285RHSA-2026:13537RHSA-2026:15892RHSA-2026:17477RHSA-2026:17687RHSA-2026:17688RHSA-2026:17689RHSA-2026:17690RHSA-2026:19041RHSA-2026:19131RHSA-2026:19201RHSA-2026:19348RHSA-2026:19461RHSA-2026:19462RHSA-2026:19463RHSA-2026:19464RHSA-2026:19465RHSA-2026:19466RHSA-2026:19467RHSA-2026:19468RHSA-2026:19469RHSA-2026:19542RHSA-2026:19655RHSA-2026:19704CGA-X9WC-H8GM-Q9HR
Timeline
- 21-04-2026PublishedVulnerability first disclosed.
- 26-05-2026Last modifiedVulnerability information updated.
Description
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.
CVSS metrics
4 scores · 4 sources · 1 versionHigh 7.5Preferred score · CVE.org (CNA)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:NSourcesAll 4 agree
- OSV · UbuntuEcosystem advisory · calculated7.5HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
- OSV · DebianEcosystem advisory · calculated7.5HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
- NVDNIST7.5HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
EPSS trend
Probability
0.43%
Chance of exploitation in the next 30 days
Percentile
36%
Versus all other CVEs
30-day change
+0.17 pp
From 0.26% on 21-09-2026
21-09-202621-10-2026
EPSS score0.43%
Known exploited
Compare KEV catalogsNot in any of the 3 tracked catalogs.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root causeAffected systems
Ubuntu8 products
- mozjs102All versions (No fix recorded)
- mozjs115All versions (No fix recorded)
- mozjs38All versions (No fix recorded)
- mozjs52All versions (No fix recorded)
- mozjs68All versions (No fix recorded)
Debian3 products
- firefox-esr< 140.10.0esr-1~deb12u1 | < 140.10.0esr-1~deb13u1 | < 140.10.0esr-1
- nss< 2:3.87.1-1+deb12u3 | < 2:3.110-1+deb13u2 | < 2:3.123-1
- thunderbird< 1:140.10.0esr-1~deb12u1 | < 1:140.10.0esr-1~deb13u1 | < 1:140.10.0esr-1
Chainguard2 products
- firefox< 140.10-r0
- firefox-esr< 140.10-r0
Mozilla2 products
- firefox< 140.10.0 | < 150.0
- thunderbird< 140.10.0
Wolfi1 product
- firefox< 140.10-r0
5 vendors · 16 products
References
10 links- bugzilla.mozilla.org/show_bug.cgi?id=2023207Permissions Required
- www.mozilla.org/security/advisories/mfsa2026-30/Vendor Advisory
- www.mozilla.org/security/advisories/mfsa2026-32/Vendor Advisory
- www.mozilla.org/security/advisories/mfsa2026-33/Vendor Advisory
- www.mozilla.org/security/advisories/mfsa2026-34/Vendor Advisory
