CVE-2026-84137: mozilla firefox Origin Validation Error
CVSS: 9.8v3.1CriticalModified
AliasesUBUNTU-CVE-2026-84137CGA-chgm-r634-976jCGA-g77w-hvmv-cx48CGA-p33m-hqcv-842cCGA-rhwx-484g-xm58
Published 01-09-2026Last modified 03-09-2026
Vulnerability summary
CVE-2026-84137 is a critical (CVSS 9.8) Origin Validation Error vulnerability in mozilla firefox. EPSS estimates a 0.13% chance of exploitation in the next 30 days, higher than 2.2% of scored vulnerabilities.
CVSS score
9.8/10
010
Critical · v3.1 (CVE.org)EPSS score
0.13%
0%100%
Low · 0.00 pp in 30 daysKEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded
Advisory lineage
Upstream 0 · Downstream 10 · Related 9Timeline
- 01-09-2026PublishedVulnerability first disclosed.
- 03-09-2026Last modifiedVulnerability information updated.
Description
Spoofing issue in the DOM: Core & HTML component. This vulnerability was fixed in Firefox 155, Firefox ESR 153.2, Thunderbird 155, and Thunderbird 153.2.
CVSS metrics
3 scores · 3 sources · 1 versionCritical 9.8Preferred score · CVE.org (CNA)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:HSources3 sources · 4.3–9.8
- OSV · UbuntuEcosystem advisory · calculated9.8CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- NVDNIST4.3MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:NDiffers
EPSS trend
Probability
0.13%
Chance of exploitation in the next 30 days
Percentile
2%
Versus all other CVEs
30-day change
0.00 pp
From 0.13% on 19-09-2026
19-09-202619-10-2026
EPSS score0.13%
Known exploited
Compare KEV catalogsNot in any of the 3 tracked catalogs.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root cause- CWE-346Origin Validation ErrorThe product does not properly verify that the source of data or communication is valid.
- CWE-451User Interface (UI) Misrepresentation of Critical InformationThe user interface (UI) does not properly represent critical information to the user, allowing the information - or its source - to be obscured or spoofed. This is often a component in phishing attacks.
Affected 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)
Chainguard2 products
- firefox< 155.0.1-r0
- firefox-docker-selenium-compat< 155.0.1-r0
Mozilla2 products
- firefox< 153.2.0 | ≥ 154.0.0, < 155.0.0
- thunderbird< 153.2.0 | ≥ 154.0, < 155.0
Wolfi2 products
- firefox< 155.0.1-r0
- firefox-docker-selenium-compat< 155.0.1-r0
4 vendors · 14 products
References
8 links- www.mozilla.org/security/advisories/mfsa2026-82/Vendor Advisory
- www.mozilla.org/security/advisories/mfsa2026-85/Vendor Advisory
- www.mozilla.org/security/advisories/mfsa2026-86/Vendor Advisory
- www.mozilla.org/security/advisories/mfsa2026-88/Vendor Advisory