Read the docs
TI-2026-30030 Aliases CVE-2026-41431

Zen Browser MAR updater ships with signature verification removed — unsigned updates accepted

Priority HIGH 70CWE-347Published · Updated

Key facts

Attack vector
Network
Privileges required
High
User interaction
None
Attack complexity
High
Impact type
Security bypass
Confidentiality · integrity · availability
High · High · High
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA. Impact type from CWE-347.

Summary

Zen is a firefox-based browser. Prior to 1.19.9b, Zen Browser ships a Mozilla Application Resource (MAR) updater (org.mozilla.updater) that has had all MAR signature verification stripped from the Firefox codebase it was forked from. The MAR files served to users contain zero cryptographic signatures, and the updater binary contains zero cryptographic verification code. This eliminates the defense-in-depth that MAR signing provides. If the update server or GitHub release pipeline is compromised, arbitrary unsigned code can be delivered to all Zen users via the auto-update mechanism. This vulnerability is fixed in 1.19.9b.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00199 9th percentileScored 2026-11-07
Fix Fixed desktop (zen-browser): 1.19.9b

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
Poc
Automatable
No
Technical impact
Total

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
zen-browserdesktopbefore 1.19.9b1.19.9bPatch availableCNA
  • desktop Vendorzen-browser Affected before 1.19.9b Fixed in 1.19.9b Patch available CNA

Remediation

  • Fix · CNA desktop (zen-browser) Fixed in 1.19.9b

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-41431

References

Other 2

  • TI-2026-32978 Zen Browser - Missing Fullscreen Security Notification Allows Origin Spoofing CVSS 4.0MEDIUM 6.3
  • TI-2026-32559 Zen Browser Mac - Address Bar Spoofing via Long Subdomain CVSS 3.1MEDIUM 4.7
  • TI-2026-32558 Zen Browser: RSS Live-Folder Item URLs Are Not Scheme-Restricted Before Trusted Tab Creation CVSS 3.1LOW 2.4
  • TI-2026-41404 Zen: Context-menu "Open link in glance" / "Split link in new tab" loads a page-controlled… CVSS 3.1N/A 0.0

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences