CVE-2026-41431

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

CVSS 8 HIGHEPSS 0.2%CWE-347

Vexday Risk Score

21Low

SSVC decision (CISA)

Track

No exploitation signal → monitor

CVSS 8EPSS 0.2%KEV nãoPoC —Nuclei —Metasploit —Patch —

Lifecycle

11 May 2026Published on NVD

Recommendation: Monitor — no exploitation signal at the moment.

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.

CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H

Affected products

zen-browser · desktop

Want to know if your infrastructure is exposed to this?

Talk to TrueHacking →

References

https://github.com/zen-browser/desktop/commit/270db6d6713d2c6c14d9df0b4bc7662843d3d54e https://github.com/zen-browser/desktop/security/advisories/GHSA-qpj9-m8jc-mw6q