CVE-2026-41431CWE-347

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

High · published May 11, 2026

CVSS v3.1
8.0
EPSS
0%
Percentile
18.6
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v3.1
8.0 · HIGH
Vector
CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H
CVSS v4.0
Not supplied
EPSS
0.00273 · 18.6th percentile
Weakness
CWE-347 · Improper Verification of Cryptographic Signature
Published
2026-05-11T16:55Z
EPSS history
Timeline
  • 11 MAY 16:55Z
    Zen Browser MAR updater ships with signature verification removed — unsigned updates accepted
    cvelistv5