CVE-2026-121039 and is rated Medium severity with a CVSS score of 5.3. It is not in the current CISA KEV record we collected. That does not prove exploitation has not occurred.
What to do next
Remediation and response
Microsoft Security Response Center guidance
Vendor revision: Nov 5, 2026
Release Notes
Vendor-listed releases
157.0.4341.42
CISA KEVNot listedBased on the latest collected catalog
EPSS0.1%Estimated 30-day exploitation probability
Ransomware useNot markedCISA KEV ransomware field
Threat actors0Source-linked actor relationships
Overview
What is CVE-2026-121039?
Incorrect authorization in Proxy Auth in Google Chrome prior to 157.0.8103.38 allowed an adjacent attacker to obtain sensitive information via crafted network traffic. (Chromium security severity: Medium)