CVE intelligence

CVE-2026-66339

Vulnerability intelligence

Published Jul 24, 2026Sources checked Oct 27, 2026

6.5MEDIUMCVSS out of 10

What this means

Review the available evidence

CVE-2026-66339 and is rated Medium severity with a CVSS score of 6.5. 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

Ubuntu Security Notices guidance

Vendor revision: Oct 21, 2026

USN-8890-1 fixed vulnerabilities in libsoup.

Microsoft Security Response Center guidance

Vendor revision: Sep 24, 2026

Release Notes

CISA KEVNot listedBased on the latest collected catalog

EPSS0.2%Estimated 30-day exploitation probability

Ransomware useNot markedCISA KEV ransomware field

Threat actors0Source-linked actor relationships

Overview

What is CVE-2026-66339?

A flaw was found in libsoup. After a CONNECT tunnel is established through an HTTP proxy, libsoup incorrectly attaches the Proxy-Authorization header to subsequent HTTPS requests sent through that tunnel to the destination server.

This allows the destination server to capture proxy credentials, leading to information disclosure.

Source: NVD