CVE-2026-66339 Libsoup: libsoup: proxy credentials leak to destination server via proxy-authorization header in connect tunnels
Attackers can capture proxy credentials when libsoup incorrectly sends Proxy-Authorization headers to destination servers over HTTPS tunnels.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-66339?
CVE-2026-66339 is a medium-severity vulnerability in Redhat Enterprise Linux, published on 24 Jul 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
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.
Weakness: CWE-201
Which versions are affected by CVE-2026-66339?
It affects 2 products.
Products include Gnome Libsoup, Redhat Enterprise Linux.
How do I fix CVE-2026-66339?
Apply the vendor's patch.
Is CVE-2026-66339 being exploited?
There is no known exploitation of CVE-2026-66339 in the wild and no public exploit code.
Other vulnerabilities in Redhat Enterprise Linux
- CVE-2026-102556 Libsoup: libsoup: heap buffer overflow from websocket pong signal type confusion
- CVE-2026-102557 Libsoup: libsoup: heap buffer overflow during websocket message reassembly
- CVE-2026-102558 Libsoup: libsoup: heap buffer overflow during websocket receive-buffer growth
- CVE-2026-102559 Libsoup: libsoup: heap buffer overflow during websocket client-frame masking
- CVE-2026-102560 Libsoup: libsoup: heap buffer overflow during outgoing permessage-deflate buffer growth
Sources
Also known as AZL-94098, DEBIAN-CVE-2026-66339, ECHO-3341-e81d-bf5b, GHSA-vh9q-f797-xwg7, UBUNTU-CVE-2026-66339.