CVE-2026-66339: Libsoup: libsoup: proxy credentials leak to destination server via proxy-authorization header in connect tunnels

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-07-24 · updated 2026-08-24
Weakness: CWE-201

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.

Affected products

GNOME libsoup: all versions
Red Hat Enterprise Linux: 6.0, 7.0, 8.0, 9.0, 10.0

References

https://access.redhat.com/security/cve/CVE-2026-66339
https://bugzilla.redhat.com/show_bug.cgi?id=2506951

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