What is CVE-2026-66339?

CVE-2026-66339 is a medium-severity vulnerability in GNOME Libsoup, classified under Insertion of Sensitive Information into Sent Data. CVSS score: 6.5/10. Published 2026-07-24.

How severe is CVE-2026-66339?

Medium severity. CVSS v3 base score is 6.5 out of 10.

Vulnerability in GNOME Libsoup

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.

EPSS: 0.002 (13.3th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N.

Affected products

Gnome Libsoup
Red Hat Enterprise Linux 10
Red Hat Enterprise Linux 6
Red Hat Enterprise Linux 7
Red Hat Enterprise Linux 8
Red Hat Enterprise Linux 9
Redhat Enterprise_linux — versions 10.0, 6.0, 7.0

Weakness classification (CWE)

CWE-201 — Insertion of Sensitive Information into Sent Data

References

secalert@redhat.com (x_refsource_REDHAT, vdb-entry, Vendor Advisory)
secalert@redhat.com (x_refsource_REDHAT, issue-tracking, Exploit, Mitigation, Issue Tracking, Vendor Advisory)

Frequently asked questions

What is CVE-2026-66339?: CVE-2026-66339 is a medium-severity vulnerability in GNOME Libsoup, classified under Insertion of Sensitive Information into Sent Data. CVSS score: 6.5/10. Published 2026-07-24.
How severe is CVE-2026-66339?: Medium severity. CVSS v3 base score is 6.5 out of 10.