CVE-2026-66339: A flaw was found in libsoup

Routine

MEDIUM 6.5WATCHLISTMITIGATEMITIGATE

CVE-2026-66339 is a medium-severity flaw (CVSS 6.5) affecting libsoup, enterprise linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

Public exploit reference
On your watchlist

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	6.5 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.2% (top 84%)
CISA exploited list	No
Weakness	CWE-201
Published	2026-07-24
Last modified	2026-08-24

Publisher (CNA): Red Hat, Inc. · Vendor: gnome · redhat

Last updated 2026-08-24 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-24 23:16 UTCPublished CVE record published
2026-08-24 16:44 UTCUpdated Record last modified

gnome libsoup MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy libsoup || rpm -q libsoup || libsoup --version

No fixed or unaffected release known

Apply the vendor mitigation from the advisory, disable the affected feature, or restrict network access.

redhat enterprise linux MITIGATE

Affected: 6.0 · 7.0 · 8.0 · 9.0 · 10.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 6.0

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Advisories and coverage

Official advisories

Ubuntu Security Notices: USN-8890-2: libsoup vulnerabilities 2026-10-21
Amazon Linux 2023 ALAS: ALAS2023-2026-3154 (medium): libsoup 2026-10-12

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-66339?

libsoup: mitigate or apply the listed mitigation; enterprise linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2026-66339 being exploited?

CVE-2026-66339 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-66339 affect?

CVE-2026-66339 affects libsoup, enterprise linux. Severity is medium (CVSS 6.5). 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 allo

How urgent is CVE-2026-66339?

Priority 37/100. Public exploit reference; On your watchlist

Related CVEs

CVE-2026-2708 LOW 3.7 MITIGATE MITIGATE A request smuggling vulnerability exists in libsoup's HTTP/1 header parsing logic
CVE-2026-12548 MEDIUM 4.2 MITIGATE MITIGATE A heap out-of-bounds read flaw was found in libsoup
CVE-2026-102560 HIGH 8.6 UPGRADE MITIGATE A flaw was found in libsoup
CVE-2026-102559 HIGH 8.6 UPGRADE MITIGATE A flaw was found in libsoup
CVE-2026-102558 HIGH 8.6 UPGRADE MITIGATE A flaw was found in libsoup

References

← Back to latest CVEs