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Fencer Vulns
medium 6.5

CVE-2026-66339 json

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

published 2026-07-24 3 mo ago modified 2026-11-05 3 d ago also EUVD-2026-48751

cvss
6.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 16%
public exploits
0
none known

Summary

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.

Patch / fix

  • libsoup3 Ubuntu 24.04 LTS 3.4.4-5ubuntu0.9
  • libsoup3 Ubuntu 26.10 3.6.6-1ubuntu3
  • libsoup3 Ubuntu 26.04 LTS 3.6.6-1ubuntu0.1
  • libsoup2.4 Ubuntu 22.04 LTS 2.74.2-3ubuntu0.9
  • libsoup2.4 Ubuntu 24.04 LTS 2.74.3-6ubuntu1.9
  • libsoup3 Ubuntu Pro 22.04 LTS 3.0.7-0ubuntu1+esm9
  • libsoup2.4 Ubuntu Pro 16.04 LTS 2.52.2-1ubuntu0.3+esm8
  • libsoup2.4 Ubuntu Pro 18.04 LTS 2.62.1-1ubuntu0.4+esm9

ubuntu advisories UBUNTU-CVE-2026-66339

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • libsoup SLES for SAP applications 16.0, SLES 16.0 3.6.6-160000.5.1
  • libsoup Linux Micro 6.0 3.4.2-159998.1.1
  • libsoup2 SLES for SAP 15 SP5, SLES for SAP 15 SP4, SLES 15 SP5-LTSS +8 more 2.74.3-150400.3.43.1
  • libsoup2 SLES for SAP 15 SP6, SLES 15 SP6-LTSS, SLE Module for Basesystem 15 SP7 2.74.3-150600.4.42.1
  • libsoup SLES for SAP 15 SP6, SLES 15 SP6-LTSS, SLE Module for Basesystem 15 SP7 3.4.4-150600.3.56.1
  • libsoup SLES for SAP 15 SP5, SLES for SAP 15 SP4, SLES 15 SP5-LTSS +5 more 3.0.4-150400.3.52.1
  • libsoup SLES LTSS Extended Security 12 SP5, SLES 12 SP5-LTSS 2.62.2-5.49.1

suse advisories SUSE-SU-2026:24470-1SUSE-SU-2026:24368-1SUSE-SU-2026:4739-1SUSE-SU-2026:4703-1SUSE-SU-2026:4690-1SUSE-SU-2026:4558-1

  • libsoup openSUSE Tumbleweed 3.8.1-1.1
  • libsoup openSUSE Leap 16.0 3.6.6-160000.5.1
  • libsoup2 openSUSE Tumbleweed 2.74.3-24.1

opensuse advisories openSUSE-SU-2026:12365-1openSUSE-SU-2026:22181-1openSUSE-SU-2026:12084-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-66339 updated cvss 6.5

libsoup: libsoup: Proxy credentials leak to destination server via Proxy-Authorization header in CONNECT tunnels

  • Red Hat Enterprise Linux 6 libsoup Red Hat Enterprise Linux 7 libsoup Red Hat Enterprise Linux 8 libsoup Red Hat Enterprise Linux 9 libsoup Red Hat Enterprise Linux 10 libsoup3
    affected: no fix available “Fix deferred”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
3 mo ago

Exploit prediction

0.25% chance of exploitation in the next 30 days, higher than 16% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • bugzilla.redhat.com https://bugzilla.redhat.com/show_bug.cgi?id=2506951 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N

Affected products

  • Red Hat Red Hat Enterprise Linux 10
  • Red Hat Red Hat Enterprise Linux 6
  • Red Hat Red Hat Enterprise Linux 7
  • Red Hat Red Hat Enterprise Linux 8
  • Red Hat Red Hat Enterprise Linux 9

Classification

Weakness
  • CWE-201 Insertion of Sensitive Information Into Sent Data

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.