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Vulnerabilities

Vulnerability · CVE-2026-66339

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

Published Jul 24, 2026 · catalog updated Jul 28, 2026 · Red Hat Red Hat Enterprise Linux 10

Last checked Oct 30, 2026. A connected source was read within the last 7 days.

Check if you run it

No confirmed exploitation is on record for CVE-2026-66339. EPSS is 0.25%. Act only if a listed version of Red Hat Red Hat Enterprise Linux 10 is installed.

Gaps on this record

  • No version range is stored. A customer cannot check an installed version against this record.
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.

Same product and reporting

Severity
Medium6.5
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.25%
Remediation
Advisory link
Affected products
vendor Red Hat Red Hat Enterprise Linux 10 · vendor Red Hat Red Hat Enterprise Linux 6 · vendor Red Hat Red Hat Enterprise Linux 7 · vendor Red Hat Red Hat Enterprise Linux 8 · vendor Red Hat Red Hat Enterprise Linux 9

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.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • vendor Red Hat Red Hat Enterprise Linux 10version unspecified
  • vendor Red Hat Red Hat Enterprise Linux 6version unspecified
  • vendor Red Hat Red Hat Enterprise Linux 7version unspecified
  • vendor Red Hat Red Hat Enterprise Linux 8version unspecified
  • vendor Red Hat Red Hat Enterprise Linux 9version unspecified

How to fix CVE-2026-66339

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-66339. EPSS is 0.25%. Act only if a listed version of Red Hat Red Hat Enterprise Linux 10 is installed.

Which versions are affected?

Affected version ranges are not on this record. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-201. EPSS 0.25%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Technology hubs

Ubuntu security

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. Jul 28, 2026 · CVE.org

    Updated

    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.

  2. Oct 21, 2026 · Ubuntu Security Notices

    Detected

    CVE-2026-66339 is listed by USN-8890-2: libsoup vulnerabilities.

Sources

  • CVE.orgVulnerability recordCVE-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 pro

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-66339

    30-day exploitation probability 0.25%

    first.org
  • Ubuntu Security NoticesVendor advisoryCVE-2026-66339

    USN-8890-1 fixed vulnerabilities in libsoup. This update provides the corresponding updates for libsoup3 on Ubuntu 26.10. Original advisory details: It was discovered that libsoup incorrectly handled certain HTTP/2 requests. A remote attacker could possibly use this issue to caus

    ubuntu.com

References

Freshness

Last verified in this catalog Oct 29, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.

  • Ubuntu Security NoticesOct 30, 2026
  • CVE.orgOct 23, 2026
  • FIRST EPSSOct 23, 2026