CVE-2026-66339 Red Hat CVE debrief

Who should care

Users of libsoup who rely on HTTP proxies for secure communication may be affected by this vulnerability, potentially leading to unauthorized access to sensitive information. System administrators and security teams responsible for libsoup-based applications should review their configurations and ensure secure communication protocols are in place. Additionally, developers using libsoup in their applications should be aware of this vulnerability and take necessary precautions to mitigate its impact.

Technical summary

The vulnerability occurs when libsoup establishes a CONNECT tunnel through an HTTP proxy. After the tunnel is established, libsoup incorrectly attaches the Proxy-Authorization header to subsequent HTTPS requests sent through the tunnel to the destination server. This allows the destination server to capture proxy credentials, leading to information disclosure. The CVSS score for this vulnerability is 6.5, indicating a medium severity level. The libsoup library is used in various applications, and users should review their dependencies to determine if they are affected.

Defensive priority

Medium priority should be given to patching or mitigating this vulnerability, as it could lead to information disclosure.

Recommended defensive actions

• Apply patches or updates provided by the libsoup maintainers or affected vendors.
• Review and update configurations for libsoup and related components to ensure secure communication.
• Monitor for any suspicious activity related to proxy credentials.
• Review compensating controls for exposed systems while remediation is scheduled and verified.
• Check relevant monitoring, detection, and logs for exposed assets that need extra review.
• Track exceptions, retest remediated assets, and close the item only after evidence is documented.
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up.

Evidence notes

The CVE record was published on 2026-07-24T23:16:52.187Z and was last modified on 2026-07-27T20:37:16.927Z. The NVD entry is currently Awaiting Analysis. This information is based on the provided source corpus and may be subject to change as new evidence emerges. Defenders should verify the affected scope and severity with the official CVE record and NVD entry. The libsoup library is used in various applications, and users should review their dependencies to determine if they are affected.

Official resources