CVE-2026-66338: gnome libsoup HTTP Request/Response Smuggling

Vulnerability summary

CVE-2026-66338 is a high (CVSS 7.2) HTTP Request/Response Smuggling vulnerability in gnome libsoup. EPSS estimates a 0.29% chance of exploitation in the next 30 days, higher than 20.3% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 24-07-2026
   PublishedVulnerability first disclosed.
2. 27-07-2026
   Last modifiedVulnerability information updated.

Description

A flaw was found in libsoup. The chunked transfer encoding parser uses a permissive parsing function for chunk sizes that silently accepts inputs violating RFC 9112, including leading whitespace, plus sign prefixes, and trailing invalid characters. When libsoup operates behind a strict frontend proxy, this parsing differential can be exploited to smuggle HTTP requests.

• CWE-444Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination.