Bug 2506950 (CVE-2026-66338)

Summary: CVE-2026-66338 libsoup: libsoup: HTTP Request Smuggling via permissive chunk-size parsing in soup_body_input_stream_read_chunked()
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: low    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
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OS: Linux   
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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.
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Description OSIDB Bzimport 2026-07-24 22:29:40 UTC 
The chunked transfer encoding parser in libsoup uses strtoul(metabuf, NULL, 16) to parse chunk sizes without strict validation. This function silently accepts inputs that violate RFC 9112 ยง7.1, including leading whitespace, + prefixes, and trailing invalid characters (e.g., 0z parses as 0). When libsoup operates behind a strict frontend proxy, this parsing differential enables an attacker to smuggle HTTP requests through the backend connection. Both server-side (SoupServer) and client-side chunked response parsing are affected. This is distinct from CVE-2026-1801 which covers bare LF tolerance.

Upstream report: https://gitlab.gnome.org/GNOME/libsoup/-/work_items/533
PSIRTSUPT: https://redhat.atlassian.net/browse/PSIRTSUPT-17666