Medium [CVE-2026-15714] Out-of-bounds read in soup_multipart_input_stream_read_headers via an oversized multipart boundary string

An out-of-bounds read vulnerability was found in libsoup's multipart processing subsystem. The flaw exists in the soup_multipart_input_stream_read_headers() function inside soup-multipart-input-stream.c, which does not adequately restrict or validate the size of incoming multipart boundary strings.

When processing a crafted HTTP response containing a malformed or oversized boundary parameter, the internal stream reader reads past the allocated buffer bounds. A remote, unauthenticated attacker can exploit this behavior to cause a service denial (DoS) through application failure or potentially read fragments of unauthorized memory metadata.

This vulnerability presents a moderate risk to confidentiality and availability for software implementations implementing libsoup for multipart payload handling. Because the memory tracking misalignment happens during the automated header ingestion phase, an attacker can seamlessly induce a crash remotely without needing local context or user interaction.

Red Hat Product Security ranks this as a notable security regression within parsing utilities, though impact vectors generally manifest as localized client or server session instability rather than complete remote code execution. Red Hat severity: Moderate — CVSS 6.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L).

Weakness: CWE-125.