Bug 2543283

Summary: CVE-2026-102559 libsoup: libsoup: Heap buffer overflow during WebSocket client-frame masking [fedora-all]
Product: [Fedora] Fedora Reporter: Srikanth Balasubramanian <sbalasub>
Component: libsoupAssignee: Gwyn Ciesla <gwync>
Status: NEW --- QA Contact: Fedora Extras Quality Assurance <extras-qa>
Severity: high Docs Contact:
Priority: high    
Version: 44CC: gwync, mclasen, rhughes, rstrode, tpopela
Target Milestone: ---Keywords: Security, SecurityTracking
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Hardware: Unspecified   
OS: Unspecified   
Whiteboard: {"flaws": ["5c112865-4fb6-4790-9d61-b8c5d02bc070"]}
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description Srikanth Balasubramanian 2026-09-29 16:36:59 UTC 
Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.

A heap buffer overflow was found in libsoup's client-side WebSocket frame construction / masking path.

Outgoing frames are built in a GByteArray. For a send payload larger than the array can represent (at/above ~2^31), g_byte_array_sized_new() / append truncated the length while xor_with_mask() still iterated the full attacker-/caller-controlled length, writing past the small allocation during masking.

Fixed by rejecting outgoing payloads above MAX_OUTGOING_PAYLOAD_SIZE both before and after extensions process the payload (commit d7f074f8, libsoup 3.7.3).

References:
https://gitlab.gnome.org/GNOME/libsoup/-/work_items/554 (Bug 7)
https://gitlab.gnome.org/GNOME/libsoup/-/commit/d7f074f8