Executive brief
libsoup is a widely-used HTTP library used in web servers and applications. A flaw in how it processes HTTP Range requests can cause excessive CPU consumption when a client sends a specially-crafted request with thousands of identical range specifications. This can block server processing and cause a denial of service, though no data is exposed or corrupted.
Technical details
An algorithmic complexity vulnerability exists in libsoup's HTTP Range header coalescing logic in soup_message_headers_get_ranges_internal(). The vulnerable code uses g_array_remove_index() in a loop to coalesce identical ranges, which performs O(N) memmove operations for each removal on the contiguous GArray, resulting in O(N²) overall complexity. The flaw is reachable server-side when a SoupServer handler returns HTTP 200 with a non-empty body. No authentication is required. An attacker can send an HTTP request with up to ~25,000 identical ranges (e.g., bytes=0-0 repeated) within the ~100 KiB header size limit, consuming ~90 ms of single-core CPU per request and blocking the server's event loop. The fix, merged in upstream MR !550 (2026-08-20), replaces per-element removal with O(N) in-place compaction and enforces a 200-range limit per request.
Affected products
- GNOME libsoup versions containing CVE-2025-32907 fix but prior to MR !550 (before 2026-08-20)
Timeline
- 2026-08-25: disclosed
- 2026-08-20: patched: MR !550 merged