# CVE-2026-77680: Libsoup3: libsoup: quadratic cpu denial of service in http range coalescing after cve-2025-32907 fix

Status: published. Published: 2026-08-25. Updated: 2026-11-06.

An algorithmic complexity flaw exists in libsoup's HTTP Range header processing that persists after the CVE-2025-32907 fix.

CVE-2025-32907 addressed memory amplification when a client repeated the same range many times in a single Range header. Commit 9bb92f7a corrected merge correctness in soup_message_headers_get_ranges_internal() in libsoup/soup-message-headers.c, but the coalescing loop still removes merged ranges using g_array_remove_index() for each coalesced element. Because GArray is contiguous, each mid-array removal performs an O(N) memmove. When many identical satisfiable ranges are supplied (for example bytes=0-0 repeated thousands of times), the loop performs O(N²) work coalescing them into a single range.

The vulnerable path is reachable server-side from handle_partial_get() in libsoup/server/http1/soup-server-message-io-http1.c when a SoupServer handler returns HTTP 200 with a non-empty body. No authentication is required. The number of ranges is bounded only by the maximum request header size (~100 KiB), allowing roughly 25,000 ranges per request. Reporter measurements on libsoup HEAD containing the CVE-2025-32907 fix show ~90 ms single-core CPU per such request at the wire maximum, blocking the server's event loop for that duration.

This is a CPU exhaustion / availability issue only. No memory corruption or information disclosure occurs.

Affected: libsoup versions containing the CVE-2025-32907 fix but not merge request !550.
Fixed upstream: MR !550 merged 2026-08-20, replacing per-element removal with O(N) in-place compaction and rejecting Range headers requesting more than 200 ranges.
Upstream report: https://gitlab.gnome.org/GNOME/libsoup/-/issues/538
Related: CVE-2025-32907

## Remediation

- workaround: Upgrade to a libsoup version containing merge request !550 (O(N) range coalescing and 200-range limit). Until patched, restrict network access to services using SoupServer, or terminate connections that send Range headers with excessive range counts. (source: CNA: redhat)

## Affected products and versions

- Red Hat / Red Hat Enterprise Linux 10 (libsoup3): Version range not reported. Source: CNA: redhat

## Severity and prioritization

- CVSS 3.1: 5.3 (medium); CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L; source: CNA: redhat

- CISA KEV: No listing in collected sources

- EPSS: 0.34% as of 2026-11-05; percentile 28.07%

- SSVC: exploitation poc; automatable yes; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-407

## Exploit evidence

- exploit: https://gitlab.gnome.org/GNOME/libsoup/-/issues/538 (ADP: CISA-ADP)

## References

- https://access.redhat.com/security/cve/CVE-2025-32907 (CNA: redhat; technical-description, x_refsource_REDHAT)

- https://access.redhat.com/security/cve/CVE-2026-77680 (CNA: redhat; vdb-entry, x_refsource_REDHAT)

- https://bugzilla.redhat.com/show_bug.cgi?id=2520892 (CNA: redhat; issue-tracking, x_refsource_REDHAT)

- https://gitlab.gnome.org/GNOME/libsoup/-/issues/538 (CNA: redhat)

- https://gitlab.gnome.org/GNOME/libsoup/-/merge_requests/550 (CNA: redhat)

- https://gitlab.gnome.org/GNOME/libsoup/-/issues/538 (ADP: CISA-ADP; exploit)

## Provenance

- CNA: redhat: https://www.cve.org/CVERecord?id=CVE-2026-77680; retrieved 2026-11-06; source updated 2026-11-06

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-77680; retrieved 2026-11-06; source updated Not reported

Revision: f4c6a008ce5de536224c5c0d31c936b8c8c1ea8dc3096c8aa21f632258c37661

Canonical: https://y2.dev/cve/CVE-2026-77680

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