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Fencer Vulns
medium 5.3

CVE-2026-77680 json

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

published 2026-08-25 2 mo ago modified 2026-11-06 3 d ago also EUVD-2026-66111

cvss
5.3
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 42%
public exploits
0
none known

Summary

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

Patch / fix

  • libsoup3 Ubuntu 24.04 LTS 3.4.4-5ubuntu0.9
  • libsoup3 Ubuntu 26.10 3.6.6-1ubuntu3
  • libsoup3 Ubuntu 26.04 LTS 3.6.6-1ubuntu0.1
  • libsoup2.4 Ubuntu 22.04 LTS 2.74.2-3ubuntu0.9
  • libsoup2.4 Ubuntu 24.04 LTS 2.74.3-6ubuntu1.9
  • libsoup3 Ubuntu Pro 22.04 LTS 3.0.7-0ubuntu1+esm9
  • libsoup2.4 Ubuntu Pro 16.04 LTS 2.52.2-1ubuntu0.3+esm8
  • libsoup2.4 Ubuntu Pro 18.04 LTS 2.62.1-1ubuntu0.4+esm9

ubuntu advisories UBUNTU-CVE-2026-77680

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • libsoup2 SLES for SAP 15 SP5, SLES for SAP 15 SP4, SLES 15 SP5-LTSS +8 more 2.74.3-150400.3.43.1
  • libsoup2 SLES for SAP 15 SP6, SLES 15 SP6-LTSS, SLE Module for Basesystem 15 SP7 2.74.3-150600.4.42.1

suse advisories SUSE-SU-2026:4739-1SUSE-SU-2026:4703-1

  • libsoup2 openSUSE Tumbleweed 2.74.3-23.1

opensuse advisories openSUSE-SU-2026:11860-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-77680 updated cvss 5.3

libsoup3: libsoup: quadratic CPU denial of service in HTTP Range coalescing after CVE-2025-32907 fix

  • Red Hat Enterprise Linux 10 libsoup3
    affected: workaround, no fix available “Fix deferred”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
yes
Technical impact
partial
Assessed
2 mo ago

Exploit prediction

0.50% chance of exploitation in the next 30 days, higher than 42% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • gitlab.gnome.org https://gitlab.gnome.org/GNOME/libsoup/-/issues/538 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Affected products

  • Red Hat Red Hat Enterprise Linux 10

Classification

Weakness
  • CWE-407 Inefficient Algorithmic Complexity

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.