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Fencer Vulns
medium 5.9

CVE-2026-85534 json

Libsoup: libsoup: http/2 client crash in on_data_source_read_callback when settings initial_window_size shrinks during deferred body read

published 2026-09-04 2 mo ago modified 2026-11-06 3 d ago also EUVD-2026-70997

cvss
5.9
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 24%
public exploits
0
none known

Summary

A flaw was found in libsoup. When a client sends an HTTP/2 request body from a non-pollable input stream, the library can buffer more data than the current flow-control window later allows. A malicious HTTP/2 server can shrink SETTINGS_INITIAL_WINDOW_SIZE while that buffered read is still in progress. The client then copies the full buffer into a smaller DATA callback without a runtime bounds check, which can abort the process or fail the HTTP/2 session.

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
  • libsoup3 Ubuntu Pro 22.04 LTS 3.0.7-0ubuntu1+esm9

ubuntu advisories UBUNTU-CVE-2026-85534

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

  • libsoup SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 3.6.6-160000.4.1
  • libsoup SLES for SAP 15 SP5, SLES for SAP 15 SP4, SLES 15 SP5-LTSS +5 more 3.0.4-150400.3.49.1
  • libsoup SLES for SAP 15 SP6, SLES 15 SP6-LTSS, SLE Module for Basesystem 15 SP7 3.4.4-150600.3.53.1
  • libsoup Linux Micro 6.0 3.4.2-18.1
  • libsoup Linux Micro 6.1 3.4.4-slfo.1.1_11.1

suse advisories SUSE-SU-2026:23848-1SUSE-SU-2026:23857-1SUSE-SU-2026:23866-1SUSE-SU-2026:4274-1SUSE-SU-2026:4273-1SUSE-SU-2026:23875-1

  • libsoup openSUSE Leap 16.0 3.6.6-160000.4.1
  • libsoup openSUSE Tumbleweed 3.6.6-9.1

opensuse advisories openSUSE-SU-2026:21901-1openSUSE-SU-2026:11823-1

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-2026-85534 updated cvss 5.9

libsoup: libsoup: HTTP/2 client crash in on_data_source_read_callback when SETTINGS INITIAL_WINDOW_SIZE shrinks during deferred body read

  • Red Hat Enterprise Linux 10 libsoup3 3.6.6-1.el10
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Enterprise Linux 6 libsoup Red Hat Enterprise Linux 7 libsoup Red Hat Enterprise Linux 8 libsoup Red Hat Enterprise Linux 9 libsoup
    not affected: vulnerable code not present

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
none
Automatable
no
Technical impact
partial
Assessed
2 mo ago

Exploit prediction

0.32% chance of exploitation in the next 30 days, higher than 24% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

  • Red Hat Red Hat Enterprise Linux 10
  • Red Hat Red Hat Enterprise Linux 6
  • Red Hat Red Hat Enterprise Linux 7
  • Red Hat Red Hat Enterprise Linux 8
  • Red Hat Red Hat Enterprise Linux 9

Classification

Weakness

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.