CVE-2026-85534

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

Published Sep 4, 2026 CVSS 3.1 · 5.9 Medium EPSS < 1% KEV · Not listed
Description
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.

Remediation

Vendor Workaround

Do not HTTP/2-upload from non-pollable streams (e.g. GFileInputStream) to untrusted servers. soup_message_set_request_body_from_bytes() is the pollable path. Assertions abort instead of returning an oversized length; that is not a fix.

Tracking

Sign in to view the affected projects.

Advisories

Source ID Title
Ubuntu USN Ubuntu USN USN-8890-1 libsoup vulnerabilities
Ubuntu USN Ubuntu USN USN-8890-2 libsoup vulnerabilities
History
Type Values Removed Values Added
First Time appeared Redhat rhel Els
CPEs cpe:/o:redhat:enterprise_linux:10
cpe:/o:redhat:enterprise_linux:6
cpe:/o:redhat:enterprise_linux:7
cpe:/o:redhat:enterprise_linux:8
cpe:/o:redhat:enterprise_linux:9
cpe:/a:redhat:enterprise_linux:10
cpe:/a:redhat:enterprise_linux:8
cpe:/a:redhat:enterprise_linux:9
cpe:/o:redhat:rhel_els:6
cpe:/o:redhat:rhel_els:7
Vendors & Products Redhat rhel Els
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
First Time appeared Gnome
Gnome libsoup
Vendors & Products Gnome
Gnome libsoup
Type Values Removed Values Added
Description 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.
Title Libsoup: libsoup: http/2 client crash in on_data_source_read_callback when settings initial_window_size shrinks during deferred body read
First Time appeared Redhat
Redhat enterprise Linux
Weaknesses CWE-617
CPEs cpe:/o:redhat:enterprise_linux:10
cpe:/o:redhat:enterprise_linux:6
cpe:/o:redhat:enterprise_linux:7
cpe:/o:redhat:enterprise_linux:8
cpe:/o:redhat:enterprise_linux:9
Vendors & Products Redhat
Redhat enterprise Linux
References
Metrics cvssV3_1

{'score': 5.9, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
redhat
Published
Updated
Nov 6, 2026, 1:08 AM
Reserved
Sep 4, 2026, 8:57 AM
Status
Awaiting Analysis
Published
Sep 4, 2026, 11:17 AM
Modified
Nov 6, 2026, 1:17 AM
Severity
Moderate
Public date
Sep 3, 2026, 12:00 AM