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.

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Fixes

Solution

No solution given by the 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.

History

Fri, 04 Sep 2026 15:45:00 +0000

Type Values Removed Values Added
First Time appeared Gnome
Gnome libsoup
Vendors & Products Gnome
Gnome libsoup

Fri, 04 Sep 2026 12:15:00 +0000

Type Values Removed Values Added
References
Metrics threat_severity

None

threat_severity

Moderate


Fri, 04 Sep 2026 10:30:00 +0000

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'}


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cve-icon MITRE

Status: PUBLISHED

Assigner: redhat

Published:

Updated: 2026-09-04T16:07:27.046Z

Reserved: 2026-09-04T08:57:22.995Z

Link: CVE-2026-85534

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-09-04T11:17:19.627

Modified: 2026-09-04T16:18:18.770

Link: CVE-2026-85534

cve-icon Redhat

Severity : Moderate

Publid Date: 2026-09-03T00:00:00Z

Links: CVE-2026-85534 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-09-04T15:20:07Z

Weaknesses