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

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-85534
StatePUBLISHED
Assignerredhat
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-04 11:17:19 UTC
Updated2026-09-04 11:17:19 UTC
DescriptionA 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.

Risk And Classification

Primary CVSS: v3.1 5.9 MEDIUM from [email protected]

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Problem Types: CWE-617 | CWE-617 Reachable Assertion

VersionSourceTypeScoreSeverityVector
3.1[email protected]Primary5.9MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
3.1CNACVSS5.9MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Red Hat Red Hat Enterprise Linux 10 Not specified Not specified
CNA Red Hat Red Hat Enterprise Linux 6 Not specified Not specified
CNA Red Hat Red Hat Enterprise Linux 7 Not specified Not specified
CNA Red Hat Red Hat Enterprise Linux 8 Not specified Not specified
CNA Red Hat Red Hat Enterprise Linux 9 Not specified Not specified

References

ReferenceSourceLinkTags
bugzilla.redhat.com/show_bug.cgi [email protected] bugzilla.redhat.com
gitlab.gnome.org/GNOME/libsoup/-/work_items/551 [email protected] gitlab.gnome.org
access.redhat.com/security/cve/CVE-2026-85534 [email protected] access.redhat.com
gitlab.gnome.org/GNOME/libsoup/-/blob/master/libsoup/http2/soup-client-message... [email protected] gitlab.gnome.org
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: Red Hat would like to thank xtromera for reporting this issue. (en)

Additional Advisory Data

SourceTimeEvent
CNA2026-09-03T17:19:37.253ZReported to Red Hat.
CNA2026-09-03T00:00:00.000ZMade public.

Workarounds

CNA: 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.

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