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
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.
Fixes and workarounds
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.
Source: CNA: redhatAffected products and versions
| Product | Versions | Authority |
|---|---|---|
| Red Hat Enterprise Linux 10 Red Hat libsoup3
https://access.redhat.com/downloads/content/package-browser/ |
Range not reported
Other versions: affected |
CNA: redhat |
| Red Hat Enterprise Linux 6 Red Hat libsoup
https://access.redhat.com/downloads/content/package-browser/ |
Range not reported
Other versions: unaffected |
CNA: redhat |
| Red Hat Enterprise Linux 7 Red Hat libsoup
https://access.redhat.com/downloads/content/package-browser/ |
Range not reported
Other versions: unaffected |
CNA: redhat |
| Red Hat Enterprise Linux 8 Red Hat libsoup
https://access.redhat.com/downloads/content/package-browser/ |
Range not reported
Other versions: unaffected |
CNA: redhat |
| Red Hat Enterprise Linux 9 Red Hat libsoup
https://access.redhat.com/downloads/content/package-browser/ |
Range not reported
Other versions: unaffected |
CNA: redhat |
Version ranges are source assertions. Check the vendor advisory and your installed configuration before determining exposure.
CVSS assessments
| Version / score | Vector | Authority |
|---|---|---|
| 3.1 / 5.9 medium |
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H | CNA: redhat |
Exploit evidence
No exploit evidence in collected sources. This is not proof of no exploitation.
References
- https://access.redhat.com/security/cve/CVE-2026-85534CNA: redhat · vdb-entry, x_refsource_REDHAT
- https://bugzilla.redhat.com/show_bug.cgi?id=2528440CNA: redhat · issue-tracking, x_refsource_REDHAT
- https://gitlab.gnome.org/GNOME/libsoup/-/blob/master/libsoup/http2/soup-client-message-io-http2.cCNA: redhat
- https://gitlab.gnome.org/GNOME/libsoup/-/work_items/551CNA: redhat
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