Vulnerability · Published Sep 4, 2026 · Assigned by redhat
CVE-2026-85534Libsoup: libsoup: http/2 client crash in on_data_source_read_callback when settings initial_window_size shrinks during deferred body read
Medium 5.9
In plain English
A medium-severity security flaw in Red Hat Enterprise Linux 10 from Red Hat. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 25% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | libsoup3 | no fix listed | DEBIAN-CVE-2026-85534 |
| Debian:13 | libsoup3 | no fix listed | DEBIAN-CVE-2026-85534 |
| Ubuntu:22.04:LTS | libsoup2.4 | 2.74.2-3ubuntu0.9 | USN-8890-1 |
| Ubuntu:24.04:LTS | libsoup2.4 | 2.74.3-6ubuntu1.9 | USN-8890-1 |
| Ubuntu:24.04:LTS | libsoup3 | 3.4.4-5ubuntu0.9 | USN-8890-1 |
| Ubuntu:24.04:LTS | libsoup3 | 3.4.4-5ubuntu0.9 | UBUNTU-CVE-2026-85534 |
| Ubuntu:26.04:LTS | libsoup3 | 3.6.6-1ubuntu0.1 | USN-8890-1 |
| Ubuntu:26.04:LTS | libsoup3 | 3.6.6-1ubuntu0.1 | UBUNTU-CVE-2026-85534 |
| Ubuntu:26.10 | libsoup3 | 3.6.6-1ubuntu3 | USN-8890-2 |
| Ubuntu:26.10 | libsoup3 | 3.6.6-1ubuntu3 | UBUNTU-CVE-2026-85534 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Red Hat | Red Hat Enterprise Linux 10 | see references |
| Red Hat | Red Hat Enterprise Linux 6 | see references |
| Red Hat | Red Hat Enterprise Linux 7 | see references |
| Red Hat | Red Hat Enterprise Linux 8 | see references |
| Red Hat | Red Hat Enterprise Linux 9 | see references |
Weakness: CWE-617 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
References
- https://access.redhat.com/security/cve/CVE-2026-85534 vdb-entry, x_refsource_REDHAT
- RHBZ#2528440 issue-tracking, x_refsource_REDHAT
- https://gitlab.gnome.org/GNOME/libsoup/-/blob/master/libsoup/http2/soup-client-message-io-http2.c
- https://gitlab.gnome.org/GNOME/libsoup/-/work_items/551