CVE-2026-85534
A flaw was found in libsoup
- Risk score
- 45/100
- CVSS
- 5.9 v3.1
- Exploit chance (30 days)
- 0.3%
- Published
- 4 Sep 2026
Open in the live forecast Today's forecast
What to know
- What it is
- 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 …
- Affected
- Canonical Ubuntu Linux
- Fix
- Apply the vendor's security update; see the linked advisory.
- Exploitation
- No known exploitation
Why it is Yellow
- CVSS 5.9 medium
- Named in a government or vendor bulletin
Government and vendor bulletins
References
- https://ubuntu.com/security/notices/USN-8890-2
- https://access.redhat.com/security/cve/CVE-2026-85534
- https://bugzilla.redhat.com/show_bug.cgi?id=2528440
- 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
Original 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.
Last activity 21 Oct 2026. Patch Forecast updates every hour.