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
- 5.9MediumCVSS base score
- 0.32%Exploitation in 30 daysEPSS · top 75% of all CVEs
- NoKnown exploitednot in CISA's KEV catalog
- NonePublic exploitsnone known yet
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.
Timeline
ID reserved
By redhat
Published
- 2 months later
· 2 months later
Record updated
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| redhatCNA (assigner) | 3.1 | Medium5.9 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H |
| NVDNVD · Awaiting Analysis | 3.1 | Medium5.9 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H |
- EPSS (exploitation in 30 days)
- 0.32% · top 75% of all CVEs (11 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: no · Technical impact: partial
The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 5.9.
Affected products
Red Hat · Red Hat Enterprise Linux 10
All versions: affected
Red Hat · Red Hat Enterprise Linux 6
All versions: unaffected
Red Hat · Red Hat Enterprise Linux 7
All versions: unaffected
Red Hat · Red Hat Enterprise Linux 8
All versions: unaffected
Red Hat · Red Hat Enterprise Linux 9
All versions: unaffected
What to do
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.
References
References4
- https://access.redhat.com/security/cve/CVE-2026-85534 (opens in a new tab)vdb-entryx_refsource_REDHAT
- RHBZ#2528440 (opens in a new tab)issue-trackingx_refsource_REDHAT
- https://gitlab.gnome.org/GNOME/libsoup/-/blob/master/libsoup/http2/soup-client-message-io-http2.c (opens in a new tab)
- https://gitlab.gnome.org/GNOME/libsoup/-/work_items/551 (opens in a new tab)
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- EUVD EUVD-2026-70997 (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://cveledger.app/cve/CVE-2026-85534)Record last updated .