Quick answers
- Is CVE-2026-85534 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-85534 being exploited in the wild.
- How severe is CVE-2026-85534?
- Medium severity, with a CVSS score of 5.9, published 4 September 2026.
- Which products and versions are affected?
- Gnome Libsoup 3.0.0 and later.
- Is there a fix for CVE-2026-85534?
- No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
- How is CVE-2026-85534 attacked?
- It is attacked over the network.
- Am I affected by CVE-2026-85534?
- Check whether you run Gnome Libsoup at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
Technical details
A buffer overflow vulnerability exists in libsoup's HTTP/2 implementation (on_data_source_read_callback) when handling request bodies from non-pollable input streams (e.g., GFileInputStream). The flaw occurs when a malicious HTTP/2 server shrinks the SETTINGS_INITIAL_WINDOW_SIZE parameter while a buffered read is in progress. The client then attempts to copy the full buffer into a smaller DATA callback without runtime bounds validation, causing an assertion failure (CWE-617). The vulnerability requires a client to initiate an HTTP/2 request body upload to an attacker-controlled server. In Red Hat builds with assertions enabled, this results in process abort rather than memory corruption. The vulnerability affects libsoup 3.0.0 and later versions.
Affected products
- GNOME libsoup 3.0.0 and later
Timeline
- 2026-09-04: disclosed