CVE-2025-6338 Possible denial of service with multiple incoming connections to a Schannel based server with a TLS backend
An attacker can cause a denial of service on Windows Schannel-based servers by exploiting incomplete cleanup in Qt Network's TLS backend.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2025-6338?
CVE-2025-6338 is a critical denial of service vulnerability in Qt, published on 16 Oct 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
There is an incomplete cleanup vulnerability in Qt Network's Schannel support on Windows which can lead to a Denial of Service over a long period.
This issue affects Qt from 5.15.0 through 6.8.3, from 6.9.0 before 6.9.2.
Weakness: CWE-459
Which versions are affected by CVE-2025-6338?
How do I fix CVE-2025-6338?
No fix has been published for CVE-2025-6338 yet. Limit exposure of the affected software until one is available.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2025-6338 being exploited?
There is no known exploitation of CVE-2025-6338 in the wild and no public exploit code.
Sources
Also known as GHSA-m4hj-jpxf-jhjp.