[Announce] Security advisory: Recently discovered Use After Free issue in QHttp2ProtocolHandler impacts Qt

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Hi,

There is a "Use After Free" vulnerability in Qt's QHttp2ProtocolHandler in the QtNetwork module. This only affects HTTP/2 handling, HTTP handling is not affected by this at all. This happens due to a race condition between how QHttp2Stream uploads the body of a POST request and the simultaneous handling of HTTP error responses. 

This has been assigned the CVE id CVE-2025-5991.

Affected versions: Qt version 6.9.0. This is fixed in 6.9.1.

Impact: This only affects HTTP/2 handling, HTTP handling is not affected by this at all. This happens due to a race condition between how QHttp2Stream uploads the body of a POST request and the simultaneous handling of HTTP error responses.

Vulnerability Score: CVSS v4.0: 2.1

Solution: 

Apply the following patch for Qt 6.9.0 or update to 6.9.1.

6.9: https://download.qt.io/official_releases/qt/6.9/CVE-2025-5999-qtbase-6.9.patch or https://codereview.qt-project.org/c/qt/qtbase/+/646572

Kind regards,
Andy
--
Andy Shaw,
Director, Customer Services - SQS
The Qt Company