Executive brief
Microsoft QUIC is a protocol implementation used to establish secure network connections. This vulnerability allows an attacker on the network to send specially crafted packets that exploit a memory management flaw in path migration logic, leading to arbitrary code execution on the target system. No authentication is required, making this a critical risk for any exposed service using the affected QUIC library.
Technical details
This is a use-after-free (CWE-416) vulnerability in Microsoft QUIC's path migration handling. The root cause occurs in the interaction between QuicConnReplaceRetiredCids (called during NEW_CONNECTION_ID frame processing) and QuicConnRecvPostProcessing. When QuicConnReplaceRetiredCids invokes QuicPathRemove, it frees a network path; however, QuicConnRecvPostProcessing subsequently attempts to promote that same path into Paths[0] without verifying it is still valid, resulting in a use-after-free. An unauthenticated attacker can trigger this via incoming packets over the network. Successful exploitation leads to arbitrary code execution. The fix adds an InUse check before path promotion to guard against referencing freed memory. Patches are available in versions 2.4.19, 2.5.10 and later.
Affected products
- Microsoft Microsoft.Native.Quic.MsQuic.OpenSSL >= 2.5.3, < 2.5.10; < 2.4.19
- Microsoft Microsoft.Native.Quic.MsQuic.Schannel >= 2.5.3, < 2.5.10; < 2.4.19
Timeline
- 2026-08-11: disclosed: Vulnerability published in GitHub Advisory Database
- 2026-08-11: patched: Patches released: versions 2.4.19 and 2.5.10
- 2026-09-08: advisory: Advisory updated and published to GitHub Advisory Database