CVE-2026-62815: Microsoft QUIC use-after-free in path migration

CVE-2026-62815 · Severity: critical · CVSS 9.8 · Published 2026-09-08

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.

Technologies: Microsoft MsQuic, Microsoft.Native.Quic.MsQuic.OpenSSL (NuGet), Microsoft.Native.Quic.MsQuic.Schannel (NuGet). Vendors: Microsoft, NuGet.

Quick answers

Is CVE-2026-62815 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-62815 being exploited in the wild.
How severe is CVE-2026-62815?
Critical severity, with a CVSS score of 9.8, published 8 September 2026.
Which products and versions are affected?
Microsoft MsQuic >= 2.5.3, < 2.5.10; < 2.4.19; Microsoft.Native.Quic.MsQuic.OpenSSL (NuGet) ECOSYSTEM:introduced=2.5.3,fixed=2.5.10; Microsoft.Native.Quic.MsQuic.Schannel (NuGet) ECOSYSTEM:introduced=2.5.3,fixed=2.5.10.
Is there a fix for CVE-2026-62815?
Yes. Microsoft.Native.Quic.MsQuic.OpenSSL (NuGet): upgrade to 2.5.10 or later; Microsoft.Native.Quic.MsQuic.Schannel (NuGet): upgrade to 2.5.10 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-62815 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-62815?
Check whether you run Microsoft MsQuic, Microsoft.Native.Quic.MsQuic.OpenSSL (NuGet) or Microsoft.Native.Quic.MsQuic.Schannel (NuGet) 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.

How to fix

  • Microsoft.Native.Quic.MsQuic.OpenSSL (NuGet): upgrade to 2.5.10 or later
    dotnet add package Microsoft.Native.Quic.MsQuic.OpenSSL --version 2.5.10
  • Microsoft.Native.Quic.MsQuic.Schannel (NuGet): upgrade to 2.5.10 or later
    dotnet add package Microsoft.Native.Quic.MsQuic.Schannel --version 2.5.10

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

Identifiers

  • CVE-2026-62815
  • GHSA-92f5-vc22-8j33

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

References

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