CVE-2025-38566

In the Linux kernel, the following vulnerability has been resolved:

sunrpc: fix handling of server side tls alerts

Scott Mayhew discovered a security exploit in NFS over TLS in tls_alert_recv() due to its assumption it can read data from the msg iterator's kvec..

kTLS implementation splits TLS non-data record payload between the control message buffer (which includes the type such as TLS aler or TLS cipher change) and the rest of the payload (say TLS alert's level/description) which goes into the msg payload buffer.

This patch proposes to rework how control messages are setup and used by sock_recvmsg().

If no control message structure is setup, kTLS layer will read and process TLS data record types. As soon as it encounters a TLS control message, it would return an error. At that point, NFS can setup a kvec backed msg buffer and read in the control message such as a TLS alert. Msg iterator can advance the kvec pointer as a part of the copy process thus we need to revert the iterator before calling into the tls_alert_recv.

A remotely reachable flaw in the SUNRPC NFS-over-TLS server could allow a client to trigger a kernel crash by sending a crafted TLS alert. The issue lies in how the kernel processes TLS control messages, which can lead to use-after-free or invalid memory accesses during alert handling.

The attack vector is network-based (AV:N), but the required privileges vary with deployment: in many configurations, a client must already possess valid credentials or a certificate to establish an NFS/TLS session, which corresponds to PR:L in CVSS. If the server is configured to accept connections without strict authentication, exploitation could occur with PR:N, but the more common and realistic scenario is PR:L.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

To mitigate this issue, prevent module sunrpc from being loaded. Please see https://access.redhat.com/solutions/41278 for how to blacklist a kernel module to prevent it from loading automatically.