nvme-tcp: fix NULL pointer dereferences in nvmet_tcp_build_pdu_iovec
CVE: CVE-2026-22998
Component: kernel
CWE: CWE-476
Severity: Moderate
CVSS v3: 6.3/AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
Release date: 2026-01-25T00:00:00+00:00

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

nvme-tcp: fix NULL pointer dereferences in nvmet_tcp_build_pdu_iovec

Commit efa56305908b ("nvmet-tcp: Fix a kernel panic when host sends an invalid H2C PDU length")
added ttag bounds checking and data_offset
validation in nvmet_tcp_handle_h2c_data_pdu(), but it did not validate
whether the command's data structures (cmd->req.sg and cmd->iov) have
been properly initialized before processing H2C_DATA PDUs.

The nvmet_tcp_build_pdu_iovec() function dereferences these pointers
without NULL checks. This can be triggered by sending H2C_DATA PDU
immediately after the ICREQ/ICRESP handshake, before
sending a CONNECT command or NVMe write command.

Attack vectors that trigger NULL pointer dereferences:
1. H2C_DATA PDU sent before CONNECT → both pointers NULL
2. H2C_DATA PDU for READ command → cmd->req.sg allocated, cmd->iov NULL
3. H2C_DATA PDU for uninitialized command slot → both pointers NULL

The fix validates both cmd->req.sg and cmd->iov before calling
nvmet_tcp_build_pdu_iovec(). Both checks are required because:
- Uninitialized commands: both NULL
- READ commands: cmd->req.sg allocated, cmd->iov NULL
- WRITE commands: both allocated

Statement: A NULL-pointer dereference in the NVMe/TCP target path occurs because nvmet_tcp_build_pdu_iovec() can be called when cmd.req.sg and/or cmd.iov are not initialized. A remote host can trigger this by sending an out-of-order H2C_DATA PDU immediately after the ICREQ/ICRESP handshake (e.g., before CONNECT), causing a kernel crash (DoS). Privileges are typically not required beyond network reachability to the NVMe/TCP target.
NVMe/TCP targets are typically deployed inside isolated storage or data-center networks and are not exposed to the public Internet. In practice, exploitation usually requires access to a local or trusted internal network where NVMe/TCP is used for remote memory or storage access over TCP.

Remediation:
For details on how to apply this update, which includes the changes described in this advisory, refer to:

https://access.redhat.com/articles/11258

The system must be rebooted for this update to take effect.
For details on how to apply this update, which includes the changes described in this advisory, refer to:

https://access.redhat.com/articles/11258

The system must be rebooted for this update to take effect.
For details on how to apply this update, which includes the changes described in this advisory, refer to:

https://access.redhat.com/articles/11258

The system must be rebooted for this update to take effect.
For details on how to apply this update, which includes the changes described in this advisory, refer to:

https://access.redhat.com/articles/11258

The system must be rebooted for this update to take effect.
To mitigate this issue, prevent module nvmet-tcp from being loaded. Please see https://access.redhat.com/solutions/41278 for how to blacklist a kernel module to prevent it from loading automatically. By default it is disabled in Red Hat Enterprise Linux and only root user can enable it.