CVE-2026-89968
HighCVSS 7.5Summary
A vulnerability was found in the Linux kernel's nvmet-tcp subsystem. The NVMe-over-TCP target accepts unsolicited H2CData PDUs without checking whether an R2T was sent for the command. A remote attacker can exploit this to cause a double-add of the command to the response list, leading to a system hang (soft-lockup) or kernel panic (kernel BUG).
Risk Assessment
The vulnerability allows a remote, unauthenticated attacker to cause a denial of service (DoS) in environments with NVMe-over-TCP enabled and allow_any_host mode. This can disrupt critical services relying on this technology.
Recommendation
Apply the Linux kernel patch that rejects unsolicited H2CData PDUs before R2T transmission. If the patch is unavailable, restrict access to the NVMe-over-TCP service to trusted hosts only or temporarily disable this feature.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: nvmet-tcp: reject unsolicited H2CData PDUs nvmet_tcp_handle_h2c_data_pdu() accepts an H2CData PDU after only checking that its TTAG is a valid in-range command index and that the command's data buffers are mapped. It never checks that the target has actually solicited that data by sending an R2T for the command. A remote host can abuse this. It submits a write command that takes the R2T path and, before the target transmits the R2T, sends an H2CData PDU for that command's tag. The data completes the command early, and when the command then fails synchronously (e.g. a length mismatch caught by nvmet_check_transfer_len()), it is completed a second time. Each completion calls nvmet_tcp_queue_response(), so the same command is added to queue->resp_list twice while it is still linked; the second llist_add() makes the node point to itself (lentry->next == lentry). nvmet_tcp_process_resp_list() then walks that self-referential node and adds the command to resp_send_list twice. With CONFIG_DEBUG_LIST this trips the "list_add double add" check (kernel BUG); without it the loop never terminates and the nvmet_tcp workqueue wedges (soft-lockup). It is remotely triggerable and needs no authentication on an allow_any_host subsystem. Track whether an R2T has been transmitted for a command and reject an H2CData PDU that arrives before it. The flag is cleared on command reuse (nvmet_tcp_get_cmd() zeroes cmd->flags) and stays set across the multiple H2CData PDUs of a single solicited transfer.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS