Critical Vulnerability: CVE-2026-64535

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

nvmet-tcp: Fix potential UAF when ddgst mismatch

Shivam Kumar found via vulnerability testing:

When data digest is enabled on an NVMe/TCP connection and a digest

mismatch occurs on a non-final H2C_DATA PDU during an R2T-based

data transfer, the digest error handler in nvmet_tcp_try_recv_ddgst()

calls nvmet_req_uninit() — which performs percpu_ref_put() on the

submission queue — but does NOT mark the command as completed. It

does not set cqe->status, does not modify rbytes_done, and does not

clear any flag. When the subsequent fatal error triggers queue

teardown, nvmet_tcp_uninit_data_in_cmds() iterates all commands,

checks nvmet_tcp_need_data_in() for each one, and finds that the

already-uninited command still appears to need data (because

rbytes_done < transfer_len and cqe->status == 0). It therefore calls

nvmet_req_uninit() a second time on the same command — a double

percpu_ref_put against a single percpu_ref_get.

CVE-2026-64535 is rated CRITICAL severity, requiring immediate attention from security teams.

CVSS Base Score: 9.8/10

EPSS (Exploit Prediction): 0.2% probability of exploitation in the next 30 days.

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