Medium [CVE-2026-64535] Fix potential UAF when ddgst mismatch
This medium-severity Red Hat Linux advisory covers CVE-2026-64535 affecting Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9.
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Summary
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 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. A use-after-free flaw was found in the Linux kernel's NVMe-over-Fabrics TCP target (nvmet-tcp) driver.
This use-after-free and reference-count underflow can crash the kernel (denial of service) when a remote NVMe/TCP initiator triggers a digest mismatch against a host configured as an NVMe/TCP target.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · high-confidence parse· fetched 8 days ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · high-confidence parse· fetched 8 days ago·verify at source
Mitigation checklist
- There is no mitigation for this issue other than applying the kernel update once available. Because Red Hat does not support and does not enable the nvmet-tcp target functionality by default, systems that have not been explicitly configured with nvmetcli to act as an NVMe-over-Fabrics TCP target are not exposed and require no immediate action. Administrators who have deliberately configured an NVMe/TCP target using this unsupported functionality should restrict network access to the target port to trusted initiators on the same storage network only, and should consider disabling NVMe/TCP data digest or migrating off nvmet-tcp given its unmaintained status, until the fix is applied.
Official advisory · high-confidence parse· fetched 8 days ago·verify at source
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