CVE-2026-64535 nvmet-tcp: Fix potential UAF when ddgst mismatch
A use-after-free vulnerability in the Linux kernel's NVMe/TCP driver allows attackers to cause denial of service or potentially execute code when data digest mismatches occur.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-64535?
CVE-2026-64535 is a critical use after free vulnerability in Linux, published on 27 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-415
Which versions are affected by CVE-2026-64535?
How do I fix CVE-2026-64535?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-64535 being exploited?
There is no known exploitation of CVE-2026-64535 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-64535, DEBIAN-CVE-2026-64535, GHSA-5wfv-mpg7-6vcr, ROOT-OS-DEBIAN-12-CVE-2026-64535, UBUNTU-CVE-2026-64535.