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CVE-2026-64535
nvmet-tcp: Fix potential UAF when ddgst mismatch
Published 2026-07-27 (3 months ago) by the Linux kernel CNA. Subsystem drivers/nvme. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-64535 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | fixedDLA-4720-1 · 2026-08-05 · text | 6.1.180-1 | Update the kernel and reboot. DLA-4720-1 shipped the fix on 2026-08-05, in 6.1.180-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6405-1 · 2026-07-31 · text | 6.12.100-1 | Update the kernel and reboot. DSA-6405-1 shipped the fix on 2026-07-31, in 6.12.100-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.3-1 | Update the kernel and reboot. Fixed in 7.1.3-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.3-1 | Update the kernel and reboot. Fixed in 7.1.3-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4724-1 · 2026-08-07 · text | 6.12.100-1~deb12u1 | Update the kernel and reboot. DLA-4724-1 shipped the fix on 2026-08-07, in 6.12.100-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
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.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
drivers/nvme/target/tcp.c
- What this is
- NVM EXPRESS TARGET DRIVERMAINTAINERS section matched on drivers/nvme/target/ · linux-nvme@lists.infradead.org · Supported
- Kernel module
- nvmet_tcp
Check it on the machine
grep -w CONFIG_NVME_TARGET_TCP /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
lsmod | grep -w nvmet_tcpPrints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian builds this as a loadable module. Every release below compiles it as a module on every flavour, so whether the code is in the running kernel depends on whether that module is loaded.
- bookworm, trixie, forky, sid, bookworm · linux-6.12m
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- Build switch
- CONFIG_NVME_TARGET_TCP
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-07-27 (3 months ago)source
- CVSS
- 9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.55%, higher than 44.7% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- drivers/nvme
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 5.10.20 | 5.10.265 | dfb902462bca |
| 5.12 | 5.15.216 | 7e558308eba1 |
| 5.12 | 6.1.178 | 96fe2513df59 |
| 5.12 | 6.6.145 | e091ff83d962 |
| 5.12 | 6.12.97 | 6f9442983a3e |
| 5.12 | 6.18.40 | 088ee46c18d9 |
| 5.12 | 7.1 | dbbd07d0a702 |
| 5.11.3 | 0 | 0 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4724-1 | 2026-08-07 | bookworm 6.12.100-1~deb12u1 | tracker |
| DLA-4723-1 | 2026-08-07 | bullseye 6.1.180-1~deb11u1 | tracker |
| DLA-4720-1 | 2026-08-05 | bookworm 6.1.180-1 | tracker |
| DSA-6405-1 | 2026-07-31 | trixie 6.12.100-1 | tracker |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:NAttack vector, network
- The vulnerable NVMe/TCP target receive worker processes attacker-controlled H2C_DATA PDUs received through a listening TCP socket, making it remotely network reachable.
- AC:LAttack complexity, low
- The attacker controls digest negotiation, PDU chunking, transfer length, and digest contents, allowing a non-final digest mismatch to be triggered deterministically while keeping other I/O outstanding.
- PR:NPrivileges required, none
- A reasonable non-TLS target deployment using allow_any_host requires no credentials or local capabilities; the remote peer can negotiate data digests and submit the malicious protocol sequence directly.
- UI:NUser interaction, none
- Exploitation requires only network protocol traffic and no action by a victim user.
- S:UScope, unchanged
- The vulnerable receive processing and resulting kernel compromise occur within the target host's existing kernel security authority.
- C:HConfidentiality impact, high
- The premature reference release can free queue, request, response-buffer, and percpu-ref state while asynchronous completions still access it, creating a kernel UAF capable of arbitrary memory disclosure.
- I:HIntegrity impact, high
- The kernel UAF exposes writes through reclaimed request and queue structures and is plausibly exploitable for arbitrary kernel memory modification or code execution.
- A:HAvailability impact, high
- The refcount corruption can cause a permanent workqueue teardown deadlock, while the resulting UAF can also produce an oops or kernel panic; the network trigger can be repeated.