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CVE-2026-63980
net/handshake: Use spin_lock_bh for hn_lock
Published 2026-07-19 (3 months ago) by the Linux kernel CNA. Subsystem net/handshake. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-63980 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 | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | fixed | 6.12.94-1 | Update the kernel and reboot. Fixed in 6.12.94-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
nvmet_tcp_state_change(), a socket callback that runs in BH context, can reach handshake_req_cancel() via nvmet_tcp_schedule_release_queue() and tls_handshake_cancel(). handshake_req_cancel() acquires hn->hn_lock with plain spin_lock(). If a process-context thread on the same CPU holds hn->hn_lock when a softirq invokes the cancel path, the lock attempt deadlocks. This is the only caller that invokes tls_handshake_cancel() from BH context; every other consumer calls it from process context. Deferring the cancel to process context in the NVMe target is not straightforward: nvmet_tcp_schedule_release_queue() must call tls_handshake_cancel() atomically with its state transition to DISCONNECTING. If the cancel were deferred, the handshake completion callback could fire in the window before the cancel runs, observe the unexpected state, and return without dropping its kref on the queue. Reworking that interlock is considerably more invasive than hardening the handshake lock. Convert all hn->hn_lock acquisitions from spin_lock/spin_unlock to spin_lock_bh/spin_unlock_bh so the lock is never taken with softirqs enabled.
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.
net/handshake/netlink.c
net/handshake/request.c
net/handshake/tlshd.c
- What this is
- HANDSHAKE UPCALL FOR TRANSPORT LAYER SECURITYMAINTAINERS section matched on net/handshake/ · kernel-tls-handshake@lists.linux.dev · Maintained
Check it on the machine
grep -w CONFIG_NET_HANDSHAKE /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.
Show whether Debian builds this, per release
Debian builds this code. Every release with an answer below compiles the affected file into the kernels it ships. The build rule could not be established for 1 release, so nothing is claimed about those.
- bookworm?
- trixie, forky, sidy
- ?
- not established - no Makefile entry for the affected file
- y
- built into the kernel image on every flavour - only a patch removes it
Where a release above reads "not established", no build rule for the affected file was found in that release's kernel tree. That is a gap in this lookup, not a finding that the code is absent.
- Build switch
- CONFIG_NET_HANDSHAKE
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
- 2026-07-19 (3 months ago)source
- CVSS
- 7.5 high
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.44%, higher than 36.8% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- net/handshake
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.7 | 6.12.93 | 06ab5978866f |
| 6.7 | 6.18.35 | 0866569fc36a |
| 6.7 | 7.0.12 | 91898de9501a |
| 6.7 | 7.1 | cc993e0927ec |
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 path is reachable through nvmet-tcp, an in-kernel network service that processes remote TCP connections; socket state-change callbacks run in softirq when remote peers disconnect during TLS handshake.
- AC:LAttack complexity, low
- An attacker controls both sides of the race by opening multiple concurrent TLS connections to the NVMe/TCP target and timing abrupt disconnects against in-progress handshake submissions on the same CPU.
- PR:NPrivileges required, none
- Exploitation requires only network access to an NVMe/TCP target port with TLS enabled; the TLS handshake upcall occurs before any NVMe authentication or credentials are verified.
- UI:NUser interaction, none
- No victim user action is required; the deadlock is triggered entirely by the remote attacker's connection and disconnection timing against the NVMe/TCP service.
- S:UScope, unchanged
- The deadlock affects kernel availability on the target host but does not cross a security boundary such as a VM guest-to-host escape or sandbox breakout.
- C:NConfidentiality impact, none
- This is a spinlock deadlock with no memory corruption, out-of-bounds access, or use-after-free; no information disclosure occurs.
- I:NIntegrity impact, none
- The vulnerability causes a CPU hang via lock deadlock but does not modify data or enable arbitrary writes or code execution.
- A:HAvailability impact, high
- A spinlock deadlock between process context and softirq causes CPU soft lockup on the affected processor; watchdog timeout can escalate this to a full kernel panic, denying all system availability.