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CVE-2026-72381
ksmbd: fix use-after-free of fp->owner.name in durable handle owner check
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem fs/smb. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-72381 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 | 6.12.100-1 | Update the kernel and reboot. Fixed in 6.12.100-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
Two concurrent SMB2 durable reconnects (DH2C/DHnC) on the same persistent_id race the fp->owner.name compare-read in ksmbd_vfs_compare_durable_owner() against the kfree() in ksmbd_reopen_durable_fd()'s reopen-success path. fp->owner.name is a standalone kstrdup() buffer whose lifetime is independent of the fp refcount, and the two sites share no lock: the compare reads the buffer while the reopen frees it, so the strcmp() can dereference freed memory. Commit 7ce4fc40018d ("ksmbd: fix durable reconnect double-bind race in ksmbd_reopen_durable_fd") made the fp->conn claim atomic under global_ft.lock (closing the owner.name double-free and the ksmbd_file write-UAF), but the compare-read versus reopen-free pair was left unserialized. BUG: KASAN: slab-use-after-free in strcmp+0x2c/0x80 Read of size 1 by task kworker strcmp ksmbd_vfs_compare_durable_owner smb2_check_durable_oplock smb2_open Freed by task kworker: kfree ksmbd_reopen_durable_fd smb2_open Allocated by task kworker: kstrdup session_fd_check smb2_session_logoff The buggy address belongs to the cache kmalloc-8 Serialize both sides of the race with fp->f_lock. The global durable file-table lock still protects the durable reconnect claim, but fp->owner.name is per-open state and does not need to block unrelated durable table lookups or reconnects. The teardown is left at its existing location after the reopen-success point so that an __open_id() rollback still retains owner.name for a later legitimate reconnect to verify.
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.
fs/smb/server/vfs_cache.c
- What this is
- KERNEL SMB3 SERVER (KSMBD)MAINTAINERS section matched on fs/smb/server/ · linux-cifs@vger.kernel.org · Maintained
- Kernel module
- ksmbd
Check it on the machine
grep -wE 'CONFIG_SMBFS|CONFIG_SMB_SERVER' /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 ksmbdPrints 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, sidm
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- Build switches
- CONFIG_SMBFS, CONFIG_SMB_SERVER
- Reads as
- all on means the file is compiled; any one off means it is not.
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
- 2026-08-15 (2 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
- 0.65%, higher than 50.2% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- fs/smb
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.6.142 | 6.6.145 | fb978d720527 |
| 6.12.92 | 6.12.97 | 93d4d46bf9d4 |
| 6.18.25 | 6.18.40 | 5a5ac2852cd3 |
| 7.1 | 7.1.5 | ed98719be413 |
| 7.1 | 7.2 | 38637163501f |
| 7.0.2 | 0 | 0 |
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 flaw is reached via ksmbd's in-kernel SMB2 server on TCP port 445; remote SMB2_CREATE durable-handle reconnect packets (DH2C/DHnC) traverse ksmbd_conn_handler_loop() -> smb2_check_user_session() -> smb2_open() -> parse_durable_handle_context() -> smb2_check_durable_oplock() / ksmbd_reopen_durable_fd().
- AC:LAttack complexity, low
- The attacker controls both sides of the race by opening a durable handle, issuing SMB2_LOGOFF to preserve owner.name via session_fd_check(), then sending concurrent SMB2_CREATE durable reconnect requests for the same persistent_id from multiple connections; no timing or layout outside attacker control is required.
- PR:NPrivileges required, none
- Exploitation requires only network reachability to ksmbd and valid SMB session credentials (guest or any share user) plus tree connect; no elevated host privileges, capabilities, or local access are needed beyond share-level SMB access obtainable through the protocol itself.
- UI:NUser interaction, none
- No victim user interaction is required beyond a server running ksmbd with durable handles enabled; the attacker programmatically drives the open, logoff, and concurrent reconnect SMB2 sequence over the network.
- S:UScope, unchanged
- Impact is confined to kernel heap memory corruption and privilege escalation within the same host security authority; this is not a VM escape, container boundary bypass, or IOMMU/DMA isolation break.
- C:HConfidentiality impact, high
- strcmp() in ksmbd_vfs_compare_durable_owner() dereferences a freed kmalloc-8 fp->owner.name buffer while a concurrent ksmbd_reopen_durable_fd() kfree() runs; this slab use-after-free enables arbitrary kernel memory disclosure via heap reuse.
- I:HIntegrity impact, high
- Use-after-free of the standalone owner.name kstrdup buffer provides kernel heap corruption primitives; with heap grooming the freed slab can be reallocated for arbitrary kernel memory writes and control-flow hijacking.
- A:HAvailability impact, high
- KASAN reports slab-use-after-free in strcmp on the owner.name buffer during concurrent smb2_open durable reconnects; the UAF can trigger kernel oops or panic on ksmbd worker threads and is repeatable by resending concurrent reconnect requests.