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CVE-2026-98115
ksmbd: safely drain sessions during logoff
Published 2026-09-25 (24 days ago) by the Linux kernel CNA. Subsystem fs/smb. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-98115 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 | vulnerable | 6.12.113-1 | No fix published anywhere yet, neither in Debian nor upstream for the series trixie tracks. Watch the Debian tracker page for this CVE. Advisories for trixie have historically landed a median of 11 days after publication. |
| Debian 14forky | fixed | 7.2.7-1 | Update the kernel and reboot. Fixed in 7.2.7-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.7-1 | Update the kernel and reboot. Fixed in 7.2.7-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
SMB3 multichannel allows requests for one session to run on multiple connections. Wait for all channels bound to a session before freeing shared session objects. A deferred byte-range lock remains counted as a running request and only wakes when its file closes. Wake blocked locks during the drain without unpublishing or modifying their file objects. Synchronous CANCEL requests must invoke their cancellation callback to wake pending operations, while CHANGE_NOTIFY completion remains specific to the asynchronous path. Serialize session teardown with channel registration and previous-session cleanup, and use atomic work-state transitions so LOGOFF, CANCEL, and connection teardown invoke cancellation callbacks only once.
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/connection.c
fs/smb/server/mgmt/user_session.c
fs/smb/server/mgmt/user_session.h
fs/smb/server/smb2pdu.c
fs/smb/server/vfs_cache.c
fs/smb/server/vfs_cache.h
- 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
- 2026-09-25 (24 days ago)source
- CVSS
- 8.8 high
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.27%, higher than 17.8% 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 |
|---|---|---|
| 6.11 | 7.2.7 | a7e6df0bb926 |
| 6.11 | 7.3 | d12168084c8c |
| 6.6.48 | 0 | 0 |
| 6.10.7 | 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 racing teardowns start from SMB2 messages that ksmbd receives over TCP/445. They are an SMB2 LOGOFF handled by smb2_session_logoff(), and a SESSION_SETUP carrying PreviousSessionId handled by destroy_previous_session(). Requests in flight on other bound channels are also affected. All of these are sent by the remote client.
- AC:LAttack complexity, low
- The attacker controls both sides of the race by opening several TCP connections to the same session. Before the fix, smb2_session_logoff() only waited for its own connection (ksmbd_conn_wait_idle). It also had no tearing_down guard against a concurrent destroy_previous_session() or a second LOGOFF, so the attacker can retry the race at will.
- PR:LPrivileges required, low
- Both LOGOFF and a PreviousSessionId reconnect need a valid authenticated session. destroy_previous_session() also checks that the user name and passkey match the previous session's user. So the attacker must be an ordinary authenticated SMB user, not an unauthenticated one.
- UI:NUser interaction, none
- The attacker's own SMB requests on their own connections drive the whole sequence. No admin or victim action is needed.
- S:UScope, unchanged
- The corruption stays within the kernel's own security authority: ksmbd session, file table and tree-connect objects. No hypervisor or IOMMU boundary is crossed.
- C:HConfidentiality impact, high
- The session's file table can be torn down while it is still in use. ksmbd_close_session_fds() and ksmbd_destroy_file_table() can run at the same time, and requests on other channels can still hold objects from the table being freed. That makes a use-after-free or double free of kernel heap objects, which a heap spray can turn into a memory read.
- I:HIntegrity impact, high
- A use-after-free or double free of ksmbd_file and session objects reached from the network lets the attacker reallocate the freed memory with their own data. That can corrupt kernel memory and potentially hijack control flow.
- A:HAvailability impact, high
- Freeing session objects during concurrent teardown can oops or panic the kernel. Deferred byte-range locks that never wake can also hang the drain. The attacker can repeat either on demand.