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CVE-2026-68083
ksmbd: fix path resolution in ksmbd_vfs_kern_path_create
Published 2026-08-10 (2 months ago) by the Linux kernel CNA. Subsystem fs/smb. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-68083 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 | vulnerable | 6.1.190-1 | No fix published anywhere yet, neither in Debian nor upstream for the series bookworm tracks. Watch the Debian tracker page for this CVE. Advisories for bookworm have historically landed a median of 23 days after publication. |
| 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
The SMB2 open lookup is rooted at the share with LOOKUP_BENEATH, but the create/mkdir/hardlink sink is not: ksmbd_vfs_kern_path_create() builds an absolute path with convert_to_unix_name() and resolves it from AT_FDCWD via start_creating_path(), so a ".." component is walked from the real filesystem root and escapes the export. An authenticated client races a missing path component so the rooted open lookup returns -ENOENT (taking the create branch) while the same component is present (a directory) when the create walk runs; the create then resolves ".." out of the share. Root the create walk at the share like the lookup and rename paths already are: resolve the parent with vfs_path_parent_lookup(..., LOOKUP_BENEATH, &share_conf->vfs_path) and create the final component with start_creating_noperm(). convert_to_unix_name() then has no callers and is removed.
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/misc.c
fs/smb/server/misc.h
fs/smb/server/vfs.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
- 2026-08-10 (2 months ago)source
- CVSS
- 9.1 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/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
- not yet assignedsource
- 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 |
|---|---|---|
| 5.15 | 6.12.97 | 489d1ded0142 |
| 5.15 | 6.18.40 | c7c884a1305a |
| 5.15 | 7.1.5 | 98185b3025be |
| 5.15 | 7.2 | 1c8951963d8e |
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
- ksmbd is the in-kernel SMB server on TCP/445; the flaw is reached from remote SMB2_CREATE (and SMB2_SET_INFO hardlink) requests processed in ksmbd_conn_handler_loop() through smb2_open()/smb2_create_link() into ksmbd_vfs_kern_path_create().
- AC:LAttack complexity, low
- Exploitation requires a TOCTOU race, but the attacker controls both sides by issuing concurrent SMB2_CREATE and directory-creation requests over one or more connections, so success does not depend on conditions outside attacker influence.
- PR:NPrivileges required, none
- SMB2_CREATE requires a valid session, tree connect, and writable share, but ksmbd supports guest/anonymous sessions on writable exports; per kernel CNA precedent, export write access alone is not elevated privilege.
- UI:NUser interaction, none
- No victim interaction is required; the attacker sends crafted SMB2 protocol requests directly to a reachable ksmbd service without needing another user to mount shares or open files.
- S:UScope, unchanged
- Impact is confined to the host kernel filesystem namespace managed by ksmbd; escaping an SMB export is not a VM, IOMMU, or separate security-authority boundary crossing.
- C:NConfidentiality impact, none
- This is a path-resolution logic flaw with no memory corruption, out-of-bounds access, or demonstrated arbitrary read of host files outside the export; impact is unauthorized creation/linking, not information disclosure.
- I:HIntegrity impact, high
- ksmbd_vfs_kern_path_create() resolves attacker paths from AT_FDCWD without LOOKUP_BENEATH, letting authenticated clients create files, directories, or hardlinks outside the exported share using the server's filesystem credentials.
- A:HAvailability impact, high
- Repeated successful escaped creates/mkdirs outside the export can exhaust root-filesystem inodes or storage (especially tmpfs/world-writable targets), causing system-wide service unavailability on affected NAS/cloud hosts.