Look up another CVE · open CVE-2026-68457 in the interactive tracker
CVE-2026-68457
ksmbd: use opener credentials for FSCTL mutations
Published 2026-08-15 (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-2026-68457 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 | fixed | 6.1.180-1 | Update the kernel and reboot. Fixed in 6.1.180-1. A running kernel keeps the old code until the machine restarts. |
| 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
SET_SPARSE, SET_ZERO_DATA and SET_COMPRESSION operate on an open SMB handle but call VFS xattr, fallocate or fileattr helpers with the current ksmbd worker credentials. Those helpers can revalidate inode permissions, ownership and LSM policy independently of the SMB handle access mask. Run each operation with the credentials captured in the target file when the handle was opened. Keep credential handling local to these single-file FSCTLs rather than applying session credentials to the complete IOCTL handler, which also contains handle-less and multi-handle operations.
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/smb2pdu.c
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
- 2026-08-15 (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
- 0.70%, higher than 52.4% 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 | 6.1.178 | a8c18434e1f0 |
| 5.15 | 6.6.145 | 1e112c47ec5d |
| 5.15 | 6.12.97 | fb1cae6302d5 |
| 5.15 | 6.18.40 | e205f3e7e8c3 |
| 5.15 | 7.1.5 | cfb2c6f71d61 |
| 5.15 | 7.2 | c6394bcaf254 |
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 in ksmbd's SMB2 IOCTL handler, reachable remotely over TCP/445 (or SMB Direct) via smb2_ioctl() processing FSCTL_SET_SPARSE, FSCTL_SET_ZERO_DATA, and FSCTL_SET_COMPRESSION after SMB2 session setup and tree connect.
- AC:LAttack complexity, low
- An attacker deterministically opens a target file handle and sends the FSCTL; smb2_ioctl() never calls ksmbd_override_fsids(), so VFS helpers always run with privileged worker credentials instead of filp->f_cred, making the bypass reliable without races or external timing.
- PR:NPrivileges required, none
- Although a valid SMB session, writable tree, and handle with FILE_WRITE_DATA or FILE_WRITE_ATTRIBUTES are required, ksmbd supports passwordless guest sessions on guest-writable shares, so exploitation does not require prior host privileges in a reasonable deployment.
- UI:NUser interaction, none
- The attacker directly issues SMB2 IOCTL requests against handles it opened; no separate victim action such as mounting a share, opening a file, or clicking a prompt is required beyond network access to ksmbd.
- S:UScope, unchanged
- The credential bypass permits unauthorized file metadata and content mutations within the same host kernel and exported filesystem security authority; it does not cross VM, container, IOMMU, or comparable isolation boundaries.
- C:NConfidentiality impact, none
- These FSCTLs only mutate sparse/compression xattrs or zero/punch file ranges via vfs_fallocate and vfs_fileattr helpers; they provide no read primitive, kernel memory disclosure, or alternate unauthorized data exfiltration path.
- I:HIntegrity impact, high
- Privileged ksmbd worker credentials bypass opener UID, group, capability, inode, and LSM revalidation in vfs_fallocate, vfs_fileattr_set, and ksmbd_vfs_set_dos_attrib_xattr, enabling unauthorized sparse/compression attribute changes and arbitrary-range zeroing or hole-punching of protected files.
- A:HAvailability impact, high
- Repeated FSCTL_SET_ZERO_DATA requests can persistently destroy or corrupt critical exported files and dependent services by zeroing or punching arbitrary ranges with root-equivalent credentials, causing sustained loss of share data and service availability until restoration.