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CVE-2026-68098
ksmbd: bound DACL dedup walk to copied ACEs
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-2026-68098 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 | 6.12.101-1 | Update the kernel and reboot. Fixed in 6.12.101-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.6-1 | Update the kernel and reboot. Fixed in 7.1.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.6-1 | Update the kernel and reboot. Fixed in 7.1.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4745-1 · 2026-08-18 · text | 6.12.101-1~deb12u1 | Update the kernel and reboot. DLA-4745-1 shipped the fix on 2026-08-18, in 6.12.101-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
set_ntacl_dacl() can stop copying ACEs before consuming the full input DACL when size accounting overflows. When that happens, num_aces reflects only the ACEs that were actually copied into the output DACL, but set_posix_acl_entries_dacl() still receives nt_num_aces and uses it to walk the existing ACE array during dedup. That makes the dedup walk scan past the copied ACE array and inspect buffer tail that does not contain valid ACEs. Split the two meanings currently carried by the NT ACE count. Pass the number of copied NT ACEs to bound the dedup walk, and preserve the original "input DACL had NT ACEs" state separately for the Everyone/default ACL fallback. This keeps the dedup walk aligned with the ACEs that are actually present in the rebuilt DACL.
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/smbacl.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, sid, bookworm · linux-6.12m
- 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
- 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
- 0.41%, higher than 34.3% 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 | 6.6.148 | 6d9d7aa4a2c9 |
| 5.15 | 6.12.101 | b057a851129c |
| 5.15 | 6.18.42 | f1eba60db813 |
| 5.15 | 7.1.6 | a0ebdaa79e10 |
| 5.15 | 7.2 | 58d97fcd0bf1 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4745-1 | 2026-08-18 | bookworm 6.12.101-1~deb12u1 | tracker |
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 in-kernel SMB server (fs/smb/server/smbacl.c), triggered when a remote client sends SMB2 QUERY_INFO (security descriptor) over TCP/445; build_sec_desc() reads the attacker's stored NTACL xattr and calls set_ntacl_dacl().
- AC:LAttack complexity, low
- An authenticated attacker fully controls the crafted DACL planted via SMB2 SET_INFO and can deterministically trigger partial ACE copy (size overflow) then QUERY_INFO; no race or victim-dependent state is required beyond a file with POSIX ACLs on an ACL-xattr-enabled share.
- PR:LPrivileges required, low
- Exploitation requires a completed SMB2 session and tree connect; planting the malicious security.NTACL xattr needs FILE_WRITE_DAC via SMB2 SET_INFO, and triggering needs an open file handle for QUERY_INFO—standard low-privileged share access, not host root.
- UI:NUser interaction, none
- The server processes the attacker's SMB2 SET_INFO and QUERY_INFO requests automatically in ksmbd worker threads; no separate local user or administrator action is required beyond normal server operation.
- S:UScope, unchanged
- Impact is confined to kernel heap memory corruption and ACL processing within the ksmbd server context; it does not cross VM, container, or IOMMU security boundaries.
- C:HConfidentiality impact, high
- The dedup walk scans past copied ACEs into buffer tail without valid ACE structures, performing out-of-bounds reads including ntace->sid.sub_auth[ntace->sid.num_subauth-1] on attacker-influenced data; per kernel guidance OOB reads score High.
- I:HIntegrity impact, high
- Out-of-bounds kernel heap access during the unbounded ACE walk is a memory corruption primitive; incorrect dedup can also append extra ACEs to the rebuilt security descriptor, enabling integrity impact beyond a simple crash.
- A:HAvailability impact, high
- Walking invalid ACE headers (e.g., zero size fields) can hang the dedup loop, and out-of-bounds reads of invalid sid fields can kernel oops/panic, denying SMB service on the affected host.