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CVE-2026-68097
ksmbd: validate ACE size against SID sub-authorities
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-2026-68097 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 | fixedDLA-4841-1 · 2026-10-17 · text | 6.1.190-1 | Update the kernel and reboot. DLA-4841-1 shipped the fix on 2026-10-17, in 6.1.190-1. A running kernel keeps the old code until the machine restarts. |
| 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() validates sid.num_subauth before copying an ACE, but does not verify that the declared ACE size contains all sub-authorities described by that field. An undersized ACE can therefore be copied and later make the POSIX ACL deduplication walk inspect data beyond the copied ACE boundary. The existing initial bound check is also too small. It only ensures that the ACE size field is accessible before set_ntacl_dacl() reads sid.num_subauth farther into the input buffer. Require enough input for the fixed SID header before accessing num_subauth, reject ACEs smaller than that header, and skip ACEs whose declared size cannot contain the complete SID. This makes the validation consistent with the other ACE walk paths.
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
- 0.45%, higher than 37.4% 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 | 6.1.189 | 5a2d9fe0e87c |
| 5.15 | 6.6.148 | b7cb5bf08554 |
| 5.15 | 6.12.101 | 62d80d7c2d94 |
| 5.15 | 6.18.42 | 337022d9dfac |
| 5.15 | 7.1.6 | 61fd3559199f |
| 5.15 | 7.2 | 5152c6d49e3f |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4841-1 | 2026-10-17 | bookworm 6.1.190-1 | tracker |
| 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 bug is in ksmbd ACL handling reached from SMB2 network commands on TCP/445; build_sec_desc() is invoked from SMB2_QUERY_INFO(SecInfo) after reading attacker-supplied NT security descriptors stored via the server.
- AC:LAttack complexity, low
- An attacker fully controls ACE size and SID sub-authority fields in SMB SET_INFO/CREATE_SD_BUFFER payloads; parse_sec_desc() stores the raw SD despite parse_dacl() skipping bad ACEs, so a subsequent QUERY_INFO reliably triggers the flawed copy and dedup walk.
- PR:LPrivileges required, low
- Exploitation requires an authenticated SMB session and FILE_WRITE_DAC or FILE_WRITE_OWNER to plant the malformed SD (or CREATE_SD_BUFFER on create), but no server administrator or host root privileges; guest/writable share access is sufficient.
- UI:NUser interaction, none
- No end-user interaction is required beyond the attacker (or any client) issuing normal SMB file security operations against ksmbd; no mount, open-in-client, or other victim action is needed.
- S:UScope, unchanged
- The vulnerability is confined to kernel ksmbd processing of SMB security descriptors and does not cross a VM, container, or IOMMU security boundary; impact remains within the kernel/host security authority.
- C:HConfidentiality impact, high
- Undersized ACEs are copied with attacker-controlled num_subauth, and set_posix_acl_entries_dacl() reads ntace->sid.sub_auth[num_subauth-1] and advances by attacker-controlled ACE size, causing out-of-bounds kernel heap reads and a comparison oracle that can disclose kernel memory.
- I:HIntegrity impact, high
- The same inconsistent ACE metadata and unbounded dedup pointer arithmetic corrupt kernel heap ACL construction during security-descriptor rebuild; per kernel guidance, this class of memory corruption is treated as potentially chainable to arbitrary kernel writes and code execution.
- A:HAvailability impact, high
- Walking ACEs with attacker-controlled size fields against a truncated copy can read beyond the allocated scratch buffer and fault the kernel (oops/panic), and the bug class is triggered on every QUERY_INFO that rebuilds DACLs from poisoned xattrs.