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CVE-2026-68343
smb: client: validate DFS referral PathConsumed
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-2026-68343 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-4777-1 · 2026-09-08 · text | 6.1.187-1 | Update the kernel and reboot. DLA-4777-1 shipped the fix on 2026-09-08, in 6.1.187-1. 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
parse_dfs_referrals() validates that the response contains the fixed referral entry array and, on for-next, the per-referral string offsets. However, the response also contains a PathConsumed value that is later used for DFS path parsing. If a malformed response provides a PathConsumed value larger than the search name, later DFS parsing can advance beyond the end of the path. Validate PathConsumed against the search name length before storing it in the parsed referral.
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/client/misc.c
- What this is
- COMMON INTERNET FILE SYSTEM CLIENT (CIFS and SMB3)MAINTAINERS section matched on fs/smb/client/ · linux-cifs@vger.kernel.org · Supported
- Kernel module
- cifs
Check it on the machine
grep -wE 'CONFIG_CIFS|CONFIG_SMBFS' /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 cifsPrints 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_CIFS, CONFIG_SMBFS
- 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:H/I:N/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.51%, higher than 42.4% 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 |
|---|---|---|
| 4.11 | 6.1.183 | bfebe5110fd1 |
| 4.11 | 6.6.148 | 5b439f39f33e |
| 4.11 | 6.12.101 | 285bd4a5f3f1 |
| 4.11 | 6.18.42 | 2fdd6d196c65 |
| 4.11 | 7.1.6 | 9f88a99ed511 |
| 4.11 | 7.2 | f6f5ee2aa33b |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4777-1 | 2026-09-08 | bookworm 6.1.187-1 | 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 tainted PathConsumed value comes directly from a GET_DFS_REFERRAL response received over TCP/445 from the SMB server, so a malicious or MITM-positioned server on the network fully controls the input to the vulnerable code.
- AC:LAttack complexity, low
- The server simply sets an oversized PathConsumed (up to 65535, and it can also clear the SMB1 UNICODE flag to select the completely unvalidated branch); the resulting out-of-bounds walk past the path buffer is deterministic and needs no race or memory-layout luck.
- PR:NPrivileges required, none
- The attacker is the remote server (or a MITM on an unsigned connection) and needs no account or privilege on the victim client; the client parses the referral response as part of establishing the connection.
- UI:NUser interaction, none
- DFS referral walks are performed automatically by autofs/systemd automounts, fstab mounts at boot and reconnect-driven remounts, so a forged referral can be delivered without any user action.
- S:UScope, unchanged
- The out-of-bounds access stays within the kernel's own memory and mount context on the client; no VM, IOMMU or sandbox boundary is crossed.
- C:HConfidentiality impact, high
- prepath = full_path + path_consumed points past the end of the heap path string, and cifs_build_devname() strlen()s and copies from there, splicing adjacent kernel heap contents (up to ~64KB away) into the constructed UNC/prefixpath that is then observable via the mount source and /proc/mounts.
- I:NIntegrity impact, none
- The defect is purely an out-of-bounds read; all subsequent allocations and copies are sized from the same over-read string, so no kernel memory is written or corrupted.
- A:HAvailability impact, high
- With PathConsumed up to 65535 the pointer can run far past a small slab object into an unmapped or guarded page, so strlen() on it oopses the mounting task (and panics on panic_on_oops systems).