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CVE-2026-98318
smb: client: validate absolute native symlink targets before NT fixups
Published 2026-10-06 (13 days ago) by the Linux kernel CNA. Subsystem fs/smb. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-98318 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 | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | not affected | 6.12.113-1 | Nothing to do. trixie never shipped the vulnerable code. |
| Debian 14forky | fixed | 7.2.8-1 | Update the kernel and reboot. Fixed in 7.2.8-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.8-1 | Update the kernel and reboot. Fixed in 7.2.8-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
With symlinkroot unset, an absolute target is copied without conversion to an NT drive path. Later code still assumes an NT prefix is present when modifying the target and calculating the print name length. For "/ab", this causes two failures: sym[5] and path[5] are written past their allocations, and plen -= 2 * poff subtracts an assumed 8-byte prefix from a 6-byte UTF-16 target, wrapping u16 plen to 65534. That underflow causes another overflow: memcpy() copies 65534 bytes into a 24-byte buffer. A user with write access to a mounted share can trigger these bugs with default settings. Validate the NT drive prefix, including an ASCII drive letter, before accessing fixed offsets or subtracting the prefix length.
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/reparse.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 with an answer 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. The build rule could not be established for 1 release, so nothing is claimed about those.
- bookworm?
- trixie, forky, sidm
- ?
- not established - no Makefile entry for the affected file
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
Where a release above reads "not established", no build rule for the affected file was found in that release's kernel tree. That is a gap in this lookup, not a finding that the code is absent.
- 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
- 2026-10-06 (13 days ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.13%, higher than 2.3% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- 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 |
|---|---|---|
| 6.16 | 7.2.8 | 6913ff607c2b |
| 6.16 | 7.3 | 23c240d9509e |
| 6.15.6 | 0 | 0 |
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:LAttack vector, local
- The malformed input is the symlink target string a local user passes to symlink(2) on a CIFS mount (cifs_symlink -> create_reparse_symlink -> create_native_symlink); the SMB server supplies none of the bad data, and the overflow happens before any request is sent.
- AC:LAttack complexity, low
- With default options (reparse_type defaults to NFS so cifs_symlink_type() returns NATIVE, symlinkroot unset) a target like "/ab" deterministically triggers the plen underflow; detect_directory_symlink_target() returns 0 for absolute targets, so nothing on the path depends on state outside the attacker's control.
- PR:LPrivileges required, low
- The attacker needs only an ordinary local account with write access to a directory on an already-mounted CIFS share whose server advertises FILE_SUPPORTS_REPARSE_POINTS; cifs is not mountable from user namespaces, so no further privilege is gained there.
- UI:NUser interaction, none
- The attacker triggers the bug entirely through their own symlink(2) call; no victim action is needed beyond the share already being mounted.
- S:UScope, unchanged
- Heap corruption in the CIFS client stays within the local kernel's security authority; this is ordinary local privilege escalation or crash with no VM or IOMMU boundary crossed.
- C:HConfidentiality impact, high
- memcpy(buf->PathBuffer, path+poff, plen) reads 65534 bytes past the small UTF-16 path allocation, and the matching heap overflow can be groomed into read primitives over adjacent slab objects.
- I:HIntegrity impact, high
- Out-of-bounds heap writes: sym[5]/path[5] past their allocations, and a 65534-byte memcpy into a 24-byte kzalloc buffer after u16 plen and len wrap, corrupting adjacent slab objects in a way usable for control-flow hijack.
- A:HAvailability impact, high
- The 64 KiB overflow of the kmalloc buffer corrupts large amounts of slab memory and reliably oopses or panics the kernel, and any user with write access to the share can repeat it.