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CVE-2026-64057
afs: Fix the locking used by afs_get_link()
Published 2026-07-19 (3 months ago) by the Linux kernel CNA. Subsystem fs/afs. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-64057 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 | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
The afs filesystem in the kernel doesn't do locking correctly for symbolic links. There are a number of problems: (1) It doesn't do any locking around afs_read_single() to prevent races between multiple ->get_link() calls, thereby allowing the possibility of leaks. (2) It doesn't use RCU barriering when accessing the buffer pointers during RCU pathwalk. (3) It can race with another thread updating the contents of the symlink if a third party updated it on the server. Fix this by the following means: (0) Move symlink handling into its own file as this makes it more complicated. (1) Take the validate_lock around afs_read_single() to prevent races between multiple ->get_link() calls. (2) Keep a separate copy of the symlink contents with an rcu_head. This is always going to be a lot smaller than a page, so it can be kmalloc'd and save quite a bit of memory. It also needs a refcount for non-RCU pathwalk. (3) Split the symlink read and write-to-cache routines in afs from those for directories. (4) Discard the I/O buffer as soon as the write-to-cache completes as this is a full page (plus a folio_queue). (5) If there's no cache, discard the I/O buffer immediately after reading and copying if there is no cache.
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/afs/Makefile
fs/afs/dir.c
fs/afs/fsclient.c
fs/afs/inode.c
fs/afs/internal.h
fs/afs/symlink.c
fs/afs/validation.c
fs/afs/yfsclient.c
- What this is
- AFS FILESYSTEMMAINTAINERS section matched on fs/afs/ · linux-afs@lists.infradead.org · Supported
- Kernel module
- kafs
Check it on the machine
grep -w CONFIG_AFS_FS /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 kafsPrints 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, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed.
- bookworm, trixie, forky, sidMnot built on amd64/cloud-amd64, arm64/cloud-arm64
- M
- a module where it is built at all; some flavours do not build it
- Build switch
- CONFIG_AFS_FS
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
- 2026-07-19 (3 months 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 2.6% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- fs/afs
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.14 | 6.18.57 | 93531bca4670 |
| 6.14 | 7.0.11 | 77ea917cbed6 |
| 6.14 | 7.1 | c0410adf3da6 |
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 flaw is in the AFS client VFS `->get_link` handler reached only via local syscalls (path resolution, `readlink`, and AFS automount), not from in-kernel network protocol handlers processing remote packets.
- AC:LAttack complexity, low
- An attacker can reliably trigger the races by spawning concurrent `open`/`readlink`/pathwalk threads against the same AFS symlink, and can also drive server-side invalidation if they have AFS write access to that symlink.
- PR:LPrivileges required, low
- Exploitation requires only normal filesystem access to traverse or read AFS symlinks on an already-mounted volume; it does not require real init-namespace root, only the same permissions any unprivileged AFS user would have.
- UI:NUser interaction, none
- No victim interaction is required beyond the attacker issuing their own concurrent symlink-access syscalls on paths they can already reach.
- S:UScope, unchanged
- Impact is confined to kernel memory corruption or disclosure on the AFS client host; it does not cross VM, container, or IOMMU security boundaries.
- C:HConfidentiality impact, high
- Missing RCU protection and absent locking around symlink buffer access allow concurrent invalidation/reallocation to expose stale or freed folio memory during RCU pathwalk and concurrent `afs_read_single()` calls.
- I:HIntegrity impact, high
- The unsynchronized buffer races constitute use-after-free class corruption that can be leveraged for heap manipulation and arbitrary kernel writes, not merely a bounded symlink read error.
- A:HAvailability impact, high
- Use-after-free and concurrent invalidation of symlink folio buffers during active `get_link`/`readlink` operations can cause kernel oopses or panics, and the races are repeatable on demand.