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CVE-2026-72372
afs: Fix lack of locking around modifications of net->cells_dyn_ino
Published 2026-08-15 (2 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-2026-72372 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 | 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 | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. 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
Fix the lack of locking around modifications of net->cells_dyn_ino by taking net->cells_lock exclusively. This also requires to cell to be removed from net->cells_dyn_ino in afs_destroy_cell_work() rather than in afs_cell_destroy() as the latter runs in RCU cleanup context and sleeping locks cannot be taken there.
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/cell.c
fs/afs/dynroot.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, sid, bookworm · linux-6.12Mnot 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
- 2026-08-15 (2 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
- 0.18%, higher than 6.5% 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 |
|---|---|---|
| 6.12.97 | 6.12.101 | 4d8a2fe88478 |
| 6.15 | 6.18.40 | 2ffb70a8a019 |
| 6.15 | 7.1.5 | e94f92fd56c5 |
| 6.15 | 7.2 | 55e841836c6f |
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:LAttack vector, local
- The bug is reached only through local VFS operations on an AFS dynroot mount (getdents/readdir via afs_dynroot_readdir, lookup via afs_dynroot_lookup_cell) and cell create/destroy paths (afs_alloc_cell/afs_destroy_cell_work), not from remote AFS/RxRPC packet handling.
- AC:LAttack complexity, low
- An attacker can reliably win the race by running concurrent threads that repeatedly readdir /afs while creating and expiring cells through lookups or /proc/net/afs/cells writes; syzbot and public PoCs reproduced the slab UAF within minutes without uncontrollable layout dependencies.
- PR:LPrivileges required, low
- Exploitation requires only an unprivileged local user who can access a dynroot mount (typical world-readable /afs on AFS clients) or mount AFS with -o dyn inside a user namespace where CAP_SYS_ADMIN is available; real init-namespace root is not required.
- UI:NUser interaction, none
- No victim interaction is needed once dynroot is available; the attacker directly issues the readdir and cell-creation syscalls that race unsynchronized idr_alloc_cyclic, idr_remove, and idr_get_next on net->cells_dyn_ino.
- S:UScope, unchanged
- Impact is confined to kernel memory integrity and privilege boundaries within the host kernel; it does not cross VM, container, or IOMMU security scopes into a different authority.
- C:HConfidentiality impact, high
- Concurrent idr_remove during afs_dynroot_readdir_cells leaves idr_get_next with a dangling afs_cell pointer, causing slab use-after-free reads of cell->name and cell->state (confirmed by KASAN in afs_dynroot_readdir) and enabling further kernel memory disclosure.
- I:HIntegrity impact, high
- IDR tree corruption and use-after-free of afs_cell objects provide attacker-influenced heap corruption primitives that can be developed into arbitrary kernel writes or control-flow hijack, not merely a benign error return.
- A:HAvailability impact, high
- The race causes kernel oops/panic from corrupted IDR traversal or use-after-free during dir_emit; repeated triggering can crash or hang the system, satisfying high availability impact.