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CVE-2026-74427
afs: Fix netns teardown to cancel the preallocation charger
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem fs/afs. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-74427 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 | fixed | 6.1.180-1 | Update the kernel and reboot. Fixed in 6.1.180-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.100-1 | Update the kernel and reboot. Fixed in 6.12.100-1. 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. |
The vulnerability
What the bug is
Fix the teardown of an afs network namespace to make sure it cancels the work item that keeps the preallocated rxrpc call/conn/peer queue charged before incoming calls are disabled (i.e. listen 0). Also, if net->live is false because the afs netns is being deleted, make afs_charge_preallocation() skip charging and make afs_rx_new_call() avoid requeuing the charger. (This was found by AI review).
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/rxrpc.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
- 2026-08-15 (2 months ago)source
- CVSS
- 9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.76%, higher than 54.2% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- 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 |
|---|---|---|
| 4.9 | 5.10.261 | 63ccaf1bdf8b |
| 4.9 | 5.15.212 | f5096e18b6b7 |
| 4.9 | 6.1.178 | 59e8b7652f6c |
| 4.9 | 6.6.145 | 85d5fb80fe4f |
| 4.9 | 6.12.97 | a33975ff2b6e |
| 4.9 | 6.18.40 | b83ecf80e28a |
| 4.9 | 7.1.5 | eec89c5f8e1a |
| 4.9 | 7.2 | 47694fbc9d24 |
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
- Remote RxRPC/UDP traffic to the kafs callback manager on port 7001 reaches afs_rx_new_call through rxrpc incoming-call processing and can requeue charge_preallocation_work that touches per-net AFS state during namespace teardown, matching other network-reachable netns-teardown UAF bugs.
- AC:LAttack complexity, low
- The attacker controls both sides of the race—namespace create/destroy timing via user namespaces or container lifecycle, plus concurrent RxRPC callback floods—and the follow-up fix confirms incoming I/O-thread calls can requeue the charger after listen(0); the window is wide and repeatable.
- PR:NPrivileges required, none
- afs_rx_new_call is invoked during RXRPC_CONN_SERVICE_CHALLENGING before AFS credential verification completes, so a remote peer sending valid CM-service RxRPC DATA can drive the bug; alternatively an unprivileged user obtains CAP_NET_ADMIN via user namespaces to destroy the namespace.
- UI:NUser interaction, none
- No victim interaction such as mounting AFS volumes or opening files is required; exploitation relies on attacker-driven namespace teardown and/or RxRPC packets, both kernel-level events under attacker or infrastructure control.
- S:UScope, unchanged
- The UAF corrupts kernel heap objects within the same OS security authority; impact does not cross a VM, IOMMU, or KVM/Xen boundary into a separate security domain.
- C:HConfidentiality impact, high
- charge_preallocation_work on afs_wq dereferences freed struct afs_net fields (socket, spare_incoming_call, nr_outstanding_calls) after per-net exit; UAF of slab objects enables arbitrary kernel memory disclosure via heap grooming.
- I:HIntegrity impact, high
- Continued charging and afs_alloc_call through freed afs_net writes into stale per-net counters and socket state; UAF supports heap spray and arbitrary kernel write or control-flow hijack primitives.
- A:HAvailability impact, high
- Use-after-free on afs_net and its RxRPC socket during teardown causes kernel oops or panic; even without full exploitation the race reliably crashes the host and can be retriggered on demand.