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CVE-2026-72374
afs: Fix callback service message parsers to pass through -EAGAIN
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-2026-72374 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
The AFS filesystem client uses an rxrpc server to listen for callback notifications. Each callback call type handler has a delivery function that parses the incoming request stream, and this should return -EAGAIN the last packet hasn't yet been seen, but all currently queued received data is consumed. afs_extract_data() does this, but the -EAGAIN return is switched to 0 inadvertantly Fix callback service message parsers to pass through -EAGAIN
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/cmservice.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
- 7.5 high
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.72%, higher than 52.9% 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 | 26b737b3769e |
| 4.9 | 5.15.212 | 09c67a7ded48 |
| 4.9 | 6.1.178 | 239cd337c9d0 |
| 4.9 | 6.6.145 | 5a39b145a8fb |
| 4.9 | 6.12.97 | 772850871a2e |
| 4.9 | 6.18.40 | 0acbc09d2aca |
| 4.9 | 7.1.5 | f14dd036fad3 |
| 4.9 | 7.2 | 0f36469d7ce9 |
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 traffic to the kafs cache manager on UDP/TCP port 7001 reaches afs_deliver_cb_init_call_back_state3() and afs_deliver_cb_probe_uuid() via rxrpc incoming-call handling (afs_rx_new_call → afs_deliver_cm_op_id → afs_cm_incoming_call → deliver parsers).
- AC:LAttack complexity, low
- An attacker who controls an established callback RxRPC session can reliably force -EAGAIN by fragmenting CB.InitCallBackState3 or CB.ProbeUuid DATA across multiple packets; no special memory layout, races beyond attacker pacing, or rare victim state is required.
- PR:NPrivileges required, none
- No local Linux account or capabilities on the victim are needed; exploitation is driven by a remote RxRPC peer sending fragmented cache-manager callbacks after the encrypted handshake on the callback socket (minimum RXRPC_SECURITY_ENCRYPT).
- UI:NUser interaction, none
- No victim user action (mounting AFS, opening files, or clicking anything) is required at exploit time; only an active kafs client with its per-net callback listener is needed as deployment context.
- S:UScope, unchanged
- Impact is confined to kernel/AFS cache-manager state on the victim host (NULL dereference oops, panic, or callback-protocol disruption) and does not cross VM, IOMMU, or sandbox security boundaries.
- C:NConfidentiality impact, none
- The -EAGAIN mishandling returns success before UUID unmarshalling, leaving call->request NULL; SRXAFSCB_ProbeUuid passes that pointer to memcmp(), causing a kernel fault without attacker-visible disclosure of victim data.
- I:NIntegrity impact, none
- The failure mode is premature parser completion and a NULL-pointer memcmp in SRXAFSCB_ProbeUuid (plus possible premature CM replies on InitCallBackState3); no arbitrary kernel write, heap corruption, or code-execution primitive is demonstrated.
- A:HAvailability impact, high
- Treating -EAGAIN as success queues SRXAFSCB_ProbeUuid while call->request is still NULL, and memcmp() on that pointer causes a kernel oops/panic; a remote peer can retrigger this on demand with fragmented CB.ProbeUuid callbacks.