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CVE-2026-74425
afs: handle CB.InitCallBackState3 requests without a server record
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-2026-74425 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 | 7.1.5-1 | 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 cache manager callback path now attaches the server record to an incoming call through the rxrpc peer's app data. That association is not guaranteed to exist for every callback request, and most callback handlers already tolerate that case. Make CB.InitCallBackState3 follow the same pattern by checking whether a server record was attached before using it. If the peer is not mapped to a server record, trace the request and ignore it, matching the existing behaviour for other unmatched callback requests. This keeps the callback handler consistent with the rest of the cache manager service and avoids depending on peer state that may not be available for a given request.
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
- 0.35%, higher than 26.6% 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 |
|---|---|---|
| 6.12.101 | 6.12.101 | 42e3917cdbdc |
| 6.15 | 6.18.40 | cc848a080f7a |
| 6.15 | 7.1.5 | 0bd5f2786a87 |
| 6.15 | 7.2 | f3cf725cd284 |
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
- The bug is in the AFS cache-manager callback handler reached from remote RXRPC/UDP traffic on the CM listener (port 7001). Packets are processed via rxrpc_new_incoming_call() -> afs_deliver_cm_op_id() -> afs_deliver_cb_init_call_back_state3() without any local syscall.
- AC:LAttack complexity, low
- Once AFS is loaded, an attacker can reliably trigger the NULL server path by sending a CB.InitCallBackState3 (opcode 213) from an unmapped peer; call->server is only set from rxrpc peer app data in afs_rx_new_call() and may legitimately be NULL.
- PR:NPrivileges required, none
- Exploitation requires no Linux privileges on the victim. The callback socket accepts remote RXRPC connections without local capability checks, and incoming connections with security index 0 bypass the challenge handshake, so no authenticated local user is needed.
- UI:NUser interaction, none
- No victim user action is required beyond the system already running the AFS client module with its callback socket open; the crash is caused entirely by attacker-sent network packets.
- S:UScope, unchanged
- Impact is a kernel NULL pointer dereference and resulting oops/panic within kernel context. This is a standard kernel denial-of-service and does not cross a security boundary such as VM escape or sandbox breakout.
- C:NConfidentiality impact, none
- The failure is a NULL pointer dereference in memcmp(call->request, &call->server->_uuid, ...) when call->server is NULL. This is a pure crash with no out-of-bounds read, use-after-free, or information disclosure primitive.
- I:NIntegrity impact, none
- The vulnerability does not modify kernel or user data; it dereferences a NULL server pointer during UUID comparison. There is no memory corruption, arbitrary write, or code execution primitive.
- A:HAvailability impact, high
- Dereferencing call->server when it is NULL causes a kernel fault in the AFS async RXRPC workqueue path, producing an oops or panic and denying all system availability until reboot.