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CVE-2026-74436
rxrpc: serialize kernel accept preallocation with socket teardown
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem net/rxrpc. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-74436 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 | fixedDLA-4777-1 · 2026-09-08 · text | 6.1.187-1 | Update the kernel and reboot. DLA-4777-1 shipped the fix on 2026-09-08, in 6.1.187-1. A running kernel keeps the old code until the machine restarts. |
| 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
rxrpc_kernel_charge_accept() reads rx->backlog without any socket/backlog synchronization and passes that raw pointer into rxrpc_service_prealloc_one(). A concurrent rxrpc_discard_prealloc() sets rx->backlog = NULL and frees the backlog rings, so a kernel preallocation worker can keep using a freed struct rxrpc_backlog while updating *_backlog_head/tail and array slots. Serialize the state check and backlog lookup with the socket lock, and reject kernel preallocation once teardown has disabled listening or discarded the service backlog.
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.
net/rxrpc/call_accept.c
- What this is
- RXRPC SOCKETS (AF_RXRPC)MAINTAINERS section matched on net/rxrpc/ · linux-afs@lists.infradead.org · Supported
- Kernel module
- rxrpc
Check it on the machine
grep -w CONFIG_AF_RXRPC /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 rxrpcPrints 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_AF_RXRPC
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
- 0.40%, higher than 32.6% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- net/rxrpc
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 4.9 | 5.10.266 | d6207326b4ca |
| 4.9 | 5.15.217 | 11b429b84c87 |
| 4.9 | 6.1.184 | c20d983968f2 |
| 4.9 | 6.6.148 | 0337cdba0c47 |
| 4.9 | 6.12.101 | dfa0b2bbc5e5 |
| 4.9 | 6.18.40 | 35a967ff8b24 |
| 4.9 | 7.1.5 | 1741378a7a83 |
| 4.9 | 7.2 | dc175389b18c |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4777-1 | 2026-09-08 | bookworm 6.1.187-1 | tracker |
| 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:NAttack vector, network
- RxRPC is a UDP network protocol; remote peers can send packets to AFS callback-manager listeners (port 7001) that instantiate incoming calls and queue kernel preallocation work reaching rxrpc_kernel_charge_accept().
- AC:LAttack complexity, low
- The attacker controls the preallocation side by flooding concurrent rxrpc/AFS callback traffic while a peer thread tears down the same socket via listen(0), shutdown, or close during AFS netns exit, creating a winnable race.
- PR:NPrivileges required, none
- No local account, capability, or authentication is required to reach the vulnerable preallocation path; any remote host that can deliver rxrpc/UDP packets to a listening AFS callback manager can drive the charge_accept worker.
- UI:NUser interaction, none
- Exploitation requires no victim interaction beyond normal background AFS service operation; the attacker triggers the bug purely through network traffic timed against automatic or administrative socket teardown.
- S:UScope, unchanged
- The use-after-free corrupts kernel heap metadata and rxrpc backlog structures within kernel memory, enabling local privilege escalation but not crossing a VM, container, or IOMMU security boundary by itself.
- C:HConfidentiality impact, high
- Concurrent use of a freed struct rxrpc_backlog allows reads and corruption of recycled slab memory, providing a standard kmalloc UAF primitive that can leak kernel pointers and sensitive data.
- I:HIntegrity impact, high
- The race writes peer, connection, and call pointers plus head/tail indices into freed backlog ring slots, enabling heap grooming and arbitrary kernel memory corruption exploitable for code execution.
- A:HAvailability impact, high
- Use-after-free on the backlog structure during concurrent head/tail and pointer-array updates can cause kernel oops, panic, or hang, and repeated triggering enables sustained denial of service.