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CVE-2026-90235
sunrpc: xprtsock: annotate shared socket callbacks with READ_ONCE/WRITE_ONCE
Published 2026-09-17 (31 days ago) by the Linux kernel CNA. Subsystem net/sunrpc. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-90235 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 | vulnerable | 6.1.190-1 | No fix published anywhere yet, neither in Debian nor upstream for the series bookworm tracks. Watch the Debian tracker page for this CVE. Advisories for bookworm have historically landed a median of 23 days after publication. |
| Debian 13trixie | fixedDSA-6528-1 · 2026-09-29 · text | 6.12.111-1 | Update the kernel and reboot. DSA-6528-1 shipped the fix on 2026-09-29, in 6.12.111-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4817-1 · 2026-10-04 · text | 6.12.111-1~deb12u1 | Update the kernel and reboot. DLA-4817-1 shipped the fix on 2026-10-04, in 6.12.111-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
xprtsock replaces and restores sk->sk_data_ready and sk->sk_write_space on live sockets with plain stores, and xs_udp_do_set_buffer_size() invokes sk->sk_write_space via a plain load. These callback pointers are shared with generic socket and protocol paths that may read or invoke them concurrently, so xprtsock needs the same READ_ONCE()/WRITE_ONCE() callback visibility contract that the validated 4022 family applied elsewhere. When SUNRPC takes over an AF_LOCAL, UDP, or TCP socket and later restores the lower-socket callbacks during teardown, another CPU may still hold an earlier callback snapshot. The plain replace/restore pattern leaves the same visibility hole as the validated 4022 family, so a stale snapshot can still invoke xs_data_ready() or xs_udp_write_space() after the live callback fields have already been restored to the lower-socket handlers. Use WRITE_ONCE() for the shared sk_data_ready and sk_write_space stores in xs_local_finish_connecting(), xs_udp_finish_connecting(), xs_tcp_finish_connecting(), and xs_restore_old_callbacks(). Use READ_ONCE() for the direct sk_write_space invocation in xs_udp_do_set_buffer_size(). This matches the required callback visibility contract while leaving adjacent sk_state_change and sk_error_report handling unchanged.
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/sunrpc/xprtsock.c
- What this is
- KERNEL NFSD, SUNRPC, AND LOCKD SERVERSMAINTAINERS section matched on net/sunrpc/ · linux-nfs@vger.kernel.org · Supported
- Kernel module
- sunrpc
Check it on the machine
grep -w CONFIG_SUNRPC /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 sunrpcPrints 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 as a loadable module. Every release below compiles it as a module on every flavour, so whether the code is in the running kernel depends on whether that module is loaded.
- bookworm, trixie, forky, sid, bookworm · linux-6.12m
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- Build switch
- CONFIG_SUNRPC
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
- 2026-09-17 (31 days 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
- 0.62%, higher than 48.5% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- net/sunrpc
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 2.6.15 | 6.6.157 | ed80d009b154 |
| 2.6.15 | 6.12.110 | 589f761236e0 |
| 2.6.15 | 6.18.52 | da652cb17f9f |
| 2.6.15 | 7.2.6 | d8f0b8375380 |
| 2.6.15 | 7.3 | 33930840b5f0 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4817-1 | 2026-10-04 | bookworm 6.12.111-1~deb12u1 | tracker |
| DSA-6528-1 | 2026-09-29 | trixie 6.12.111-1 | 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
- NFSv4.0 SETCLIENTID/SETCLIENTID_CONFIRM (nfsd4_setclientid → gen_callback → setup_callback_client with XPRT_TRANSPORT_TCP) makes nfsd run xs_tcp_finish_connecting; the peer's callback TCP segments hit READ_ONCE(sk_data_ready) in tcp_data_queue and READ_ONCE(sk_write_space) in sock_wfree. NFS client RPC-over-TCP/UDP replies use the same xprtsock callbacks.
- AC:LAttack complexity, low
- The attacker drives both sides: SETCLIENTID_CONFIRM then a later SETCLIENTID or TCP RST forces xs_tcp_finish_connecting versus xs_restore_old_callbacks (nfsd4_process_cb_update → rpc_shutdown_client → xs_reset_transport), while concurrent callback replies and TX skb frees take sock_wfree's lockless sk_write_space snapshot. The race is retryable on new callback sockets.
- PR:NPrivileges required, none
- SETCLIENTID and SETCLIENTID_CONFIRM are ALLOWED_WITHOUT_FH. Typical nfsd deployments accept AUTH_SYS/AUTH_NULL, so a remote peer that can reach TCP/2049 needs no local account or capability on the NFS server to create and tear down the callback xprtsock.
- UI:NUser interaction, none
- The attacker sends SETCLIENTID/SETCLIENTID_CONFIRM and the callback-channel TCP segments itself. No victim mount or other interactive action is required beyond nfsd already serving NFSv4.0.
- S:UScope, unchanged
- Stale xs_data_ready or xs_udp_write_space running against a torn-down sock_xprt corrupts kernel memory on the host that owns the RPC socket. This is not a guest-to-host, IOMMU, or other cross-authority escape.
- C:HConfidentiality impact, high
- A stale xs_data_ready after xs_restore_old_callbacks can still see a non-NULL sk_user_data via xprt_from_sock and call transport->old_data_ready plus read sock_xprt fields, leaking kernel heap once that xprt is reused or freed.
- I:HIntegrity impact, high
- The same callback/user_data desync lets xs_write_space queue_work on a freed recv_worker/error_worker and decrement sk_write_pending while xs_reset_transport is in __fput_sync, giving an arbitrary kernel write and control-flow hijack.
- A:HAvailability impact, high
- Use-after-free of sock_xprt in xs_data_ready, xs_udp_write_space, or xs_tcp_write_space from sock_wfree or tcp_data_queue after xs_restore_old_callbacks oopses or panics the kernel even without a full write primitive.