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CVE-2026-89536
SUNRPC: wait for in-flight client TLS handshake callback
Published 2026-09-11 (37 days ago) by the Linux kernel CNA. Subsystem net/sunrpc. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-89536 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 | 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
xs_tls_handshake_sync() gives xs_tls_handshake_done() a reference to the lower transport before submitting the handshake request. On timeout or signal, the synchronous waiter drops that reference after calling tls_handshake_cancel(). handshake_req_cancel() returns false when handshake_complete() has already marked the request complete. In that case the completion callback can still be running, so dropping the callback-owned reference in the waiter can free the lower transport before xs_tls_handshake_done() stores xprt_err or drops its own reference. If cancellation loses to completion, wait until xs_tls_handshake_done() signals handshake_done and let the callback release its reference. This mirrors the server-side handshake lifetime handling and keeps the timeout or signal return value 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
- 2026-09-11 (37 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
- 0.64%, higher than 49.4% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- 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 |
|---|---|---|
| 6.5 | 6.6.157 | fb43997407bc |
| 6.5 | 6.12.109 | 15431820f448 |
| 6.5 | 6.18.50 | 1de391e8b94e |
| 6.5 | 7.2.4 | 7fbb6d2ab039 |
| 6.5 | 7.3 | a89dd5974588 |
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
- The bug is in the SUNRPC TCP-with-TLS client handshake (xs_tls_handshake_sync), reached when a remote NFS/RPC peer completes RPC-with-TLS; a malicious server or on-path attacker with xprtsec=tls (anonymous TLS) drives handshake_complete() over the network against the client's 10s wait.
- AC:LAttack complexity, low
- The attacker times TLS completion against the fixed XS_TLS_HANDSHAKE_TO window and can force repeated reconnects so tls_handshake_cancel() losing to handshake_complete() is reliably hittable, with no memory-layout guess or other condition outside attacker control.
- PR:NPrivileges required, none
- No privileges on the victim host are required; a remote TLS peer only needs the client to initiate or re-establish an RPC-with-TLS connection, and the handshake runs after AUTH_TLS STARTTLS but before NFS credentials are verified.
- UI:NUser interaction, none
- No victim action is needed at attack time once an NFS xprtsec=tls/mtls mount exists, because idle disconnect or server-induced reconnect automatically re-enters xs_tcp_tls_setup_socket() and the handshake wait.
- S:UScope, unchanged
- The use-after-free corrupts kernel heap state in the SUNRPC client on the same host; impact stays within that kernel's security authority and does not cross a VM, IOMMU, or sandbox boundary.
- C:HConfidentiality impact, high
- When cancel loses, the waiter still xprt_put()s the callback-owned rpc_xprt reference, so sock_xprt can be freed while xs_tls_handshake_done() writes xprt_err and the connect worker still uses lower_xprt, a heap UAF enabling arbitrary disclosure.
- I:HIntegrity impact, high
- Use-after-free of rpc_xprt/sock_xprt (ops pointers, wait queues, socket state) allows heap reuse for arbitrary writes and control-flow hijacking, not merely a crash.
- A:HAvailability impact, high
- The extra put can destroy the transport while the handshake waiter and connect worker still touch it, producing a kernel oops/panic or a hang in xprt_destroy waiting on XPRT_LOCKED, denying NFS/RPC service.