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CVE-2026-89545
sunrpc: defer rq_argp and rq_resp free until after RCU grace period
Published 2026-09-11 (37 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-2026-89545 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
svc_rqst_free() frees rqstp->rq_argp and rqstp->rq_resp synchronously via kfree(), but defers the rqstp struct free via kfree_rcu(). After svc_exit_thread() calls list_del_rcu() and svc_rqst_free(), there is a window where RCU readers that started before list_del_rcu() can still traverse the thread list and find the rqstp. These readers (e.g. nfsd_nl_rpc_status_get_dumpit()) dereference rqstp->rq_argp, which has already been freed — a use-after-free. Fix this by moving the kfree of rq_argp and rq_resp into an explicit call_rcu() callback alongside the struct free. Resources not accessed by RCU readers (bvec, buffer pages, scratch folio, auth_data) remain synchronously freed.
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/svc.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
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.16%, higher than 5.2% 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 |
|---|---|---|
| 3.19 | 6.12.111 | 0ea49d69aa80 |
| 3.19 | 6.18.50 | 08bc49e05412 |
| 3.19 | 7.2.4 | e0c5693d3f9a |
| 3.19 | 7.3 | c479bde671cb |
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:LAttack vector, local
- The use-after-free is reached by NFSD_CMD_RPC_STATUS_GET, a generic-netlink dump over AF_NETLINK that walks svc_rqst threads and reads rq_argp; remote NFS RPCs never enter nfsd_nl_rpc_status_get_dumpit().
- AC:LAttack complexity, low
- The attacker fully controls the dumpit reader and can loop it while nfsd threads exit (dynamic idle-timeout kills or thread-count changes), and can further churn threads with NFS traffic; this is an attacker-driven RCU race, not a condition beyond their control.
- PR:LPrivileges required, low
- NFSD_CMD_RPC_STATUS_GET is registered with GENL_CMD_CAP_DUMP and no GENL_ADMIN_PERM, so any unprivileged process in the nfsd network namespace can invoke the dump; exploiting it does not require CAP_NET_ADMIN or root.
- UI:NUser interaction, none
- The attacker issues the netlink dump themselves; no separate victim action such as mounting a filesystem or opening a device is required.
- S:UScope, unchanged
- This is a kernel-heap use-after-free in sunrpc/nfsd on the local host; impact stays inside the kernel's security authority and does not cross a VM, IOMMU, or other security boundary.
- C:HConfidentiality impact, high
- dumpit dereferences the kfree'd rq_argp (nfsd4_compoundargs) and reads opcnt/opnums under rcu_read_lock; a kernel UAF with heap reuse of that object yields an arbitrary read primitive.
- I:HIntegrity impact, high
- The same slab UAF is heap-sprayable so a replaced rq_argp can make dumpit walk attacker-controlled args->ops[], enabling kernel memory corruption and control-flow hijacking.
- A:HAvailability impact, high
- Use-after-free of rq_argp while an RCU reader still holds the svc_rqst from sp_all_threads can oops or panic the kernel even if the UAF is not fully turned into code execution.