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CVE-2026-89548
SUNRPC: always drain cache_cleaner before destroying a cache_detail
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-2026-89548 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-4841-1 · 2026-10-17 · text | 6.1.190-1 | Update the kernel and reboot. DLA-4841-1 shipped the fix on 2026-10-17, in 6.1.190-1. A running kernel keeps the old code until the machine restarts. |
| 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
sunrpc_destroy_cache_detail() only cancels the global cache_cleaner delayed_work when cache_list is empty. During per-netns teardown cache_list is never empty because init_net's caches remain registered, so the cancel never fires. After unlink, the caller proceeds to cache_destroy_net() which kfrees the cache_detail while cache_clean() may still hold a dangling pointer to it. The result is a use-after-free: cache_dequeue() takes cd->queue_lock on freed memory, and cache_put() dereferences cd->cache_put as a function pointer from freed slab. Drop the list_empty guard so that cancel_delayed_work_sync() always runs, ensuring any in-flight cache_clean() completes before the cache_detail is freed. Re-arm the cleaner afterwards if other caches are still registered.
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/cache.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
- 0.13%, higher than 2.0% 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 |
|---|---|---|
| 3.4 | 5.10.270 | dec787a15c96 |
| 3.4 | 5.15.221 | 5eea874a6962 |
| 3.4 | 6.1.188 | cf239de7fdcc |
| 3.4 | 6.6.157 | 6d74ecc2be12 |
| 3.4 | 6.12.109 | 9d44836f60c8 |
| 3.4 | 6.18.50 | 2e861ce2aaa4 |
| 3.4 | 7.2.4 | 3d60fdf95114 |
| 3.4 | 7.3 | f42d0fda0c67 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4841-1 | 2026-10-17 | bookworm 6.1.190-1 | tracker |
| 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
- sunrpc_destroy_cache_detail() runs from per-netns teardown (sunrpc_exit_net, nfsd_net_exit, gss_svc_shutdown_net) when a local task creates and destroys a network namespace; remote NFS/RPC traffic populates caches but never frees cache_detail.
- AC:LAttack complexity, low
- The attacker controls both sides of the race: unshare of a user+net ns queues cache_cleaner at delay 0, writes expired entries via /proc/net/rpc/*/channel (ip_map_parse even calls cache_flush()), and drops the netns so destroy kfree()s cache_detail while cache_clean() still holds it.
- PR:LPrivileges required, low
- Unprivileged users can create a user+network namespace (unshare -Urn). /proc/net/rpc cache files inherit userns-root ownership from proc_net_ns_init, so the attacker can populate and destroy those caches without init-namespace root.
- UI:NUser interaction, none
- The attacker creates the namespace, writes the cache channel, and tears the netns down from their own processes; no victim mount, file open, or other interaction is required.
- S:UScope, unchanged
- The use-after-free corrupts host kernel heap (struct cache_detail) within the same kernel security authority and is not a VM escape, IOMMU bypass, or other cross-boundary impact.
- C:HConfidentiality impact, high
- cache_clean() calls cache_dequeue() and cache_put() on a kfree'd cache_detail; per kernel UAF guidance, reclaim of that slab object yields an arbitrary kernel read primitive.
- I:HIntegrity impact, high
- cache_put() invokes cd->cache_put from the freed slab as a function pointer, and cache_dequeue() takes cd->queue_lock on freed memory, giving a control-flow hijack/write primitive.
- A:HAvailability impact, high
- Use-after-free of cache_detail (spinlock on freed queue_lock and an indirect call through freed cache_put) causes a kernel oops or panic even when not fully exploited for code execution.