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CVE-2026-53026
NFSD: fix nfs4_file access extra count in nfsd4_add_rdaccess_to_wrdeleg
Published 2026-06-24 (4 months ago) by the Linux kernel CNA. Subsystem fs/nfsd. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-53026 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 | not affected | 6.12.113-1 | Nothing to do. trixie never shipped the vulnerable code. |
| Debian 14forky | fixed | 7.0.10-1 | Update the kernel and reboot. Fixed in 7.0.10-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.10-1 | Update the kernel and reboot. Fixed in 7.0.10-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
In nfsd4_add_rdaccess_to_wrdeleg, if fp->fi_fds[O_RDONLY] is already set by another thread, __nfs4_file_get_access should not be called to increment the nfs4_file access count since that was already done by the thread that added READ access to the file. The extra fi_access count in nfs4_file can prevent the corresponding nfsd_file from being freed. When stopping nfs-server service, these extra access counts trigger a BUG in kmem_cache_destroy() that shows nfsd_file object remaining on __kmem_cache_shutdown. This problem can be reproduced by running the Git project's test suite over NFS.
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.
fs/nfsd/nfs4state.c
- What this is
- KERNEL NFSD, SUNRPC, AND LOCKD SERVERSMAINTAINERS section matched on fs/nfsd/ · linux-nfs@vger.kernel.org · Supported
- Kernel module
- nfsd
Check it on the machine
grep -wE 'CONFIG_NFSD|CONFIG_NFSD_V4' /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 nfsdPrints 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, sidm
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- Build switches
- CONFIG_NFSD, CONFIG_NFSD_V4
- Reads as
- all on means the file is compiled; any one off means it is not.
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
- 2026-06-24 (4 months ago)source
- CVSS
- 7.5 high
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.43%, higher than 35.4% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- fs/nfsd
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.18.4 | 6.18.33 | 4584229395d0 |
| 6.19 | 7.0.10 | b81572b07344 |
| 6.19 | 7.1 | b48f44f36e66 |
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
- NFSD is a network-facing NFS server subsystem, and the vulnerable path is reached by remote NFSv4 COMPOUND/OPEN requests over RPC.
- AC:LAttack complexity, low
- A client can drive repeated or concurrent OPEN/write-delegation activity against an exported file; the relevant race/refcount condition is controllable by issuing parallel NFS requests.
- PR:NPrivileges required, none
- In a reasonable NFS deployment using AUTH_SYS/AUTH_NULL-accessible exports, a remote client can reach this path without authenticated target-system privileges.
- UI:NUser interaction, none
- No victim user action is required; the attacker only sends NFS requests to the server.
- S:UScope, unchanged
- The impact remains within the vulnerable kernel/NFSD server security authority and does not cross a VM, sandbox, or other separate security boundary.
- C:NConfidentiality impact, none
- The bug is an extra reference/access count leak, not a use-after-free, out-of-bounds access, or information disclosure primitive.
- I:NIntegrity impact, none
- The investigation found no attacker-controlled memory overwrite or data modification primitive; the corruption is limited to over-retaining an internal reference count.
- A:HAvailability impact, high
- The leaked access counts can keep nfsd_file objects pinned and trigger a kmem_cache_destroy BUG during NFSD shutdown; repeated triggering can deny service through persistent kernel resource leakage.