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CVE-2026-53398
NFSD: Fix SECINFO_NO_NAME decode error cleanup
Published 2026-07-19 (3 months ago) by the Linux kernel CNA. Subsystem fs/nfsd. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-53398 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 | fixed | 6.1.177-1 | Update the kernel and reboot. Fixed in 6.1.177-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.95-1 | Update the kernel and reboot. Fixed in 6.12.95-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.3-1 | Update the kernel and reboot. Fixed in 7.1.3-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.3-1 | Update the kernel and reboot. Fixed in 7.1.3-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
nfsd4_decode_secinfo_no_name() currently initializes sin_exp after decoding sin_style. If the XDR stream is truncated, the decoder returns nfserr_bad_xdr before sin_exp is initialized. Since commit 3fdc54646234 ("NFSD: Reduce amount of struct nfsd4_compoundargs that needs clearing"), the inline iops array is not cleared between RPC calls. A failed SECINFO_NO_NAME decode can therefore leave sin_exp holding stale union contents from a previous operation. The error response path still invokes nfsd4_secinfo_no_name_release(), which calls exp_put() on a non-NULL sin_exp. Initialize sin_exp before the first failable decode step, matching nfsd4_decode_secinfo().
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/nfs4xdr.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
- 2026-07-19 (3 months 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
- 0.54%, higher than 44.4% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- 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 |
|---|---|---|
| 5.10.220 | 5.10.260 | 8836405abdc5 |
| 5.15.154 | 5.15.211 | 49de5d31dd8f |
| 6.1 | 6.1.177 | 5ec37edcb534 |
| 6.1 | 6.6.144 | 1e04be34cafa |
| 6.1 | 6.12.95 | 161d1aaeb04d |
| 6.1 | 6.18.38 | c8a24effd96d |
| 6.1 | 7.1.3 | 46eb17d45be6 |
| 6.1 | 7.2 | 9e18e83b8846 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4717-1 | 2026-08-05 | bullseye 5.10.262-1 | tracker |
| DLA-4700-1 | 2026-07-26 | bullseye 6.1.177-1~deb11u1 | 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 nfsd4_decode_secinfo_no_name() on the NFSv4 COMPOUND RPC decode path; nfsd is an in-kernel network file server reached remotely over TCP/UDP port 2049 by any client that can connect.
- AC:LAttack complexity, low
- An attacker on the same TCP connection can first send a valid SECINFO_NO_NAME compound to leave a dangling sin_exp in the reused iops[] slot, then send a truncated SECINFO_NO_NAME to trigger nfserr_bad_xdr and nfsd4_secinfo_no_name_release() without re-initializing sin_exp.
- PR:NPrivileges required, none
- Exploitation requires only network reachability to nfsd and standard NFSv4.1 session setup (EXCHANGE_ID/CREATE_SESSION/SEQUENCE); default exports accept RPC_AUTH_NULL with no local privileges, matching an unauthenticated remote attacker on a misconfigured or internet-exposed NFS server.
- UI:NUser interaction, none
- No victim user action is required; the attacker triggers the bug entirely by sending crafted NFSv4 COMPOUND RPC requests to the server.
- S:UScope, unchanged
- Impact is confined to kernel nfsd/export-cache memory mismanagement on the NFS server; it does not cross a VM, container, or IOMMU security boundary.
- C:HConfidentiality impact, high
- The stale sin_exp causes exp_put()/cache_put() on an uninitialized or already-freed svc_export pointer, corrupting export-cache refcounts and creating a use-after-free that can be leveraged for arbitrary kernel memory disclosure.
- I:HIntegrity impact, high
- Incorrect kref_put() on a dangling or garbage svc_export pointer is exploitable memory corruption that can lead to further heap manipulation and potential arbitrary kernel code execution, not merely a bounded error.
- A:HAvailability impact, high
- Calling exp_put() on an invalid pointer reliably causes kernel oops/panic or premature export-cache destruction, producing high availability impact including NFS service disruption and possible full kernel crash.