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CVE-2026-63800
pNFS: Fix use-after-free in pnfs_update_layout()
Published 2026-07-19 (3 months ago) by the Linux kernel CNA. Subsystem fs/nfs. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-63800 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
When hitting the NFS_LAYOUT_RETURN branch in pnfs_update_layout(), the code calls pnfs_prepare_to_retry_layoutget(lo). If it succeeds, pnfs_put_layout_hdr(lo) is called before trace_pnfs_update_layout(), which still references 'lo'. This results in a use-after-free when the tracepoint accesses lo's fields. Fix this by moving the tracepoint call before pnfs_put_layout_hdr(lo).
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/nfs/pnfs.c
- What this is
- NFS, SUNRPC, AND LOCKD CLIENTSMAINTAINERS section matched on fs/nfs/ · linux-nfs@vger.kernel.org · Maintained
- Kernel module
- nfsv4
Check it on the machine
grep -wE 'CONFIG_NFS_FS|CONFIG_NFS_V4|CONFIG_NFS_V4_1' /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 nfsv4Prints 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_NFS_FS, CONFIG_NFS_V4, CONFIG_NFS_V4_1
- 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
- 0.53%, higher than 43.4% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- fs/nfs
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 5.10.9 | 5.10.260 | 4ad8b9a85dbf |
| 5.11 | 5.15.211 | 1f24b8302c77 |
| 5.11 | 6.1.177 | 9c0fb5c09ae5 |
| 5.11 | 6.6.144 | 7e37e9b3e82a |
| 5.11 | 6.12.95 | 2883ddd7542b |
| 5.11 | 6.18.38 | 200e7637f4d6 |
| 5.11 | 7.1.3 | 9645aaf689af |
| 5.11 | 7.2 | 13e198a90ca4 |
| 5.4.91 | 0 | 0 |
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
- A compromised or malicious pNFS NFSv4.1+ metadata server can send CB_LAYOUTRECALL callbacks over the NFSv4 backchannel to force NFS_LAYOUT_RETURN while client file I/O reaches pnfs_update_layout(), exploiting the client from the network in typical enterprise/HPC pNFS deployments.
- AC:LAttack complexity, low
- The attacker controls both sides of the race by issuing layout recalls from the server and driving or waiting for concurrent read/write I/O on the mounted pNFS share; no conditions beyond attacker influence are required once a pNFS session exists.
- PR:NPrivileges required, none
- Exploitation requires no local privileges on the victim client—a remote NFS server with an established pNFS session can trigger the layoutreturn/retry path while any client process performs permitted file I/O on the mount.
- UI:NUser interaction, none
- No interactive victim action is needed during exploitation; automated workloads, daemons, or batch jobs performing routine I/O on an existing pNFS mount are sufficient to hit the vulnerable code path.
- S:UScope, unchanged
- The use-after-free corrupts kernel heap memory within the same kernel security domain and does not cross a VM, container, or IOMMU boundary on its own.
- C:HConfidentiality impact, high
- The tracepoint reads freed pnfs_layout_hdr fields (plh_stateid seqid and hash) after pnfs_put_layout_hdr() drops the final reference, giving an attacker-controlled use-after-free read primitive over kernel heap memory.
- I:HIntegrity impact, high
- Use-after-free on a refcounted kernel layout object enables heap grooming and further memory corruption for arbitrary kernel writes or control-flow hijacking, not merely a bounded fault.
- A:HAvailability impact, high
- Dereferencing a freed pnfs_layout_hdr in kernel context can cause an oops or panic, and use-after-free corruption reliably threatens system availability even when full exploitation is not attempted.