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CVE-2026-72217
SUNRPC: Bound-check xdr_buf_to_bvec() stores before writing
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem net/sunrpc. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-72217 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 | fixed | 6.12.100-1 | Update the kernel and reboot. Fixed in 6.12.100-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
xdr_buf_to_bvec() writes a bio_vec into the caller's array before testing whether that slot is in range, and the head branch performs the store with no check at all. When the caller's budget is exactly used up, the next store lands one element past the end of the array. The overflow label returns count - 1, which masks the surplus store but cannot undo it. rq_bvec, the array passed by nfsd_vfs_write(), is allocated to exactly rq_maxpages entries with no slack. The OOB store can land in adjacent slab memory; the bv_len and bv_offset fields written there are derived from client-supplied RPC payload sizes. Move the in-range check ahead of the store in the head, page-loop, and tail branches. With the check at the top of each sequence, count is incremented only after a successful store, so the overflow label can return count directly.
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/xdr.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, sidm
- 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
- 2026-08-15 (2 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
- 0.64%, higher than 49.4% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- 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 |
|---|---|---|
| 6.6 | 6.6.145 | 4a1148f2739d |
| 6.6 | 6.12.97 | 6029e711a818 |
| 6.6 | 6.18.40 | 69e18135e2a0 |
| 6.6 | 7.1.5 | 98414b42530a |
| 6.6 | 7.2 | 42f5b80dda6b |
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
- Remote attackers reach xdr_buf_to_bvec() through network-facing nfsd SUNRPC on TCP/UDP port 2049 (and NFS/RDMA transports); a crafted NFS WRITE RPC supplies the xdr_buf processed by nfsd4_write()/nfsd_proc_write() into nfsd_vfs_write().
- AC:LAttack complexity, low
- The attacker controls NFS WRITE payload size and RPC record layout to exhaust the rq_bvec bio_vec budget; the one-element out-of-bounds store is a deterministic protocol craft, not a race or memory-layout condition outside attacker control.
- PR:NPrivileges required, none
- No local shell or init-namespace root is required; a remote NFS client with export write permission (typical AUTH_UNIX/AUTH_NULL mappings on misconfigured or permissive exports) can issue crafted WRITE requests after normal NFS open/stateid setup.
- UI:NUser interaction, none
- Exploitation requires only attacker-initiated NFS RPC traffic to an exposed nfsd instance; no separate victim must mount shares, open files, or perform other interactive actions beyond the attacker operating their own client.
- S:UScope, unchanged
- Impact is a kernel heap out-of-bounds write adjacent to the per-thread rq_bvec kmalloc array during nfsd request handling; this enables privilege escalation on the NFS server host but does not cross VM, container, or IOMMU security boundaries.
- C:HConfidentiality impact, high
- The overflow stores a full bio_vec (page pointer plus attacker-controlled bv_len and bv_offset derived from client RPC payload sizes) into adjacent slab memory; such heap corruption can disclose kernel memory and is not a bounded benign leak.
- I:HIntegrity impact, high
- Attacker-controlled bio_vec fields are written past the end of rq_bvec into adjacent kernel heap objects, providing a memory-corruption primitive that can be developed into arbitrary kernel writes and code execution, not merely limited data alteration.
- A:HAvailability impact, high
- The extraneous store corrupts adjacent slab memory; on vulnerable kernels the overflow path returned count-1 without aborting nfsd_vfs_write(), so servers can kernel oops, panic, or hang during or after malformed writes even before full exploitation.