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CVE-2026-31435
netfs: Fix read abandonment during retry
Published 2026-04-22 (6 months ago) by the Linux kernel CNA. Subsystem fs/netfs. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-31435 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 | vulnerable | 6.12.113-1 | No fix published anywhere yet, neither in Debian nor upstream for the series trixie tracks. Watch the Debian tracker page for this CVE. Advisories for trixie have historically landed a median of 11 days after publication. |
| Debian 14forky | fixed | 6.19.11-1 | Update the kernel and reboot. Fixed in 6.19.11-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 6.19.11-1 | Update the kernel and reboot. Fixed in 6.19.11-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
Under certain circumstances, all the remaining subrequests from a read request will get abandoned during retry. The abandonment process expects the 'subreq' variable to be set to the place to start abandonment from, but it doesn't always have a useful value (it will be uninitialised on the first pass through the loop and it may point to a deleted subrequest on later passes). Fix the first jump to "abandon:" to set subreq to the start of the first subrequest expected to need retry (which, in this abandonment case, turned out unexpectedly to no longer have NEED_RETRY set). Also clear the subreq pointer after discarding superfluous retryable subrequests to cause an oops if we do try to access it.
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/netfs/read_retry.c
- What this is
- FILESYSTEMS [NETFS LIBRARY]MAINTAINERS section matched on fs/netfs/ · netfs@lists.linux.dev · Supported
- Kernel module
- netfs
Check it on the machine
grep -w CONFIG_NETFS_SUPPORT /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 netfsPrints 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 with an answer 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. The build rule could not be established for 1 release, so nothing is claimed about those.
- bookworm?
- trixie, forky, sidm
- ?
- not established - no Makefile entry for the affected file
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
Where a release above reads "not established", no build rule for the affected file was found in that release's kernel tree. That is a gap in this lookup, not a finding that the code is absent.
- Build switch
- CONFIG_NETFS_SUPPORT
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
- 2026-04-22 (6 months ago)source
- CVSS
- 8.8 high
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.51%, higher than 42.4% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- fs/netfs
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.12 | 6.18.21 | 3e5fd8f53b57 |
| 6.12 | 6.19.11 | 8f2f2bd128a8 |
| 6.12 | 7.0 | 7e57523490cd |
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 vulnerable netfs retry path processes read results from network filesystem peers such as SMB/CIFS, Ceph, AFS, 9P, and NFS/fscache-backed paths. A malicious or compromised remote filesystem server can drive retry/short-read behavior over the network.
- AC:LAttack complexity, low
- The trigger is retry/abandonment state during ordinary read handling, and a malicious peer can influence short reads, retryable errors, reconnects, or malformed responses. No uncontrollable race or rare memory layout condition is required to reach the vulnerable path.
- PR:NPrivileges required, none
- The attacker can be the remote filesystem peer and needs no privileges on the vulnerable client kernel. Local credentials may be needed by a victim/client to use the mount, but not by the remote attacker.
- UI:RUser interaction, required
- The client must mount/use the network filesystem and perform or have a process perform a read that reaches the affected netfs path. Opening or reading a file is victim-side interaction.
- S:UScope, unchanged
- The impact remains within the kernel/client system security authority. This is not a VM escape, IOMMU bypass, or cross-authority boundary escape.
- C:HConfidentiality impact, high
- The bug can use an uninitialized or stale freed subrequest pointer in list traversal and field access. That kernel memory corruption/use-after-free is defensibly exploitable for information disclosure.
- I:HIntegrity impact, high
- The stale subrequest case can write fields and flags through a freed object and continue list traversal from freed memory. This is kernel memory corruption with potential arbitrary write/control-flow impact.
- A:HAvailability impact, high
- Even without full exploitation, dereferencing an uninitialized or freed subrequest pointer can oops or panic the kernel. A malicious peer can repeatedly induce the read retry condition to cause denial of service.