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CVE-2026-64058
netfs: Fix netfs_read_folio() to wait on writeback
Published 2026-07-19 (3 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-2026-64058 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 | fixedDSA-6528-1 · 2026-09-29 · text | 6.12.111-1 | Update the kernel and reboot. DSA-6528-1 shipped the fix on 2026-09-29, in 6.12.111-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4817-1 · 2026-10-04 · text | 6.12.111-1~deb12u1 | Update the kernel and reboot. DLA-4817-1 shipped the fix on 2026-10-04, in 6.12.111-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
Fix netfs_read_folio() to wait for an ongoing writeback to complete so that it can trust the dirty flag and whatever is attached to folio->private (folio->private may get cleaned up by the collector before it clears the writeback flag).
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/buffered_read.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 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, sid, bookworm · linux-6.12m
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- 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
- 2026-07-19 (3 months ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.13%, higher than 2.2% 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 | 6.12.110 | 090a8aa1894b |
| 6.12 | 6.18.34 | f17b9121bb99 |
| 6.12 | 7.0.11 | b8271cccdd5e |
| 6.12 | 7.1 | ded0c6f16060 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4817-1 | 2026-10-04 | bookworm 6.12.111-1~deb12u1 | tracker |
| DSA-6528-1 | 2026-09-29 | trixie 6.12.111-1 | 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:LAttack vector, local
- The bug is in the netfs client page-cache path (`netfs_read_folio()`), reached only through local VFS operations (read/mmap/page fault) on mounted network filesystems (CIFS, Ceph, AFS, 9p, NFS+fscache), not from remote packet handling.
- AC:LAttack complexity, low
- An attacker can reliably trigger the race by concurrently performing streaming writes and reads on the same folio from threads they control, forcing writeback while reads hit the vulnerable dirty-folio path.
- PR:LPrivileges required, low
- Exploitation requires only unprivileged access to read/write files on an already-mounted netfs-backed filesystem; no CAP_SYS_ADMIN, real root, or user-namespace capability is needed.
- UI:NUser interaction, none
- No victim interaction is required beyond the attacker (or any local process with file access) issuing the concurrent read/write operations that trigger the race.
- S:UScope, unchanged
- The vulnerability corrupts kernel heap memory during local filesystem I/O in the same kernel security domain; it does not inherently cross VM, container, or IOMMU boundaries.
- C:HConfidentiality impact, high
- The race frees `struct netfs_folio` in `folio->private` before writeback completes, creating a use-after-free that can expose or leak kernel heap contents when `netfs_read_gaps()` dereferences stale metadata.
- I:HIntegrity impact, high
- UAF on the kmalloc'd `netfs_folio` object can be leveraged for heap manipulation; corrupted `dirty_offset`/`dirty_len` values drive subsequent I/O vector setup and pagecache writes in `netfs_read_gaps()`.
- A:HAvailability impact, high
- Winning the race causes kernel oops/panic via NULL dereference or use-after-free during `netfs_read_gaps()`, and a malicious local user can repeat the trigger to deny availability on shared servers with CIFS/NFS/Ceph mounts.