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CVE-2026-64259
fuse-uring: make a fuse_req on SQE commit only findable after memcpy
Published 2026-07-25 (3 months ago) by the Linux kernel CNA. Subsystem fs/fuse. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-64259 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 | not affected | 6.12.113-1 | Nothing to do. trixie never shipped the vulnerable code. |
| Debian 14forky | fixed | 7.1.4-1 | Update the kernel and reboot. Fixed in 7.1.4-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.4-1 | Update the kernel and reboot. Fixed in 7.1.4-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
Bad userspace might try to trick us and send commit SQEs request unique / commit-id of requests that are not even send to fuse-server (io_uring_cmd_done() not called) yet. fuse_uring_commit_fetch() ends the fuse request when the ring entry has a wrong state, but that could have caused a use-after-free with the memcpy operations in fuse_uring_send_in_task(). In order to avoid such races the call of fuse_uring_add_to_pq() is moved after the copy operations and just before completing the io-uring request - malicious userspace cannot find the request anymore until all prepration work in fuse-client/kernel is completed. This also moves fuse_uring_add_to_pq() a bit up in the code to avoid a forward declaration. Also not with a preparation commit, to make it easier to back port to older kernels.
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/fuse/dev_uring.c
- What this is
- FUSE FILESYSTEM [IO-URING]MAINTAINERS section matched on fs/fuse/dev_uring.c · fuse-devel@lists.linux.dev · Maintained
Check it on the machine
grep -wE 'CONFIG_FUSE_FS|CONFIG_FUSE_IO_URING' /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.
Show whether Debian builds this, per release
Debian builds this code. Every release with an answer below compiles the affected file into the kernels it ships. The build rule could not be established for 2 releases, so nothing is claimed about those.
- bookworm, trixie?
- forky, sidy
- ?
- not established - no Makefile entry for the affected file
- y
- built into the kernel image on every flavour - only a patch removes it
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 switches
- CONFIG_FUSE_FS, CONFIG_FUSE_IO_URING
- 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
- 2026-07-25 (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
- 0.16%, higher than 4.9% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- fs/fuse
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.14 | 6.18.39 | e1711479e906 |
| 6.14 | 7.1.4 | a635f427d57e |
| 6.14 | 7.2 | 1efd3d474fc0 |
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
- Triggering requires local filesystem operations and IORING_OP_URING_CMD submissions on an associated /dev/fuse descriptor. Network peers cannot directly reach this commit path.
- AC:LAttack complexity, low
- The attacker controls request generation, predictable sequential commit IDs, concurrent commit submission, and deferred io_uring task-work execution. Both sides of the race are attacker-controlled.
- PR:LPrivileges required, low
- An ordinary user can create and operate a FUSE mount through fusermount or CAP_SYS_ADMIN in a user namespace; FUSE permits user-namespace mounts and this path has no init-namespace capability check.
- UI:NUser interaction, none
- The attacker can operate both the FUSE daemon and a client thread that generates requests, requiring no victim action.
- S:UScope, unchanged
- Exploitation compromises the host kernel within the same security authority and does not cross a VM, IOMMU, or comparable boundary.
- C:HConfidentiality impact, high
- The freed request's argument pointers and copy sources are dereferenced while copying into attacker-controlled ring memory. Heap reclamation can therefore expose sensitive kernel memory.
- I:HIntegrity impact, high
- The use-after-free performs writes to reclaimed request memory through embedded spinlocks and request flags, providing exploitable heap corruption that may enable arbitrary writes or kernel code execution.
- A:HAvailability impact, high
- The dangling request can cause invalid dereferences, corrupted request state, double completion, hangs, or a kernel panic.