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CVE-2026-74363
bpf: fix UAF by restoring RCU-delayed inode freeing in bpffs
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem kernel/bpf. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-74363 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 | 6.1.180-1 | Update the kernel and reboot. Fixed in 6.1.180-1. A running kernel keeps the old code until the machine restarts. |
| 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
commit 4f375ade6aa9 ("bpf: Avoid RCU context warning when unpinning htab with internal structs") moved inode cleanup from ->free_inode() into ->destroy_inode() to avoid sleeping in RCU context when calling bpf_any_put(). However this removed the RCU delay on freeing the inode itself and the cached symlink body (i_link), both of which can be accessed by RCU pathwalk (pick_link, may_lookup etc.). This causes a use-after-free when a concurrent unlinkat() drops the last inode reference and destroy_inode() frees the inode immediately, while another task is still walking the path in RCU mode and reads inode->i_opflags (offset +2) inside current_time() -> is_mgtime(). KASAN reports: BUG: KASAN: slab-use-after-free in is_mgtime include/linux/fs.h:2313 Read of size 2 at addr ffff8880407e4282 (offset +2 = i_opflags) The rules (per Al Viro): ->destroy_inode() called immediately, can sleep, use for blocking cleanup e.g. bpf_any_put() ->free_inode() called after RCU grace period, use for freeing inode and anything RCU-accessible e.g. i_link Fix: split the two concerns properly: - keep bpf_any_put() in bpf_destroy_inode() since it is blocking and needs to run promptly - introduce bpf_free_inode() to handle kfree(i_link) and free_inode_nonrcu() with proper RCU delay, preventing the UAF
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.
kernel/bpf/inode.c
- What this is
- BPF [GENERAL] (Safe Dynamic Programs and Tools)MAINTAINERS section matched on kernel/bpf/ · bpf@vger.kernel.org · Supported
Check it on the machine
grep -wE 'CONFIG_BPF|CONFIG_BPF_SYSCALL' /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 below compiles the affected file into the kernels it ships.
- bookworm, trixie, forky, sidy
- y
- built into the kernel image on every flavour - only a patch removes it
- Build switches
- CONFIG_BPF, CONFIG_BPF_SYSCALL
- 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
- 2026-08-15 (2 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 2.0% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- kernel/bpf
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 5.15.195 | 5.15.212 | ea1c243c39e3 |
| 6.1.157 | 6.1.178 | 5fecb71c10c2 |
| 6.6.113 | 6.6.145 | c70d0f9114c3 |
| 6.12.54 | 6.12.97 | 53649846e043 |
| 6.18 | 6.18.40 | 61f197297282 |
| 6.18 | 7.1.5 | 0497ff765746 |
| 6.18 | 7.2 | b93c55b4932d |
| 6.17.4 | 0 | 0 |
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 triggered through local VFS and bpf(2) syscalls on bpffs (unlinkat/symlinkat/openat/stat and BPF_OBJ_GET/BPF_OBJ_PIN) racing RCU pathwalk; BPF/bpffs is not reachable from remote network services.
- AC:LAttack complexity, low
- Exploitation requires a race between unlinkat dropping the last bpffs inode reference and concurrent RCU pathwalk, but the attacker controls both sides with parallel threads/syscalls and syzbot reliably reproduces the UAF without external timing.
- PR:LPrivileges required, low
- Any local user with write access to a bpffs mount (default sticky world-writable /sys/fs/bpf) can create symlinks or pin/unpin BPF objects without init-namespace root, including via unprivileged BPF or delegated bpffs mounts in user namespaces.
- UI:NUser interaction, none
- No victim action is required; the attacker programmatically races their own unlink/pathwalk operations on bpffs objects they can create and remove.
- S:UScope, unchanged
- This is a kernel heap use-after-free in bpffs inode lifetime management, enabling local privilege escalation within the same security domain rather than crossing VM, IOMMU, or sandbox boundaries.
- C:HConfidentiality impact, high
- KASAN confirmed slab use-after-free reading freed inode->i_opflags during RCU pathwalk; UAF of struct inode enables subsequent arbitrary kernel memory disclosure via heap reuse.
- I:HIntegrity impact, high
- Premature inode freeing permits attacker-controlled heap reuse and spraying, providing a standard kernel UAF path to arbitrary write and potential code execution beyond the initial 2-byte read.
- A:HAvailability impact, high
- Concurrent RCU pathwalk of a prematurely freed bpffs inode triggers KASAN slab-UAF and kernel oops; repeated triggering can panic the system or cause denial of service.