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CVE-2026-74338
bpf: Reject sleepable BPF_LSM_CGROUP programs at load time
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-2026-74338 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 | vulnerable | 6.1.190-1 | No fix published anywhere yet, neither in Debian nor upstream for the series bookworm tracks. Watch the Debian tracker page for this CVE. Advisories for bookworm have historically landed a median of 23 days after publication. |
| 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 | 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
The cgroup shim runs under rcu_read_lock_dont_migrate(), so we should not attach any sleepable BPF programs there. Add support to the verifier to explicitly reject attempts to load sleepable BPF programs destined for LSM cgroup attachment. Without this, we get the following splat from a BPF_LSM_CGROUP program marked BPF_F_SLEEPABLE attached to file_open when it calls bpf_get_dentry_xattr(): BUG: sleeping function called from invalid context at kernel/locking/rwsem.c:1567 in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid: 34317, name: load preempt_count: 0, expected: 0 RCU nest depth: 2, expected: 0 Call Trace: down_read+0x76/0x480 ext4_xattr_get+0x11f/0x700 __vfs_getxattr+0xf0/0x150 bpf_get_dentry_xattr+0xbb/0xf0 bpf_prog_e76a298dac9218c6_test_open+0x6a/0x85 __cgroup_bpf_run_lsm_current+0x326/0x840 bpf_trampoline_6442534646+0x62/0x14d security_file_open+0x34/0x60 do_dentry_open+0x340/0x1260 vfs_open+0x7a/0x440 path_openat+0x1bac/0x30a0 libbpf provides a .s named section variant for every sleepable program type except lsm_cgroup, reflecting that per-cgroup LSM programs are intended to only run in a non-sleepable context. The above splat was obtained by bypassing libbpf by using bpf(2) 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.
kernel/bpf/verifier.c
- What this is
- BPF [CORE]MAINTAINERS section matched on kernel/bpf/verifier.c · bpf@vger.kernel.org · Maintained
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
- 0.18%, higher than 7.4% 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 |
|---|---|---|
| 6.0 | 6.18.57 | b4059a1f57ef |
| 6.0 | 7.1.5 | be9eaf2bb5db |
| 6.0 | 7.2 | 5b038319be44 |
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
- Exploitation requires bpf(2) to load/attach a BPF_LSM_CGROUP program and a local file open to hit security_file_open; BPF/cgroup control is syscall-local, not reachable from remote network protocols.
- AC:LAttack complexity, low
- On kernels with CONFIG_BPF_LSM and CONFIG_CGROUP_BPF, an attacker with BPF privileges can deterministically load BPF_F_SLEEPABLE BPF_LSM_CGROUP on file_open and trigger it with their own open(), without races or external preconditions.
- PR:LPrivileges required, low
- Loading BPF_PROG_TYPE_LSM requires CAP_BPF and CAP_PERFMON, and attaching to a cgroup2 fd requires cgroup write access; both are obtainable by an unprivileged user via user namespaces (unshare -Urn) per kernel CVSS guidance.
- UI:NUser interaction, none
- No victim interaction is required; once the sleepable BPF_LSM_CGROUP program is attached, any file open in that cgroup automatically invokes the vulnerable non-sleepable cgroup LSM shim path.
- S:UScope, unchanged
- Impact stays within kernel security authority (kernel panic/hang or memory corruption from invalid-context sleeping); it is not a VM escape, IOMMU bypass, or cross-authority sandbox breakout.
- C:HConfidentiality impact, high
- Calling sleepable helpers like bpf_get_dentry_xattr from rcu_read_lock_dont_migrate() can sleep on inode rwsems while RCU references remain, enabling use-after-free and arbitrary kernel memory disclosure beyond the intended xattr read.
- I:HIntegrity impact, high
- Sleeping in the cgroup BPF LSM RCU-critical section can corrupt VFS/inode lifetime and lock state, plausibly yielding arbitrary kernel write or control-flow hijack primitives, not merely a contained helper failure.
- A:HAvailability impact, high
- The bug triggers "BUG: sleeping function called from invalid context" (demonstrated on file_open) and can also cause RCU stalls, deadlocks, oops, or kernel panic when production kernels actually block in down_read under RCU.