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CVE-2026-64036
cgroup/rstat: validate cpu before css_rstat_cpu() access
Published 2026-07-19 (3 months ago) by the Linux kernel CNA. Subsystem block. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-64036 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 | 7.0.12-1 | 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. |
The vulnerability
What the bug is
css_rstat_updated() is exposed as a BPF kfunc and accepts a caller-provided cpu argument. The function uses cpu for per-cpu rstat lookups without checking whether it refers to a valid possible CPU. A BPF iter/cgroup program with CAP_BPF and CAP_PERFMON can pass an invalid cpu value. On an unfixed UBSCAN_BOUNDS test kernel, cpu == 0x7fffffff triggers: UBSAN: array-index-out-of-bounds in kernel/cgroup/rstat.c:31:9 index 2147483647 is out of range for type 'long unsigned int [64]' Call Trace: css_rstat_updated bpf_iter_run_prog cgroup_iter_seq_show bpf_seq_read Add cpu validation to the BPF-facing css_rstat_updated() kfunc and move the common implementation to __css_rstat_updated() for in-kernel callers.
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.
block/blk-cgroup.c
include/linux/cgroup.h
kernel/cgroup/rstat.c
mm/memcontrol.c
- What this is
- CONTROL GROUP - BLOCK IO CONTROLLER (BLKIO)MAINTAINERS section matched on block/blk-cgroup.c · cgroups@vger.kernel.org
Check it on the machine
grep -w CONFIG_BLK_CGROUP /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 switch
- CONFIG_BLK_CGROUP
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 2.1% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- block
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.1 | 6.18.34 | 6a01413a4e8f |
| 6.1 | 7.0.11 | fd2bd9fa7700 |
| 6.1 | 7.1 | 8817005efbdf |
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 loading and running a BPF cgroup iterator/tracing program via local syscalls (bpf, read on iter fd); the call chain is css_rstat_updated → bpf_iter_run_prog → cgroup_iter_seq_show → bpf_seq_read, with no network-facing entry point.
- AC:LAttack complexity, low
- The attacker fully controls the cpu argument passed from BPF (e.g. 0x7fffffff) and can trigger the bug deterministically on each iter read without races or victim-specific state.
- PR:LPrivileges required, low
- Exploitation requires CAP_BPF and CAP_PERFMON to load and run BPF_PROG_TYPE_TRACING/cgroup-iter programs that can invoke the css_rstat_updated kfunc, as stated in the fix commit; these are elevated but not full init-namespace root privileges.
- UI:NUser interaction, none
- No victim interaction is required; the attacker triggers the bug by loading their own BPF program and reading from the attached iterator file descriptor.
- S:UScope, unchanged
- The vulnerability corrupts kernel memory from within kernel BPF context on the same host; it does not cross a VM/hypervisor or IOMMU security boundary.
- C:HConfidentiality impact, high
- An invalid cpu indexes __per_cpu_offset[] out of bounds and yields a wild pointer used for structure reads (llist_on_list), enabling kernel memory disclosure beyond a bounded leak.
- I:HIntegrity impact, high
- The same out-of-bounds pointer is written via try_cmpxchg on llist_node.next and llist_add into a per-CPU list head, giving exploitable out-of-bounds kernel memory corruption.
- A:HAvailability impact, high
- Operating on attacker-chosen out-of-bounds kernel addresses can cause kernel oops, panic, or hang during the corrupting cmpxchg/list operations.