CVE-2024-41009: Linux Kernel Use-After-Free Vulnerability

CVE-2024-41009 Overview

CVE-2024-41009 is a Linux kernel vulnerability in the Berkeley Packet Filter (BPF) ring buffer implementation. The flaw allows a local attacker with the ability to load BPF programs to overrun ring buffer reservations and corrupt internal record headers. Exploiting the issue can cause kernel memory corruption and result in a denial of service through a kernel crash. The vulnerability is tracked under [CWE-770] (Allocation of Resources Without Limits or Throttling) and affects multiple stable Linux kernel branches. The Linux kernel maintainers resolved the issue with a fix that validates the oldest pending position against the ring buffer size before granting new reservations.

Critical Impact
A local user able to load BPF programs can corrupt BPF ring buffer metadata, leading to a kernel crash and high-availability impact on affected systems.

Affected Products

Linux Kernel (multiple stable branches prior to the patch commits)
Distributions shipping affected kernels, including Debian (per Debian LTS advisory)
Systems exposing BPF program loading to unprivileged or semi-privileged users

Discovery Timeline

2024-07-17 - CVE-2024-41009 published to NVD
2025-01 - Debian LTS security advisory issued for affected kernel packages
2025-11-03 - Last updated in NVD database

Technical Details for CVE-2024-41009

Vulnerability Analysis

The BPF ring buffer is implemented as a power-of-2 circular buffer backed by two monotonically increasing counters: consumer_pos and producer_pos. The data region is mapped twice contiguously in virtual memory so records wrapping the end of the buffer remain linearly addressable. Each record carries a struct bpf_ringbuf_hdr { u32 len; u32 pg_off; } header used by bpf_ringbuf_submit() and bpf_ringbuf_discard() to locate the owning ring buffer via bpf_ringbuf_restore_from_rec().

The reservation logic in bpf_ringbuf_reserve() validated new producer positions against consumer_pos using the check new_prod_pos - cons_pos > rb->mask. Because consumer_pos is writable from user space, an attacker can advance it before reserving, bypassing the size check and permitting two outstanding reservations whose combined span exceeds the buffer mask. The double-mapped layout then causes the second chunk to alias the first chunk's header in virtual memory.

Root Cause

The reservation path relies on a counter (consumer_pos) that is mutable from user space without cross-validating the oldest still-pending producer reservation. This permits resource over-allocation against the circular buffer's capacity, the classic pattern described by [CWE-770].

Attack Vector

An attacker creates a BPF_MAP_TYPE_RINGBUF map of size 0x4000, writes consumer_pos = 0x3000 from user space, then calls bpf_ringbuf_reserve() to allocate chunk A spanning [0x0, 0x3008]. A second reservation of size 0x3000 produces chunk B at [0x3008, 0x6010]. Due to the double mapping, bytes [0x4000, 0x4008] of chunk B alias chunk A's header. The BPF program rewrites pg_off, and the subsequent bpf_ringbuf_commit() dereferences an attacker-controlled offset to locate the ring buffer structure, crashing the kernel.

No verified public exploit code is available. Refer to the Kernel.org commit log for the upstream fix and technical detail.

Detection Methods for CVE-2024-41009

Indicators of Compromise

Unexpected kernel oops or panic referencing bpf_ringbuf_commit, bpf_ringbuf_submit, or bpf_ringbuf_restore_from_rec in stack traces
Processes invoking bpf() syscall with BPF_MAP_CREATE and BPF_MAP_TYPE_RINGBUF followed by direct writes to the consumer page
Repeated BPF program loads from non-root users on systems where kernel.unprivileged_bpf_disabled is not enforced

Detection Strategies

Audit bpf() syscall activity using auditd rules targeting -S bpf to capture program loads and map creation by UID and process.
Monitor kernel ring buffer (dmesg, journalctl -k) for BUG: or general protection fault entries originating from BPF subsystem symbols.
Correlate BPF map creation events with subsequent privilege escalation or unexpected service termination.

Monitoring Recommendations

Enable kernel lockdown or restrict BPF to CAP_BPF/CAP_SYS_ADMIN holders and log any deviations.
Forward kernel crash dumps (kdump) and oops messages to a centralized log pipeline for retroactive analysis.
Track running kernel versions across the fleet and alert on hosts running pre-patch builds in the affected stable branches.

How to Mitigate CVE-2024-41009

Immediate Actions Required

Update the Linux kernel to a version containing commits 47416c85, 511804ab, cfa1a232, or d1b9df04 from the upstream stable trees.
Apply distribution kernel updates, including the Debian LTS update referenced in the Debian LTS Announcement.
Restrict BPF program loading by setting kernel.unprivileged_bpf_disabled=1 until patched kernels are deployed.

Patch Information

The fix calculates the oldest pending_pos across outstanding reservations and rejects requests whose span from the oldest outstanding record to the newest would exceed the ring buffer size. The patch is available across multiple stable branches via the Kernel.org commit log and companion commits referenced in the NVD record. The BPF selftests ring buffer benchmark (./benchs/run_bench_ringbufs.sh) was used by upstream maintainers to validate the fix with minimal performance regression.

Workarounds

Set sysctl -w kernel.unprivileged_bpf_disabled=1 to prevent non-privileged users from loading BPF programs.
Remove CAP_BPF from service accounts and containers that do not require BPF program loading.
Use seccomp filters to block the bpf() syscall in workloads where it is not needed.

bash

# Disable unprivileged BPF until kernel is patched
sudo sysctl -w kernel.unprivileged_bpf_disabled=1
echo 'kernel.unprivileged_bpf_disabled=1' | sudo tee /etc/sysctl.d/90-bpf-hardening.conf

# Verify running kernel version against patched stable releases
uname -r