CVE-2024-56614: Linux Kernel Buffer Overflow Vulnerability

CVE-2024-56614 Overview

CVE-2024-56614 is an out-of-bounds write vulnerability [CWE-787] in the Linux kernel's AF_XDP socket (XSK) map implementation. The flaw exists in the xsk_map_delete_elem function, where an implicit type conversion between an unsigned map->max_entries and a user-controlled signed integer k bypasses the intended bounds check. A local attacker with privileges to invoke the BPF syscall can pass a negative index, triggering an out-of-bounds write via the xchg operation on m->xsk_map[k].

Critical Impact
Local privilege escalation through kernel memory corruption, leading to potential code execution in kernel context and full system compromise.

Affected Products

Linux Kernel (multiple stable branches prior to fix commits)
Linux Kernel 6.13-rc1
Debian LTS distributions shipping affected kernel versions

Discovery Timeline

2024-12-27 - CVE-2024-56614 published to NVD
2025-11-03 - Last updated in NVD database

Technical Details for CVE-2024-56614

Vulnerability Analysis

The vulnerability resides in kernel/bpf/xskmap.c within the xsk_map_delete_elem function. The function compares map->max_entries (an unsigned integer) with k (a signed integer derived from user input) using the expression if (k >= map->max_entries) return -EINVAL;. Due to C integer promotion rules, the signed k is converted to unsigned for the comparison. A negative value of k becomes a large unsigned number, which may still bypass the bounds check depending on map->max_entries. The function then uses the original signed k as an array index, producing an out-of-bounds reference into m->xsk_map[k].

The subsequent xchg(map_entry, NULL) operation writes a NULL pointer to attacker-controlled memory outside the map. The kernel splat in the report shows a page fault at xsk_map_delete_elem+0x2d/0x60, confirming attacker-controlled out-of-bounds memory access. If old_xs is non-NULL, the corrupted pointer is passed to xsk_map_sock_delete, enabling further memory corruption.

Root Cause

The root cause is improper input validation through implicit signed-to-unsigned integer conversion. The bounds check fails to reject negative values for k before the value is used as an array index. The fix replaces the comparison with explicit handling that rejects negative indices and properly validates k against map->max_entries.

Attack Vector

Exploitation requires local access and the ability to invoke the bpf() syscall with map manipulation privileges. The attacker creates or accesses an XSK map and then calls BPF_MAP_DELETE_ELEM supplying a negative key value. The kernel performs an out-of-bounds write at an offset computed from the negative index, allowing kernel memory corruption that can be chained into privilege escalation. The vulnerability affects systems where unprivileged BPF is permitted or where the attacker already holds CAP_BPF or equivalent capabilities.

The vulnerability mechanism is described in prose because no verified public exploit code is available. Technical details are documented in the upstream kernel commits referenced below.

Detection Methods for CVE-2024-56614

Indicators of Compromise

Kernel oops or page fault messages referencing xsk_map_delete_elem in dmesg or /var/log/kern.log
Unexpected kernel panics with BUG: unable to handle page fault traces involving BPF map operations
Processes invoking bpf() syscall with BPF_MAP_DELETE_ELEM against XSK maps from non-administrative users

Detection Strategies

Monitor audit logs for bpf() syscall activity, particularly map deletion operations targeting BPF_MAP_TYPE_XSKMAP
Deploy eBPF-based runtime monitoring to flag negative key values passed to XSK map operations
Correlate kernel crash reports with recent BPF activity to identify post-exploitation traces

Monitoring Recommendations

Enable auditd rules for the bpf syscall and review entries with suspicious argument patterns
Track kernel version inventory across Linux fleet to identify unpatched hosts
Alert on kernel oops events containing xsk_map symbols in stack traces

How to Mitigate CVE-2024-56614

Immediate Actions Required

Apply the upstream kernel patches from the stable tree commits referenced in the kernel.org advisories
Update to a patched distribution kernel package, including the Debian LTS update for affected releases
Restrict unprivileged access to the bpf() syscall by setting kernel.unprivileged_bpf_disabled=1

Patch Information

The fix has been merged into the upstream Linux kernel across multiple stable branches. Refer to the relevant commits: Kernel Git Commit 32cd3db7, Kernel Git Commit 4d03f705, Kernel Git Commit d486b574, Kernel Git Commit ed08c93d, and Kernel Git Commit f8abd03f. Debian users should consult the Debian LTS Announcement.

Workarounds

Disable unprivileged BPF using the sysctl kernel.unprivileged_bpf_disabled=1 until patches are applied
Remove CAP_BPF and CAP_NET_ADMIN from non-essential workloads to limit XSK map creation
Apply seccomp filters to block the bpf() syscall for untrusted processes and containers

bash

# Configuration example - disable unprivileged BPF
sudo sysctl -w kernel.unprivileged_bpf_disabled=1
echo 'kernel.unprivileged_bpf_disabled=1' | sudo tee -a /etc/sysctl.d/99-bpf-hardening.conf
sudo sysctl --system