CVE-2024-50262: Linux Kernel Buffer Overflow Vulnerability

CVE-2024-50262 Overview

CVE-2024-50262 is an out-of-bounds write vulnerability in the Linux kernel's BPF (Berkeley Packet Filter) subsystem. The vulnerability exists in the trie_get_next_key() function, which incorrectly allocates a node stack with size trie->max_prefixlen while potentially writing trie->max_prefixlen + 1 nodes to the stack when traversing full paths from root to leaves. This off-by-one error can lead to memory corruption, potentially enabling local privilege escalation or system crashes.

Critical Impact

Local attackers with low privileges can exploit this out-of-bounds write vulnerability to corrupt kernel memory, potentially achieving privilege escalation or causing system instability on affected Linux systems.

Affected Products

• Linux Kernel versions prior to patched releases
• Linux Kernel 6.12-rc1 through 6.12-rc5
• Various stable kernel branches requiring backported fixes

Discovery Timeline

• 2024-11-09 - CVE-2024-50262 published to NVD
• 2025-11-03 - Last updated in NVD database

Technical Details for CVE-2024-50262

Vulnerability Analysis

The vulnerability is a classic off-by-one error in memory allocation within the BPF trie data structure implementation. The trie_get_next_key() function is responsible for iterating through keys in a Longest Prefix Match (LPM) trie structure used by BPF programs. During this iteration, the function allocates a stack to track visited nodes during tree traversal.

The root cause lies in the calculation of the required stack size. The function allocates space for trie->max_prefixlen nodes, but when the trie contains a complete path from the root node through all prefix lengths to a leaf node, the actual number of nodes written is trie->max_prefixlen + 1. This discrepancy occurs because the allocation doesn't account for the root node in addition to all prefix-length nodes.

For instance, with a trie configured with max_prefixlen of 8, inserting nodes with keys 0x00/0, 0x00/1, 0x00/2, through 0x00/8 creates a full path of 9 nodes. When trie_get_next_key is called with a key having .prefixlen = 8, it attempts to write 9 nodes onto a stack sized for only 8, resulting in an out-of-bounds write.

Root Cause

The vulnerability stems from an incorrect buffer size calculation in the trie_get_next_key() function. The allocated node stack uses trie->max_prefixlen as its size, but the actual maximum number of nodes that can be written during traversal is trie->max_prefixlen + 1 due to the inclusion of the root node. This off-by-one allocation error is classified as CWE-787 (Out-of-bounds Write).

Attack Vector

The attack requires local access to the system with the ability to interact with BPF maps. An attacker would need to:

1. Create or access an LPM trie BPF map with a specific max_prefixlen configuration
2. Insert a carefully crafted sequence of keys that creates a full path from root to leaf
3. Trigger the trie_get_next_key() operation to cause the out-of-bounds write
4. Leverage the memory corruption for privilege escalation or denial of service

The vulnerability requires local access and low privileges, making it exploitable by unprivileged users on systems where BPF functionality is accessible. The exploitation can lead to high impact on confidentiality, integrity, and availability as kernel memory can be corrupted.

Detection Methods for CVE-2024-50262

Indicators of Compromise

• Unexpected kernel crashes or oops messages related to BPF trie operations
• Memory corruption errors in kernel logs referencing trie_get_next_key or LPM map functions
• Unusual BPF map operations from unprivileged processes attempting to access LPM trie maps

Detection Strategies

• Monitor for kernel panic or oops messages containing references to trie_get_next_key, bpf, or LPM trie functions
• Implement audit logging for BPF syscalls and map operations, particularly focusing on LPM trie map types
• Use kernel address sanitizer (KASAN) in development environments to detect out-of-bounds writes during testing

Monitoring Recommendations

• Enable kernel auditing for BPF-related syscalls (bpf() syscall)
• Configure crash dump collection to capture kernel state for post-incident analysis
• Monitor system logs for signs of memory corruption or unexpected kernel behavior related to networking subsystems

How to Mitigate CVE-2024-50262

Immediate Actions Required

• Update the Linux kernel to a patched version that addresses CVE-2024-50262
• On systems where immediate patching is not possible, consider restricting BPF access through sysctl settings (kernel.unprivileged_bpf_disabled=1)
• Review systems for any signs of exploitation and monitor for unusual BPF activity

Patch Information

The Linux kernel maintainers have released patches across multiple stable branches. The fix increases the node stack allocation to properly account for the root node, preventing the out-of-bounds write condition. Patches are available through the following kernel git commits:

• Kernel Git Commit 13400ac
• Kernel Git Commit 590976f
• Kernel Git Commit 86c8ebe
• Kernel Git Commit 90a6e0e

Additionally, Debian LTS security announcements have been issued for affected distributions.

Workarounds

• Disable unprivileged BPF access by setting kernel.unprivileged_bpf_disabled=1 via sysctl
• Restrict access to BPF functionality through SELinux or AppArmor policies for untrusted users
• Limit container capabilities to prevent BPF operations from containerized workloads

# Disable unprivileged BPF access as a workaround
echo 1 > /proc/sys/kernel/unprivileged_bpf_disabled

# Make the setting persistent across reboots
echo "kernel.unprivileged_bpf_disabled=1" >> /etc/sysctl.conf
sysctl -p