CVE-2022-34918: Linux Kernel Privilege Escalation Flaw

CVE-2022-34918 Overview

CVE-2022-34918 is a type confusion vulnerability in the Linux kernel's Netfilter subsystem that can lead to local privilege escalation. The vulnerability exists in the nft_set_elem_init function within the nf_tables component, where improper type handling causes a buffer overflow condition. A local attacker with access to an unprivileged user namespace can exploit this flaw to obtain CAP_NET_ADMIN capabilities and ultimately escalate privileges to root access.

This vulnerability is distinct from CVE-2022-32250, another Netfilter-related privilege escalation issue. The flaw can be remediated through a patch applied to nft_setelem_parse_data in net/netfilter/nf_tables_api.c.

Critical Impact

Local privilege escalation to root access via type confusion in Netfilter nf_tables, requiring only unprivileged user namespace access to exploit.

Affected Products

• Linux Kernel through version 5.18.9
• Debian Linux 11.0
• Canonical Ubuntu Linux 14.04 LTS, 16.04 ESM, 18.04 LTS, 20.04 LTS, 22.04 LTS
• NetApp H300S, H500S, H700S, H410S, H410C (firmware)

Discovery Timeline

• 2022-07-04 - CVE-2022-34918 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2022-34918

Vulnerability Analysis

The vulnerability resides in the Netfilter nf_tables subsystem, specifically in how set element initialization handles type information. When processing set elements through nft_set_elem_init, the function fails to properly validate and handle type information, resulting in a type confusion condition. This type confusion subsequently causes a heap-based buffer overflow when the kernel attempts to process malformed data with incorrect type assumptions.

The exploitation path requires the attacker to first obtain CAP_NET_ADMIN capabilities, which can be achieved through access to an unprivileged user namespace. User namespaces allow unprivileged users to create isolated environments with elevated capabilities within that namespace. Once CAP_NET_ADMIN is obtained within a user namespace, the attacker can interact with the Netfilter subsystem and trigger the type confusion bug.

Root Cause

The root cause of this vulnerability is a type confusion bug (CWE-843) in the nft_set_elem_init function. The function improperly handles type validation when parsing data for set elements, allowing an attacker to supply data that the kernel incorrectly interprets. This mismatch between the expected type and the actual type provided leads to out-of-bounds memory operations when the kernel attempts to process the element data based on incorrect size or structure assumptions.

The fix addresses this issue in nft_setelem_parse_data within net/netfilter/nf_tables_api.c by implementing proper type validation before processing set element data.

Attack Vector

The attack requires local access to the target system. The attacker must first create or access an unprivileged user namespace to gain CAP_NET_ADMIN capabilities within that namespace. With these capabilities, the attacker can craft malicious Netfilter table operations that trigger the type confusion in nft_set_elem_init. The resulting buffer overflow can be leveraged to corrupt kernel memory structures, enabling arbitrary code execution in kernel context and ultimately achieving root privileges on the host system.

The attack flow involves:

1. Creating an unprivileged user namespace
2. Obtaining CAP_NET_ADMIN within the namespace
3. Crafting malicious nf_tables operations to trigger type confusion
4. Exploiting the heap overflow for privilege escalation

For detailed technical analysis and proof-of-concept information, see the RandoriSec Blog on Firewall and the Netfilter Privilege Escalation Exploit on Packet Storm.

Detection Methods for CVE-2022-34918

Indicators of Compromise

• Unexpected creation of user namespaces by low-privileged users
• Unusual nf_tables or Netfilter configuration changes from non-root processes
• Kernel crashes or instability related to netfilter subsystem operations
• Processes unexpectedly gaining root privileges after interacting with Netfilter

Detection Strategies

• Monitor for unshare or clone system calls with CLONE_NEWUSER flag from suspicious processes
• Audit Netfilter/nf_tables operations using Linux audit subsystem with rules targeting nft operations
• Deploy kernel integrity monitoring to detect unauthorized modifications to kernel memory
• Use SentinelOne's behavioral analysis to identify privilege escalation patterns following namespace creation

Monitoring Recommendations

• Enable kernel auditing for network namespace and Netfilter-related system calls
• Monitor /proc/[pid]/ns/user for unexpected user namespace creation
• Implement logging for all nftables rule modifications and set operations
• Configure alerts for processes that transition from unprivileged to root context

How to Mitigate CVE-2022-34918

Immediate Actions Required

• Apply kernel patches from your Linux distribution immediately
• Restrict user namespace creation by setting kernel.unprivileged_userns_clone=0 if not required
• Review and audit systems for signs of exploitation
• Consider deploying kernel live patches if available for your distribution

Patch Information

The vulnerability is fixed in the upstream Linux kernel. The specific fix is available in the Linux Kernel Commit Update with commit hash 7e6bc1f6cabcd30aba0b11219d8e01b952eacbb6. Distribution-specific patches are available:

• Debian: Debian Security Advisory DSA-5191
• Ubuntu: Kernel live patches available via Kernel Live Patch Security Notice LSN-0089-1
• NetApp: NetApp Security Advisory

Workarounds

• Disable unprivileged user namespace creation by setting kernel.unprivileged_userns_clone=0 in sysctl configuration
• Restrict access to the CAP_NET_ADMIN capability through strict namespace policies
• Implement seccomp filters to block namespace-related syscalls for untrusted applications
• Use container security policies to prevent namespace escape attempts

# Disable unprivileged user namespaces to mitigate exploitation
echo "kernel.unprivileged_userns_clone=0" >> /etc/sysctl.d/99-disable-userns.conf
sysctl -p /etc/sysctl.d/99-disable-userns.conf

# Verify the setting is applied
sysctl kernel.unprivileged_userns_clone