CVE-2022-39190: Linux Kernel DOS Vulnerability

CVE-2022-39190 Overview

An issue was discovered in net/netfilter/nf_tables_api.c in the Linux kernel before version 5.19.6. A denial of service vulnerability exists that can occur when a process attempts to bind to an already bound chain in the netfilter subsystem. This flaw in the nf_tables API allows local attackers with limited privileges to trigger a denial of service condition by exploiting improper validation of chain binding states.

Critical Impact

Local attackers can cause system denial of service by binding to already bound chains in the netfilter nf_tables subsystem, potentially disrupting network filtering operations and system availability.

Affected Products

• Linux Kernel versions prior to 5.19.6
• Debian Linux 10.0

Discovery Timeline

• 2022-09-02 - CVE CVE-2022-39190 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2022-39190

Vulnerability Analysis

The vulnerability resides in the netfilter nf_tables subsystem, specifically within the nf_tables_api.c file. The root issue stems from missing validation logic that should prevent binding operations to chains that are already in a bound state. When a local user with appropriate capabilities attempts to bind to an already bound chain, the system fails to properly reject this operation, leading to a denial of service condition.

The netfilter framework in Linux provides packet filtering, network address translation (NAT), and packet mangling capabilities. The nf_tables component is the modern replacement for iptables and provides a more flexible and efficient framework for network packet classification. Chain binding is a critical operation in this framework, and improper handling of binding states can lead to resource exhaustion or system instability.

Root Cause

The vulnerability exists because the nf_tables API lacks proper validation to check whether a chain is already bound before allowing additional binding operations. The nft_chain_is_bound() function was not being called to verify the chain's binding state prior to permitting the binding request. This oversight allows duplicate binding operations that the system is not designed to handle gracefully.

Attack Vector

The attack requires local access with low privileges on the target system. An attacker must have the ability to interact with the netfilter subsystem, typically through netlink sockets. The attacker can exploit this vulnerability by issuing binding requests to chains that are already bound, causing the system to enter an inconsistent state that results in denial of service.

 		return PTR_ERR(chain);
 	if (nft_is_base_chain(chain))
 		return -EOPNOTSUPP;
+	if (nft_chain_is_bound(chain))
+		return -EINVAL;
 	if (desc->flags & NFT_DATA_DESC_SETELEM &&
 	    chain->flags & NFT_CHAIN_BINDING)
 		return -EINVAL;

Source: GitHub Linux Commit e02f0d3

The patch adds a critical check using nft_chain_is_bound() to verify whether the chain is already bound before proceeding with the binding operation. If the chain is already bound, the function now returns -EINVAL to reject the request.

Detection Methods for CVE-2022-39190

Indicators of Compromise

• Unexpected system crashes or kernel panics related to netfilter operations
• Repeated failed netfilter chain binding operations in system logs
• Abnormal resource consumption in processes interacting with nf_tables
• Degraded network performance or packet filtering failures

Detection Strategies

• Monitor kernel logs for netfilter-related errors or warnings using dmesg or /var/log/kern.log
• Implement auditing of netlink socket operations to detect unusual nf_tables interactions
• Use kernel tracing tools like ftrace or bpftrace to monitor nf_tables API calls
• Deploy intrusion detection rules to identify suspicious local privilege activity targeting netfilter

Monitoring Recommendations

• Enable kernel auditing for CAP_NET_ADMIN capability usage to track privileged network operations
• Monitor for processes making unusual numbers of netfilter configuration changes
• Implement baseline monitoring for normal nf_tables operations to identify anomalies
• Configure alerting for kernel-level denial of service indicators

How to Mitigate CVE-2022-39190

Immediate Actions Required

• Update the Linux kernel to version 5.19.6 or later immediately
• Review systems for any signs of exploitation or denial of service incidents
• Restrict access to netfilter configuration capabilities to only trusted users and processes
• Consider implementing additional access controls on systems that cannot be immediately patched

Patch Information

The vulnerability has been addressed in Linux kernel version 5.19.6. The fix was implemented in commit e02f0d3970404bfea385b6edb86f2d936db0ea2b, which adds validation to check if a chain is already bound before allowing binding operations. Detailed information about the fix is available in the Linux Kernel ChangeLog 5.19.6 and the GitHub Linux Commit e02f0d3.

Debian users should refer to the Debian LTS Announcement November 2022 for distribution-specific patch information.

Workarounds

• Limit local user access to systems running vulnerable kernel versions
• Restrict CAP_NET_ADMIN capability to reduce the attack surface
• Implement namespace isolation to contain potential exploitation attempts
• Consider using security modules like AppArmor or SELinux to restrict nf_tables access

# Configuration example: Restrict CAP_NET_ADMIN capability
# Remove CAP_NET_ADMIN from processes that don't require it
setcap -r /path/to/binary

# Verify kernel version is patched
uname -r
# Should show 5.19.6 or later

# Check for available kernel updates on Debian
apt update && apt list --upgradable | grep linux-image