CVE-2022-2586: Linux Kernel Use-After-Free Vulnerability

CVE-2022-2586 Overview

CVE-2022-2586 is a use-after-free vulnerability in the Linux kernel's nftables subsystem. The flaw exists because an nft object or expression can reference an nft set on a different nft table. When that referenced table is deleted, the original object or expression retains a dangling pointer to freed memory, resulting in a use-after-free condition. This vulnerability can be exploited by a local attacker with limited privileges to achieve privilege escalation, potentially gaining root access on vulnerable systems.

Critical Impact

This vulnerability is actively exploited in the wild and is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog. Local attackers can leverage this flaw to escalate privileges and gain complete control over affected Linux systems.

Affected Products

• Linux Kernel versions prior to the security patch
• Canonical Ubuntu Linux 14.04 ESM
• Canonical Ubuntu Linux 16.04 ESM
• Canonical Ubuntu Linux 18.04 ESM
• Canonical Ubuntu Linux 20.04 LTS
• Canonical Ubuntu Linux 22.04 LTS

Discovery Timeline

• 2024-01-08 - CVE-2022-2586 published to NVD
• 2025-10-28 - Last updated in NVD database

Technical Details for CVE-2022-2586

Vulnerability Analysis

This vulnerability resides in the netfilter (nftables) subsystem of the Linux kernel, which is responsible for packet filtering and network address translation. The core issue stems from improper cross-table reference handling within nftables.

When an nft object or expression is created, it can reference an nft set that belongs to a different nft table. The vulnerability occurs because the kernel does not properly validate or track these cross-table references. If the table containing the referenced set is deleted, the memory associated with that set is freed. However, the original object or expression still maintains a pointer to the now-freed memory location.

Subsequent operations on the dangling reference trigger a use-after-free condition (CWE-416), which can lead to memory corruption. Attackers with local access and limited privileges (such as the ability to create and manipulate nftables rules) can craft a specific sequence of netfilter operations to trigger this vulnerability and escalate their privileges to root.

Root Cause

The root cause of CVE-2022-2586 is inadequate reference counting and lifetime management for nft sets when they are referenced across different nft tables. The kernel's nftables implementation failed to ensure that cross-table references properly increment reference counts or validate that referenced objects still exist before use. This oversight allows a table deletion to free memory that is still being referenced by objects in other tables, creating the use-after-free condition.

Attack Vector

The attack vector for this vulnerability is local, requiring an attacker to have authenticated access to the system with the ability to interact with the nftables subsystem. The exploitation process involves:

1. Creating two separate nft tables
2. Creating an nft set in the first table
3. Creating an object or expression in the second table that references the set in the first table
4. Deleting the first table, freeing the referenced set's memory
5. Triggering access to the now-dangling reference, causing use-after-free
6. Leveraging the memory corruption to achieve privilege escalation

The attack does not require user interaction and can be executed with low-privileged user access, making it particularly dangerous in multi-tenant environments or systems where users have shell access.

Detection Methods for CVE-2022-2586

Indicators of Compromise

• Unexpected kernel crashes or panics related to netfilter/nftables operations
• Suspicious processes running with elevated privileges that originated from unprivileged users
• Unusual nftables rule modifications or table creation/deletion patterns in system logs
• Memory corruption errors in kernel logs associated with the nf_tables module

Detection Strategies

• Monitor for suspicious nftables operations using auditd rules targeting netfilter-related system calls
• Implement kernel auditing to track nft command execution and table manipulation activities
• Deploy endpoint detection solutions capable of identifying privilege escalation attempts
• Review system logs for unexpected changes in process privilege levels

Monitoring Recommendations

• Enable kernel auditing for netfilter subsystem operations (CONFIG_NETFILTER_NETLINK and related options)
• Configure monitoring for new root processes spawned from non-privileged parent processes
• Implement runtime detection for use-after-free exploitation patterns in memory operations
• Deploy SentinelOne agents for real-time behavioral detection of privilege escalation attempts

How to Mitigate CVE-2022-2586

Immediate Actions Required

• Apply the latest kernel security updates from your Linux distribution immediately
• Restrict access to nftables management capabilities using user namespaces and capabilities
• Review and audit user accounts with access to netfilter operations
• Consider temporarily disabling unprivileged user namespaces if not required (kernel.unprivileged_userns_clone=0)

Patch Information

The vulnerability has been addressed through kernel patches that implement proper reference tracking for cross-table nft set references. Security updates are available from multiple vendors:

• Linux Kernel: Refer to the Kernel Development Discussion for the official patch
• Ubuntu: Multiple security notices have been released including USN-5557-1, USN-5560-1, and USN-5567-1
• Additional Information: See the ZDI-22-1118 Advisory for detailed technical analysis

Organizations should prioritize patching given this vulnerability's presence in the CISA Known Exploited Vulnerabilities Catalog.

Workarounds

• Restrict nftables access to trusted administrators only by limiting CAP_NET_ADMIN capability
• Disable unprivileged user namespaces to prevent unprivileged users from accessing nftables
• Implement strict access controls on systems where kernel updates cannot be immediately applied
• Use containerization with restricted namespace access to limit exposure

# Disable unprivileged user namespaces (temporary mitigation)
echo 0 > /proc/sys/kernel/unprivileged_userns_clone

# Or persist via sysctl configuration
echo "kernel.unprivileged_userns_clone = 0" >> /etc/sysctl.d/99-security.conf
sysctl -p /etc/sysctl.d/99-security.conf