CVE-2023-3390: Linux Kernel Use-After-Free Vulnerability

CVE-2023-3390 Overview

A use-after-free vulnerability was discovered in the Linux kernel's netfilter subsystem within net/netfilter/nf_tables_api.c. The flaw stems from mishandled error handling with NFT_MSG_NEWRULE, which allows a dangling pointer to be used within the same transaction, resulting in a use-after-free condition. This vulnerability enables a local attacker with user access to escalate privileges on the affected system.

Critical Impact

Local attackers with user-level access can exploit this use-after-free vulnerability to achieve full privilege escalation, potentially gaining root access to the Linux system.

Affected Products

• Linux Linux Kernel
• NetApp H300S
• NetApp H410C
• NetApp H410S
• NetApp H500S
• NetApp H700S

Discovery Timeline

• June 28, 2023 - CVE-2023-3390 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2023-3390

Vulnerability Analysis

This vulnerability is classified as CWE-416 (Use After Free), a memory corruption issue where the application references memory after it has been freed. In the context of the Linux kernel's netfilter subsystem, the vulnerability occurs within the nf_tables API, which is responsible for managing netfilter table rules.

The core issue lies in how the NFT_MSG_NEWRULE message handler processes error conditions. When an error occurs during rule creation, the error handling code fails to properly manage memory references, leaving a dangling pointer that can be reused within the same transaction. This creates a window where freed memory can be accessed and potentially manipulated by an attacker.

Since netfilter operates within kernel space and handles network packet filtering, successful exploitation grants the attacker elevated privileges at the kernel level. The local attack vector requires user-level access, but the impact extends to full confidentiality, integrity, and availability compromise of the system.

Root Cause

The root cause is improper error handling in the nf_tables_api.c component of the netfilter subsystem. When NFT_MSG_NEWRULE encounters an error condition, the code does not correctly invalidate or handle the pointer to the rule object being created. This leaves a dangling pointer that references deallocated memory, which can subsequently be dereferenced within the same transaction context, leading to the use-after-free condition.

Attack Vector

The attack requires local access to the system with at least user-level privileges. An attacker can trigger the vulnerability by:

1. Interacting with the netfilter subsystem through netlink sockets
2. Crafting specific NFT_MSG_NEWRULE messages that trigger the error handling path
3. Exploiting the dangling pointer during the same transaction to corrupt kernel memory
4. Leveraging the memory corruption to escalate privileges to root

The vulnerability is exploited through crafted netlink messages to the netfilter subsystem. When the NFT_MSG_NEWRULE handler encounters specific error conditions, it leaves a dangling pointer that can be reused within the same transaction. An attacker can manipulate this behavior to corrupt kernel memory structures and achieve privilege escalation. For detailed technical information, refer to the Kernel Git Commit Details.

Detection Methods for CVE-2023-3390

Indicators of Compromise

• Unexpected privilege escalation events from low-privileged users to root
• Anomalous netlink socket activity targeting the netfilter subsystem (NFNL_SUBSYS_NFTABLES)
• Kernel crash logs or oops messages referencing nf_tables_api.c or netfilter components
• Suspicious processes gaining capabilities they should not possess

Detection Strategies

• Monitor system calls related to netlink socket creation and netfilter rule manipulation using auditd or eBPF-based tools
• Implement kernel integrity monitoring to detect unauthorized privilege changes
• Deploy endpoint detection and response (EDR) solutions capable of monitoring kernel-level activities
• Analyze kernel logs for use-after-free related crashes or memory corruption indicators

Monitoring Recommendations

• Enable comprehensive kernel auditing for netfilter-related operations
• Configure alerting for privilege escalation events, particularly from unprivileged users to root
• Monitor for unusual patterns in netfilter rule creation and deletion
• Implement system integrity verification to detect unauthorized kernel modifications

How to Mitigate CVE-2023-3390

Immediate Actions Required

• Apply the kernel patch identified by commit 1240eb93f0616b21c675416516ff3d74798fdc97 immediately
• Update to a patched kernel version from your Linux distribution vendor
• Review and restrict user access to netfilter/nftables functionality where possible
• Monitor systems for signs of exploitation until patches can be applied

Patch Information

The vulnerability is addressed in kernel commit 1240eb93f0616b21c675416516ff3d74798fdc97. Organizations should upgrade past this commit or apply distribution-specific security patches. Multiple vendors have released advisories and patches:

• Kernel Git Commit Details
• Debian Security Advisory DSA-5448
• Debian Security Advisory DSA-5461
• NetApp Security Advisory
• Kernel Live Patch Security Notice LSN-0097-1

Workarounds

• Restrict access to netfilter/nftables functionality using namespace isolation or capability restrictions
• Limit local user access to systems running vulnerable kernel versions
• Consider deploying kernel live patching solutions if immediate reboots are not feasible
• Implement network segmentation to limit the impact of potential privilege escalation

# Check current kernel version
uname -r

# For Debian/Ubuntu systems, update to patched kernel
sudo apt update && sudo apt upgrade linux-image-$(uname -r)

# Restrict nftables capabilities for non-root users (temporary mitigation)
# Note: This may impact legitimate netfilter usage
sudo setcap -r /usr/sbin/nft 2>/dev/null || true