CVE-2023-32233: Linux Kernel Privilege Escalation Flaw

CVE-2023-32233 Overview

CVE-2023-32233 is a use-after-free vulnerability in the Linux kernel's Netfilter nf_tables subsystem that allows unprivileged local users to escalate privileges to root. The vulnerability exists in kernel versions through 6.3.1 and occurs when processing batch requests, enabling attackers to perform arbitrary read and write operations on kernel memory. The root cause is the mishandling of anonymous sets within the Netfilter framework.

Critical Impact

Local privilege escalation to root on affected Linux systems through kernel memory corruption in the Netfilter subsystem.

Affected Products

• Linux Kernel (through version 6.3.1)
• Red Hat Enterprise Linux 7.0, 8.0, and 9.0
• NetApp HCI Baseboard Management Controller (H300s, H410c, H410s, H500s, H700s)

Discovery Timeline

• 2023-05-08 - CVE-2023-32233 published to NVD
• 2025-05-05 - Last updated in NVD database

Technical Details for CVE-2023-32233

Vulnerability Analysis

This use-after-free vulnerability resides in the Netfilter nf_tables component, which is responsible for packet filtering, NAT, and other packet mangling operations in the Linux kernel. The flaw specifically affects how anonymous sets are handled during batch request processing.

When batch requests are processed by nf_tables, the code fails to properly manage the lifecycle of anonymous sets. Anonymous sets are temporary data structures used during rule evaluation. The vulnerability allows an attacker to trigger a condition where a set is freed while still being referenced, creating a classic use-after-free scenario. An attacker with local access can exploit this by crafting specific Netfilter batch operations that manipulate the timing and order of set operations.

Once the use-after-free condition is triggered, the attacker can potentially allocate new kernel objects in the freed memory region, enabling arbitrary read and write primitives in kernel memory space. This capability can be leveraged to overwrite critical kernel data structures, disable security mechanisms, or directly escalate privileges to root.

Root Cause

The vulnerability stems from improper deactivation handling of anonymous sets during the transaction preparation phase. Anonymous sets were not being properly deactivated during the NFT_TRANS_PREPARE phase, leading to a race condition where the set could be freed while still accessible. The fix introduces proper lifecycle management by calling nft_deactivate_next() for anonymous sets during the preparation phase.

Attack Vector

The attack requires local access to the system with the ability to interact with the Netfilter subsystem. An unprivileged user can exploit this vulnerability through the Netfilter netlink interface by:

1. Creating Netfilter rules with anonymous sets
2. Submitting carefully crafted batch requests that trigger the use-after-free condition
3. Timing memory allocation to reclaim the freed set memory
4. Using the corrupted memory state to achieve arbitrary kernel read/write
5. Escalating privileges to root by modifying kernel credentials or security structures

// Patch from net/netfilter/nf_tables_api.c
// Source: https://github.com/torvalds/linux/commit/c1592a89942e9678f7d9c8030efa777c0d57edab

void nf_tables_activate_set(const struct nft_ctx *ctx, struct nft_set *set)
{
	if (nft_set_is_anonymous(set))
		nft_clear(ctx->net, set);

	set->use++;
}
EXPORT_SYMBOL_GPL(nf_tables_activate_set);

void nf_tables_deactivate_set(const struct nft_ctx *ctx, struct nft_set *set,
			      struct nft_set_binding *binding,
			      enum nft_trans_phase phase)
{
	switch (phase) {
	case NFT_TRANS_PREPARE:
		if (nft_set_is_anonymous(set))
			nft_deactivate_next(ctx->net, set);

		set->use--;
		return;
	case NFT_TRANS_ABORT:

Source: GitHub Linux Commit Update

Detection Methods for CVE-2023-32233

Indicators of Compromise

• Unexpected system crashes or kernel panics related to Netfilter or nf_tables subsystems
• Unusual process privilege changes where unprivileged processes suddenly gain root access
• Suspicious Netfilter netlink socket activity from non-administrative user accounts
• Kernel log messages indicating memory corruption or use-after-free conditions in nf_tables

Detection Strategies

• Monitor for anomalous Netfilter configuration changes using auditd rules on netlink sockets
• Implement kernel-level monitoring for suspicious nf_tables batch operations
• Deploy SentinelOne agents with kernel-level visibility to detect privilege escalation attempts
• Review system logs for unusual patterns of Netfilter rule creation and deletion

Monitoring Recommendations

• Enable kernel auditing for Netfilter subsystem calls and netlink socket operations
• Configure alerting for any process that unexpectedly gains elevated privileges
• Monitor for rapid creation and deletion of Netfilter anonymous sets
• Implement real-time kernel integrity monitoring to detect memory corruption

How to Mitigate CVE-2023-32233

Immediate Actions Required

• Update Linux kernel to a patched version immediately on all affected systems
• Apply vendor-provided security patches from Red Hat, Debian, or your distribution
• Restrict local user access on critical systems until patches are applied
• Consider enabling kernel live patching solutions for zero-downtime remediation

Patch Information

The vulnerability has been addressed in kernel commit c1592a89942e9678f7d9c8030efa777c0d57edab. The fix modifies the nf_tables_deactivate_set() function to properly deactivate anonymous sets during the NFT_TRANS_PREPARE phase by calling nft_deactivate_next(). Additionally, a new function nf_tables_activate_set() was introduced to properly handle set activation for anonymous sets.

Patches are available from multiple sources:

• Linux Kernel Commit Change
• Red Hat Bug Report
• Debian Security Advisory DSA-5402
• Kernel Live Patch Security Notice LSN-0095-1

Workarounds

• Restrict access to the Netfilter netlink interface using namespace isolation or SELinux policies
• Limit local user accounts on sensitive systems to reduce the attack surface
• Deploy additional monitoring on systems where immediate patching is not feasible
• Consider using seccomp filters to restrict access to Netfilter-related system calls for untrusted processes

# Check current kernel version
uname -r

# Verify if nf_tables module is loaded
lsmod | grep nf_tables

# Restrict nf_tables access via module blacklisting (temporary workaround)
echo "blacklist nf_tables" >> /etc/modprobe.d/blacklist-nftables.conf

# Update kernel packages (Debian/Ubuntu)
apt update && apt upgrade linux-image-$(uname -r)

# Update kernel packages (RHEL/CentOS)
yum update kernel