CVE-2023-42753: Linux Kernel Privilege Escalation Flaw

CVE-2023-42753 Overview

An array indexing vulnerability was discovered in the netfilter subsystem of the Linux kernel. A missing macro leads to a miscalculation of the h->nets array offset, providing attackers with the primitive to arbitrarily increment or decrement a memory buffer out-of-bound. This vulnerability enables local users to crash the system or potentially escalate their privileges.

Critical Impact

Local privilege escalation and denial of service affecting multiple Linux kernel versions across major enterprise distributions including Red Hat Enterprise Linux and Debian Linux.

Affected Products

• Linux Kernel (multiple versions)
• Red Hat Enterprise Linux 7.0, 8.0, 9.0
• Debian Linux 10.0

Discovery Timeline

• September 22, 2023 - Vulnerability disclosed via Openwall OSS-Security mailing list
• September 25, 2023 - CVE-2023-42753 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2023-42753

Vulnerability Analysis

The vulnerability exists within the netfilter subsystem, specifically in the IP set hash network type implementation. A missing macro in the codebase causes incorrect calculation of the h->nets array offset. This miscalculation creates an out-of-bounds memory access condition that allows attackers to perform arbitrary increment and decrement operations on memory locations outside the intended buffer boundaries.

The netfilter subsystem is a core Linux kernel component responsible for packet filtering, network address translation (NAT), and other packet mangling operations. The affected code path handles IP set operations where network addresses are stored and managed in hash tables. When processing certain operations, the missing macro causes the kernel to compute an incorrect index into the h->nets array, leading to memory corruption.

Root Cause

The root cause is classified as CWE-787 (Out-of-bounds Write). The vulnerability stems from a missing macro that should properly calculate array offsets within the netfilter IP set hash implementation. Without this macro, the kernel miscalculates memory boundaries when accessing the h->nets array structure, allowing operations to occur outside the allocated memory region.

Attack Vector

Exploitation requires local access to the target system. An attacker with low privileges can trigger the vulnerable code path through netfilter operations, causing the kernel to perform out-of-bounds memory writes. The attacker can leverage the arbitrary increment/decrement primitive to:

1. Corrupt kernel memory structures to achieve denial of service (system crash)
2. Manipulate control data or function pointers to achieve privilege escalation
3. Modify security-critical kernel structures to bypass access controls

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

Detection Methods for CVE-2023-42753

Indicators of Compromise

• Unexpected system crashes or kernel panics related to netfilter or IP set operations
• Suspicious processes attempting to manipulate netfilter configurations
• Unusual privilege escalation events from low-privileged users
• Kernel oops or BUG messages referencing netfilter or ipset subsystems

Detection Strategies

• Monitor kernel logs for oops messages containing references to nf_tables, ip_set, or hash:net functions
• Deploy kernel auditing rules to track netfilter-related system calls from non-root users
• Implement behavioral analysis to detect processes attempting repeated netfilter operations in rapid succession
• Use SentinelOne's kernel-level monitoring to detect anomalous memory access patterns

Monitoring Recommendations

• Enable kernel auditing for netfilter and ipset operations using auditd rules
• Configure alerting for unexpected kernel crashes or restarts
• Monitor for privilege escalation attempts following netfilter operations
• Review user activity logs for suspicious ipset or iptables command usage

How to Mitigate CVE-2023-42753

Immediate Actions Required

• Apply the latest kernel security updates from your distribution vendor immediately
• Restrict access to netfilter and ipset operations to trusted administrators only
• Implement network segmentation to limit exposure of vulnerable systems
• Monitor affected systems for signs of exploitation until patches are applied

Patch Information

Multiple vendors have released security patches to address this vulnerability. Red Hat has issued extensive security advisories including RHSA-2023:7370, RHSA-2023:7379, RHSA-2023:7382, and numerous others through early 2024. Debian has published Long Term Support announcements via Debian LTS Announcement #2023-10-27 and Debian LTS Announcement #2024-01-04. Kernel Live Patch information is available through Packet Storm Security Notice LSN-0099-1. Consult your distribution's security advisories for specific patch versions.

Workarounds

• Limit local user access on systems where patching is not immediately possible
• Use kernel security modules (SELinux, AppArmor) to restrict netfilter access to privileged processes
• Consider disabling unused IP set types if operationally feasible
• Implement strict user access controls and remove unnecessary local accounts

# Restrict ipset access using capabilities (example for limiting exposure)
# Check current kernel version
uname -r

# Verify if netfilter modules are loaded
lsmod | grep -E "nf_tables|ip_set"

# Apply Red Hat kernel updates
yum update kernel kernel-devel

# Apply Debian kernel updates  
apt-get update && apt-get upgrade linux-image-*