CVE-2023-4156: GNU Gawk Buffer Overflow Vulnerability

CVE-2023-4156 Overview

A heap out-of-bounds read vulnerability has been discovered in the builtin.c file of the GNU Gawk package. This memory corruption flaw allows attackers to read data beyond the allocated heap buffer boundaries, potentially leading to application crashes and unauthorized access to sensitive information stored in memory.

Critical Impact

This vulnerability can be exploited locally to cause denial of service through application crashes and potentially leak sensitive memory contents, affecting systems running vulnerable versions of GNU Gawk across multiple Linux distributions.

Affected Products

• GNU Gawk (all vulnerable versions)
• Red Hat Enterprise Linux 6.0
• Red Hat Enterprise Linux 7.0
• Fedora 38

Discovery Timeline

• September 25, 2023 - CVE-2023-4156 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2023-4156

Vulnerability Analysis

The vulnerability exists within the builtin.c source file of GNU Gawk, a powerful pattern scanning and text processing utility. The flaw is classified as CWE-125 (Out-of-bounds Read), indicating that the program reads data past the end or before the beginning of an intended buffer.

The exploitation requires local access with user interaction, meaning an attacker would need to convince a user to process a maliciously crafted input file with gawk. Upon successful exploitation, the attacker can potentially extract sensitive information from memory or cause the application to crash, resulting in a denial of service condition.

GNU Gawk is widely deployed across Linux distributions for text processing tasks, scripting, and data manipulation, making this vulnerability relevant to system administrators and developers who rely on gawk for automation tasks.

Root Cause

The root cause of this vulnerability lies in improper bounds checking within the builtin.c file. When processing certain inputs, the code fails to properly validate buffer boundaries before performing read operations on heap-allocated memory. This allows read operations to access memory locations outside the intended buffer, leading to the out-of-bounds read condition.

Attack Vector

The attack vector for CVE-2023-4156 is local, requiring an attacker to either have direct access to the target system or to craft a malicious input file that a legitimate user would process with gawk. The exploitation scenario typically involves:

1. The attacker creates a specially crafted AWK script or input data file designed to trigger the heap out-of-bounds read condition
2. The victim executes gawk to process the malicious input
3. The vulnerability is triggered during the parsing or execution phase within builtin.c
4. Depending on the memory layout, the attacker may extract sensitive data from adjacent heap memory or cause the application to crash

For detailed technical information, refer to the Red Hat CVE-2023-4156 Advisory and Red Hat Bug #2215930.

Detection Methods for CVE-2023-4156

Indicators of Compromise

• Unexpected gawk process crashes or segmentation faults during script execution
• Core dumps generated by gawk processes containing potential memory access violations
• Unusual error messages related to memory operations in gawk execution logs
• Presence of suspicious or malformed AWK script files on the system

Detection Strategies

• Monitor system logs for repeated gawk crashes or abnormal termination events
• Implement file integrity monitoring on critical AWK scripts to detect tampering
• Use address sanitizer tools (ASAN) during development to identify out-of-bounds memory access patterns
• Deploy endpoint detection solutions to identify anomalous gawk behavior patterns

Monitoring Recommendations

• Enable crash dump collection and analysis for gawk processes to identify exploitation attempts
• Monitor for unusual patterns of gawk invocations, especially with untrusted input files
• Implement audit logging for command execution involving gawk with external inputs
• Review and validate AWK scripts from untrusted sources before execution

How to Mitigate CVE-2023-4156

Immediate Actions Required

• Update GNU Gawk to the latest patched version available for your distribution
• Review and audit any AWK scripts processing untrusted or external input data
• Restrict execution of gawk with untrusted inputs until patches are applied
• Consider using containerization or sandboxing for gawk operations processing external data

Patch Information

Red Hat has tracked this vulnerability and provides security guidance through their advisory system. System administrators should check their distribution's package repositories for updated gawk packages that address this vulnerability.

For Red Hat Enterprise Linux users, consult the Red Hat CVE-2023-4156 Advisory for specific remediation instructions. Fedora users should update to patched packages when available through the standard update channels.

Workarounds

• Validate and sanitize all input data before processing with gawk
• Run gawk processes with minimal privileges using dedicated service accounts
• Implement input file size and complexity limits to reduce attack surface
• Use application sandboxing mechanisms such as SELinux or AppArmor to contain potential exploitation

# Example: Restrict gawk execution with reduced privileges
# Create a dedicated user for gawk operations
useradd -r -s /sbin/nologin gawk-runner

# Run gawk with restricted privileges
sudo -u gawk-runner gawk -f script.awk input.txt

# Enable SELinux enforcement for additional protection
setenforce 1