CVE-2026-22184: zlib Buffer Overflow Vulnerability

CVE-2026-22184 Overview

A critical global buffer overflow vulnerability has been discovered in zlib versions up to and including 1.3.1.2. The vulnerability exists in the untgz utility, specifically within the TGZfname() function. This function copies an attacker-supplied archive name from argv[] into a fixed-size 1024-byte static global buffer using an unbounded strcpy() call without proper length validation. When an archive name exceeding 1024 bytes is supplied, an out-of-bounds write occurs, potentially leading to memory corruption, denial of service, and code execution.

Critical Impact

This buffer overflow vulnerability can be exploited prior to any archive parsing or validation, allowing attackers to potentially achieve remote code execution or cause denial of service through memory corruption.

Affected Products

• zlib versions up to and including 1.3.1.2
• Applications and systems utilizing the untgz utility from vulnerable zlib versions
• Linux distributions and software packages bundling affected zlib versions

Discovery Timeline

• 2026-01-07 - CVE-2026-22184 published to NVD
• 2026-01-08 - Last updated in NVD database

Technical Details for CVE-2026-22184

Vulnerability Analysis

This vulnerability is classified as CWE-120 (Buffer Copy without Checking Size of Input), a classic buffer overflow condition. The vulnerability occurs in the TGZfname() function within the untgz utility, which is responsible for handling archive filenames. The function uses a static global buffer of 1024 bytes to store the archive name but fails to validate the length of the input before performing the copy operation.

The exploitation potential depends on several environmental factors including compiler optimizations, build flags, target architecture, and memory layout. Since the vulnerable buffer is a global static variable, successful exploitation could allow an attacker to overwrite adjacent global variables or function pointers, potentially leading to arbitrary code execution.

Root Cause

The root cause of this vulnerability is the use of the unsafe strcpy() function without any bounds checking. The TGZfname() function directly copies user-controlled input from command-line arguments into a fixed-size buffer without validating that the input length does not exceed the buffer capacity. This represents a fundamental secure coding violation where user input is trusted without validation.

Attack Vector

The vulnerability is network-exploitable when the untgz utility processes filenames from remote sources or when applications pass untrusted input to the utility. An attacker can craft a malicious archive name exceeding 1024 bytes to trigger the buffer overflow. The attack surface includes any scenario where untrusted archive names are processed by the vulnerable utility, including web applications that handle user-uploaded archives, automated build systems processing external archives, and file extraction services.

The overflow occurs immediately when the filename is processed, before any archive content validation takes place, making it particularly dangerous as it cannot be prevented by validating archive contents.

Detection Methods for CVE-2026-22184

Indicators of Compromise

• Unexpected crashes or segmentation faults in processes using the untgz utility
• Core dumps indicating memory corruption in zlib-related functions
• Abnormally long filenames (exceeding 1024 bytes) in archive processing logs
• Evidence of exploitation attempts through unusually long command-line arguments

Detection Strategies

• Monitor for processes executing untgz with excessively long arguments
• Implement memory corruption detection tools such as AddressSanitizer in development and testing environments
• Deploy endpoint protection capable of detecting buffer overflow exploitation attempts
• Review application logs for evidence of archive processing failures with long filenames

Monitoring Recommendations

• Enable system auditing for command-line argument lengths exceeding normal thresholds
• Implement file integrity monitoring for critical system binaries that link against zlib
• Configure SIEM rules to alert on unusual untgz utility invocations
• Monitor for memory corruption signatures in endpoint protection solutions

How to Mitigate CVE-2026-22184

Immediate Actions Required

• Identify all systems and applications using zlib versions 1.3.1.2 or earlier
• Review applications that utilize the untgz utility and assess exposure to untrusted input
• Implement input validation at the application layer to restrict filename lengths before passing to zlib utilities
• Consider disabling or restricting access to the untgz utility where not required

Patch Information

Organizations should monitor the zlib official website and GitHub zlib repository for security updates addressing this vulnerability. The VulnCheck Advisory for zlib and Full Disclosure post provide additional technical details and remediation guidance.

Workarounds

• Implement application-level input validation to ensure archive filenames do not exceed 1023 bytes before processing
• Use wrapper scripts or security controls to validate command-line argument lengths
• Deploy runtime application self-protection (RASP) solutions capable of detecting buffer overflow attempts
• Consider using alternative archive extraction utilities until a patch is available
• Compile applications with stack canaries and ASLR enabled to reduce exploitation likelihood

# Configuration example - Input validation wrapper for untgz
# Validate filename length before calling untgz utility
MAX_FILENAME_LENGTH=1000
if [ ${#1} -gt $MAX_FILENAME_LENGTH ]; then
    echo "Error: Filename exceeds safe length limit"
    exit 1
fi