CVE-2023-46228: Zchunk Buffer Overflow Vulnerability

CVE-2023-46228 Overview

CVE-2023-46228 is an integer overflow vulnerability affecting zchunk, a library designed for creating and handling zchunk compressed files. The vulnerability exists in multiple components of the library, specifically in lib/comp/comp.c, lib/comp/zstd/zstd.c, lib/dl/multipart.c, and lib/header.c. When processing malformed zchunk files, the library fails to properly validate size calculations, leading to integer overflows that can result in memory corruption.

Critical Impact

Successful exploitation of this vulnerability through a maliciously crafted zchunk file can lead to arbitrary code execution, data corruption, or denial of service on systems using vulnerable versions of the zchunk library.

Affected Products

• zchunk versions prior to 1.3.2
• Linux distributions and applications that bundle or depend on the zchunk library
• Package managers and update mechanisms that utilize zchunk for delta compression

Discovery Timeline

• 2023-10-19 - CVE-2023-46228 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-46228

Vulnerability Analysis

The vulnerability arises from insufficient validation of size parameters when processing zchunk file data. Multiple functions within the zchunk library perform arithmetic operations on size values without checking for integer overflow conditions. When a malformed zchunk file contains specially crafted size values, these operations can wrap around, resulting in undersized memory allocations. Subsequent data operations then write beyond the allocated buffer boundaries, causing heap corruption.

The vulnerability requires local access and user interaction to exploit—an attacker must convince a user to open or process a malicious zchunk file. Once exploited, the impact is significant as it can lead to complete compromise of confidentiality, integrity, and availability of the affected system.

Root Cause

The root cause is classified as CWE-190 (Integer Overflow or Wraparound). The zchunk library performs addition operations on data size values (comp->data_size + src_size and comp->dc_data_size + src_size) without first validating that the result will not exceed the maximum representable value. When the sum exceeds the integer boundary, it wraps around to a small value, causing zrealloc() to allocate insufficient memory.

Attack Vector

The attack requires local access and user interaction. An attacker crafts a malicious zchunk file with specifically chosen size values in the file headers or chunk metadata. When a vulnerable application processes this file:

1. The library reads the malicious size values from the file
2. Size calculations overflow, resulting in a small allocation size
3. The library allocates an undersized buffer via zrealloc()
4. Subsequent write operations overflow the buffer
5. The attacker achieves memory corruption, potentially leading to code execution

// Vulnerable code pattern in src/lib/comp/comp.c (before patch)
// The addition could overflow, causing undersized allocation
comp->data = zrealloc(comp->data, comp->data_size + src_size);

// Security patch adds overflow detection:
if((comp->data_size > comp->data_size + src_size) ||
   (src_size > comp->data_size + src_size)) {
    zck_log(ZCK_LOG_ERROR, "Integer overflow when reading data");
    return false;
}

comp->data = zrealloc(comp->data, comp->data_size + src_size);

Source: GitHub Commit for zchunk

Detection Methods for CVE-2023-46228

Indicators of Compromise

• Unexpected crashes or segmentation faults in applications processing zchunk files
• Abnormal memory allocation patterns or out-of-memory errors when handling small zchunk files
• Core dumps from zchunk-dependent applications showing heap corruption

Detection Strategies

• Monitor for abnormal behavior in applications using zchunk library during file processing operations
• Implement file integrity monitoring for zchunk files entering the system through downloads or file transfers
• Use memory sanitizers (AddressSanitizer, Valgrind) in development and testing environments to detect heap overflows
• Deploy endpoint protection that can detect heap corruption exploitation attempts

Monitoring Recommendations

• Enable application crash reporting and analyze core dumps for signs of memory corruption in zchunk-related processes
• Monitor system logs for applications that process zchunk files exhibiting unusual behavior
• Track file operations involving .zck file extensions from untrusted sources

How to Mitigate CVE-2023-46228

Immediate Actions Required

• Upgrade zchunk to version 1.3.2 or later immediately
• Audit systems to identify all instances of the vulnerable zchunk library
• Restrict processing of zchunk files from untrusted sources until patches are applied
• Update Linux distribution packages that depend on zchunk

Patch Information

The vulnerability has been fixed in zchunk version 1.3.2. The patch adds explicit integer overflow checks before performing memory allocations in the affected functions. The security fix is available in commit 08aec2b4dfd7f709b6e3d511411ffcc83ed4efbe.

For detailed information, refer to:

• SUSE Bug Report #1216268
• GitHub Commit for zchunk
• GitHub zchunk Version Comparison

Workarounds

• If immediate patching is not possible, restrict access to zchunk file processing functionality
• Implement input validation at the application level to reject suspiciously large size values in zchunk files
• Use sandboxing or containerization for applications that must process untrusted zchunk files

# Check installed zchunk version on Linux systems
rpm -qa | grep zchunk
# or
dpkg -l | grep zchunk

# Update zchunk package (Fedora/RHEL/CentOS)
sudo dnf update zchunk

# Update zchunk package (Debian/Ubuntu)
sudo apt update && sudo apt upgrade libzck*