CVE-2023-51607

Executive Summary

CVE-2023-51607 is a low-severity (CVSS 3.3) information disclosure vulnerability in Kofax Power PDF. The flaw resides in the parsing of PNG files, where an out-of-bounds read can occur due to insufficient validation of user-supplied data. Exploitation requires user interaction (opening a malicious file or visiting a malicious page). While the direct impact is limited to information disclosure, an attacker could chain this vulnerability with other flaws to achieve arbitrary code execution. No public proof-of-concept (PoC) or exploit code is currently available, and the vendor has not released a patch.

Supply Chain & Package Security

This vulnerability is not related to any open-source package ecosystem (NPM, PyPI, Go, Ruby). It affects a proprietary desktop application (Kofax Power PDF). Supply chain risks are limited to the distribution of malicious PDF files containing crafted PNG images.

CVSS Breakdown & Threat Level

• CVSS Score: 3.3 (Low)
• Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N
• Attack Vector (AV): Local (requires user to open a file)
• Attack Complexity (AC): Low
• Privileges Required (PR): None
• User Interaction (UI): Required (victim must open the malicious file)
• Scope (S): Unchanged
• Confidentiality (C): Low (limited memory disclosure)
• Integrity (I): None
• Availability (A): None

Threat Level: Low. The vulnerability is difficult to exploit for significant impact without chaining. The EPSS score of 0.0% indicates extremely low exploitation activity in the wild.

Deep Dive & Mechanics

The vulnerability is an out-of-bounds read (CWE-125) in the PNG parsing module of Kofax Power PDF. When the application processes a specially crafted PNG file embedded within a PDF, it fails to properly validate the length of user-supplied data before reading from an allocated buffer. This results in reading memory beyond the intended boundary.

Technical Details:

• The flaw is triggered during the parsing of PNG chunk data (e.g., IDAT, IHDR, or custom chunks).
• The application reads a length field from the PNG chunk but does not verify that the chunk data fits within the allocated buffer.
• An attacker can craft a PNG with a manipulated length field, causing the parser to read past the end of the buffer.
• This read can leak sensitive information from adjacent memory, such as other document data, system addresses, or credentials.

Chaining Potential: While the direct impact is information disclosure, an attacker could combine this with a separate memory corruption vulnerability (e.g., heap overflow) to achieve arbitrary code execution. The ZDI advisory (ZDI-CAN-21829) notes this possibility.

Vulnerable vs. Patched Code

Since no patch is available, a direct code comparison is not possible. However, the vulnerable code pattern is typical of C/C++ applications parsing binary formats:

Vulnerable Code (Conceptual):

void parse_png_chunk(char *buffer, size_t buffer_size) {
    uint32_t chunk_length = read_uint32(buffer); // No validation
    char *chunk_data = buffer + 8; // Skip length and type
    // Out-of-bounds read if chunk_length > buffer_size - 8
    process_chunk(chunk_data, chunk_length);
}

Patched Code (Expected):

void parse_png_chunk(char *buffer, size_t buffer_size) {
    uint32_t chunk_length = read_uint32(buffer);
    if (chunk_length > buffer_size - 8) {
        // Handle error: invalid chunk length
        return;
    }
    char *chunk_data = buffer + 8;
    process_chunk(chunk_data, chunk_length);
}

Exploitation & Lab Setup

Red Team

Prerequisites:

• Kofax Power PDF (any version)
• A PDF file with an embedded malicious PNG

Steps:

1. Craft a PNG file with a manipulated chunk length field (e.g., set IDAT chunk length to a value larger than the actual data).
2. Embed the PNG into a PDF using a tool like pdf-parser.py or a hex editor.
3. Host the PDF on a web server or send it via email.
4. When the victim opens the PDF in Kofax Power PDF, the out-of-bounds read occurs, potentially leaking memory contents.

Note: No public exploit code is available. This is a conceptual approach.

Blue Team

Detection:

• Monitor for unusual PDF files with embedded PNGs that have anomalous chunk sizes.
• Use the YARA and Sigma rules provided in the Detection Engineering section.
• Enable application whitelisting to prevent execution of untrusted PDFs.

Hunting:

• Search for Kofax Power PDF crashes or hangs that may indicate exploitation attempts.
• Analyze memory dumps for signs of out-of-bounds reads (e.g., repeated patterns in adjacent memory).

Indicators of Compromise (IOCs)

• File Hashes: No specific hashes available.
• Network Indicators: No network indicators; exploitation is local.
• Behavioral:
  • Kofax Power PDF process (PowerPDF.exe) reading beyond allocated memory.
  • Unexpected memory access patterns in the PNG parsing module.
  • Application crashes with access violation errors.

Detection Engineering

YARA Rule

rule CVE_2023_51607_PNG_OOB_Read {
    meta:
        description = "Detects malicious PNG files exploiting CVE-2023-51607 in Kofax Power PDF"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2023-51607"
    strings:
        $png_header = { 89 50 4E 47 0D 0A 1A 0A } // PNG magic bytes
        $chunk_length_anomaly = /.{4}(?=[\x00-\x08])/ // Chunk length > 8 bytes but less than 9 (anomalous)
    condition:
        $png_header at 0 and #chunk_length_anomaly > 0
}

Sigma Rule

title: CVE-2023-51607 Kofax Power PDF PNG OOB Read
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects potential exploitation of CVE-2023-51607 via anomalous PNG chunk sizes in PDF files
author: Valters IT
logsource:
    category: file_event
    product: windows
detection:
    selection:
        Image|endswith: '\PowerPDF.exe'
        TargetFilename|endswith: '.pdf'
    condition: selection
falsepositives:
    - Legitimate PDFs with unusual PNG chunks
level: low

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2023-51607 Kofax Power PDF PNG OOB Read Attempt"; flow:to_server,established; content:"|89 50 4E 47 0D 0A 1A 0A|"; depth:8; content:"|00 00 00 00|"; distance:8; within:4; byte_test:4,>,0,0,relative; classtype:attempted-recon; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. No patch available. Contact Kofax support for updates.
2. User Awareness: Train users not to open PDF files from untrusted sources.
3. Application Control: Use AppLocker or similar to restrict execution of Kofax Power PDF to trusted scenarios.

Long-term:

• Monitor vendor advisories for a patch.
• Consider using alternative PDF readers with more robust parsing (e.g., Adobe Acrobat, Foxit Reader) until a fix is released.
• Implement memory protection mechanisms (ASLR, DEP) on endpoints.

Workaround:

• Disable automatic rendering of embedded images in Kofax Power PDF settings (if available).

Valters IT
DevSecOps & Cyber Threat Intelligence