CVE-2025-70103

Executive Summary

CVE-2025-70103 is a critical heap buffer overflow vulnerability discovered in libjxl version 0.12.0. The flaw resides in the jxl::extras::DecodeImagePNM function within lib/extras/dec/pnm.cc, which is responsible for decoding PBM (Portable Bitmap) images. An attacker can exploit this vulnerability by crafting a malicious PBM image that, when processed by the vulnerable function, causes a heap buffer overflow. This can lead to memory corruption, potentially enabling arbitrary code execution or denial of service. The vulnerability has a CVSS score of 0.0 in the NVD, but this is likely a placeholder; the actual severity is high due to the nature of heap overflows. No public proof-of-concept (PoC) or exploit code is available at this time, and the patch status remains unknown.

Supply Chain & Package Security

libjxl is a C++ library for JPEG XL image encoding/decoding, used in various applications and libraries. The vulnerability affects the library itself, not a specific package manager ecosystem (NPM, PyPI, Go, Ruby). However, any application or service that uses libjxl 0.12.0 to process PBM images is at risk. Users should monitor for updates from the libjxl project and consider alternative image processing libraries if a patch is not forthcoming.

CVSS Breakdown & Threat Level

The official CVSS score is 0.0, which is likely a placeholder or error. Based on the vulnerability type (heap buffer overflow) and the potential impact, a more realistic assessment is:

• Attack Vector (AV): Local (L) – requires the attacker to provide a malicious PBM file.
• Attack Complexity (AC): Low (L) – no special conditions needed.
• Privileges Required (PR): None (N) – no authentication needed.
• User Interaction (UI): Required (R) – victim must open the file.
• Scope (S): Unchanged (U) – vulnerability does not cross trust boundaries.
• Confidentiality (C): High (H) – potential for memory leak.
• Integrity (I): High (H) – potential for code injection.
• Availability (A): High (H) – potential for crash.

Estimated CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Estimated Score: 7.8 (High)

Threat Level: High – due to the potential for remote code execution via a crafted image file.

Deep Dive & Mechanics

The vulnerability is a classic heap buffer overflow in the PBM decoder. The DecodeImagePNM function reads PBM image data and allocates a buffer on the heap to store pixel data. The flaw occurs when the function does not properly validate the dimensions or data size specified in the PBM header. An attacker can craft a PBM file with a header that declares a small image size but contains a larger amount of pixel data, or vice versa, causing the function to write beyond the allocated buffer.

Root Cause: Insufficient bounds checking in the PBM parsing logic. The function likely calculates the buffer size based on the width and height from the header but does not verify that the actual data read matches the expected size. This allows an attacker to overflow the heap buffer with controlled data.

Impact: A successful exploit can corrupt adjacent heap memory, potentially leading to arbitrary code execution, data corruption, or a denial of service (crash). The attacker controls the overflow data, making code execution possible if heap layout can be manipulated.

Vulnerable vs. Patched Code

Since no patch is available, we can only describe the vulnerable code pattern. The vulnerable function in lib/extras/dec/pnm.cc likely contains code similar to:

// Vulnerable code (conceptual)
bool DecodeImagePNM(const uint8_t* data, size_t size, Image* image) {
  // Parse header to get width, height, max_val
  size_t width = ...;
  size_t height = ...;
  size_t pixel_size = ...; // e.g., 1 for PBM
  size_t buffer_size = width * height * pixel_size;
  uint8_t* buffer = new uint8_t[buffer_size];
  // Read pixel data directly into buffer without checking bounds
  for (size_t i = 0; i < size; i++) {
    buffer[i] = data[i]; // Potential overflow if data size > buffer_size
  }
  // ...
}

A patched version would include a check:

// Patched code (conceptual)
bool DecodeImagePNM(const uint8_t* data, size_t size, Image* image) {
  size_t width = ...;
  size_t height = ...;
  size_t pixel_size = ...;
  size_t buffer_size = width * height * pixel_size;
  if (size < buffer_size) {
    // Error: not enough data
    return false;
  }
  uint8_t* buffer = new uint8_t[buffer_size];
  // Only copy the expected amount
  memcpy(buffer, data, buffer_size);
  // ...
}

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• libjxl 0.12.0 installed on a target system.
• Ability to deliver a malicious PBM file to the target (e.g., via email, web download, or file upload).

Exploitation Steps:

1. Craft a Malicious PBM File: Create a PBM file with a header that declares a small image (e.g., 10x10 pixels) but contains a large amount of pixel data (e.g., 10000 bytes). The overflow data should be crafted to overwrite heap metadata or function pointers.
2. Deliver the File: Send the file to the target via phishing, file upload, or other means.
3. Trigger the Vulnerability: The target opens the file using an application that relies on libjxl 0.12.0 (e.g., an image viewer or converter).
4. Achieve Code Execution: If the heap layout is predictable, the overflow can overwrite a function pointer or return address, leading to arbitrary code execution.

Lab Setup:

• Use a virtual machine with a vulnerable version of libjxl (0.12.0).
• Compile a simple test program that calls DecodeImagePNM with the malicious file.
• Use a debugger (e.g., GDB) to observe the overflow and control flow.

Example Malicious PBM File (Hex):

50 34 0A 31 30 20 31 30 0A 31 0A  // P4 header: width=10, height=10, max_val=1
[10000 bytes of overflow data]      // Actual data exceeds buffer

Blue Team (Defense)

Detection:

• Monitor for crashes in applications using libjxl.
• Use memory corruption detection tools (e.g., AddressSanitizer) during development.
• Implement file validation before processing: check that the PBM file's data size matches the header.

Mitigation:

• Disable PBM support in libjxl if not needed.
• Use a sandboxed environment for image processing.
• Apply ASLR and DEP to mitigate exploitation.

Indicators of Compromise (IOCs)

• File Hashes: (None available, but any PBM file that triggers the overflow will have a mismatch between header dimensions and actual data size.)
• Network Traffic: Unusual PBM file transfers (e.g., large files with small headers).
• System Logs: Application crashes with heap corruption errors (e.g., "heap buffer overflow" in debug logs).
• Memory Artifacts: Corrupted heap metadata or unexpected code execution in the libjxl process.

Detection Engineering

YARA Rule

rule CVE_2025_70103_PBM_Overflow {
  meta:
    description = "Detects malicious PBM files exploiting CVE-2025-70103"
    author = "Valters IT"
    date = "2025-04-10"
    hash = "unknown"
  strings:
    $p4_header = { 50 34 0A } // "P4\n"
    $p1_header = { 50 31 0A } // "P1\n"
  condition:
    ($p4_header or $p1_header) and
    // Check for mismatch between header dimensions and file size
    // This is a simplified heuristic; actual detection requires parsing
    filesize > 1000000 // Example: file larger than 1MB
}

Sigma Rule

title: CVE-2025-70103 Heap Buffer Overflow in libjxl PBM Decoder
id: cve-2025-70103
status: experimental
description: Detects potential exploitation attempts via crafted PBM files
logsource:
  category: process_creation
  product: windows
detection:
  selection:
    Image|endswith: '\libjxl.dll'
    CommandLine|contains: 'pbm'
  condition: selection
falsepositives:
  - Legitimate PBM file processing
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-70103 - Malicious PBM File Transfer"; flow:to_client; file.data; content:"P4"; within:2; file.size:>1000000; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable PBM Support: If possible, disable the PBM decoder in libjxl by removing or patching the DecodeImagePNM function.
2. Update libjxl: Monitor the libjxl project for a patched version (e.g., 0.12.1 or later). Apply the update as soon as it becomes available.
3. Input Validation: Implement strict validation of PBM file headers and data sizes before processing.

Long-Term Measures:

• Use memory-safe languages or libraries for image processing.
• Employ fuzzing to discover similar vulnerabilities.
• Enable compiler hardening flags (e.g., -fstack-protector-strong, -D_FORTIFY_SOURCE=2).

Workarounds:

• Convert PBM files to a safer format (e.g., PNG) before processing with libjxl.
• Use a different image processing library that does not have this vulnerability.

Valters IT
DevSecOps & Cyber Threat Intelligence Expert