CVE-2025-53367: DjVuLibre Buffer Overflow Vulnerability

CVE-2025-53367 Overview

CVE-2025-53367 is an out-of-bounds write vulnerability affecting DjVuLibre, a GPL implementation of DjVu, a web-centric format for distributing documents and images. The vulnerability exists in the MMRDecoder::scanruns method, which fails to validate that the xr pointer remains within the bounds of the allocated buffer. This oversight enables writes beyond allocated memory, leading to heap corruption. Additionally, an out-of-bounds read condition with the pr pointer is also possible due to the same missing boundary checks.

Successful exploitation of this vulnerability could allow an attacker to corrupt heap memory, potentially leading to arbitrary code execution or application crashes when a user opens a maliciously crafted DjVu file.

Critical Impact

Heap corruption through out-of-bounds write can enable arbitrary code execution when processing malicious DjVu documents, requiring user interaction to open the file.

Affected Products

• DjVuLibre versions prior to 3.5.29
• Applications and document viewers that incorporate DjVuLibre for DjVu file processing
• Linux distributions packaging vulnerable DjVuLibre versions (including Debian)

Discovery Timeline

• 2025-07-03 - CVE-2025-53367 published to NVD
• 2025-11-04 - Last updated in NVD database

Technical Details for CVE-2025-53367

Vulnerability Analysis

The vulnerability resides in the MMRDecoder::scanruns method within DjVuLibre's image decoding functionality. The core issue stems from improper bounds checking when processing encoded data streams. During the decoding process, the method uses pointer arithmetic to traverse and write to a buffer. However, the implementation fails to verify that the xr pointer does not exceed the buffer's allocated boundaries before performing write operations.

This missing validation creates a classic out-of-bounds write condition. When processing specially crafted DjVu files, an attacker can manipulate the encoded data to cause the xr pointer to extend beyond the allocated buffer, resulting in heap memory corruption. The same lack of bounds checking affects the pr pointer, introducing a secondary out-of-bounds read vulnerability.

The exploitation requires user interaction, as the victim must open a malicious DjVu file. Document viewers, image processing applications, and any software utilizing DjVuLibre for DjVu file handling are potentially affected.

Root Cause

The root cause is insufficient input validation and missing boundary checks in the MMRDecoder::scanruns method. The function does not verify that pointer operations remain within the allocated memory region before writing decoded data. This allows maliciously crafted input to direct writes to arbitrary heap locations, bypassing expected memory boundaries.

The vulnerability is classified under CWE-125 (Out-of-bounds Read), though the primary security impact stems from the out-of-bounds write capability which enables heap corruption.

Attack Vector

The attack vector requires local access with user interaction. An attacker must craft a malicious DjVu document containing specially structured encoded data that triggers the out-of-bounds condition during the MMR decoding process. The attack flow is as follows:

1. Attacker creates a malicious DjVu file with crafted MMR-encoded content designed to manipulate pointer arithmetic
2. The victim opens the malicious file using an application that relies on DjVuLibre for rendering
3. During file processing, the MMRDecoder::scanruns method processes the malicious data
4. The xr pointer exceeds buffer boundaries and writes attacker-controlled data to the heap
5. Heap corruption occurs, potentially enabling code execution or causing application crash

The vulnerability affects document processing workflows where untrusted DjVu files might be opened, including document management systems, image viewers, and conversion utilities.

Detection Methods for CVE-2025-53367

Indicators of Compromise

• Unexpected crashes in applications using DjVuLibre when opening DjVu files
• Memory corruption errors or heap-related exceptions in processes handling DjVu documents
• Abnormal memory allocation patterns in applications processing DjVu files
• Unusual file access patterns involving .djvu or .djv file extensions from untrusted sources

Detection Strategies

• Monitor for crashes and segmentation faults in DjVuLibre-dependent applications with stack traces pointing to MMRDecoder::scanruns
• Implement file type validation and sandboxed processing for DjVu documents from external sources
• Deploy endpoint detection to identify exploitation attempts through malicious document delivery
• Enable AddressSanitizer (ASan) in development and testing environments to detect heap corruption

Monitoring Recommendations

• Log and alert on repeated DjVuLibre-related crashes across endpoints
• Monitor email attachments and web downloads for DjVu file types from untrusted sources
• Track version information of DjVuLibre installations across the environment to identify unpatched systems
• Implement behavioral analysis for document processing applications to detect anomalous memory operations

How to Mitigate CVE-2025-53367

Immediate Actions Required

• Upgrade DjVuLibre to version 3.5.29 or later which contains the security patch
• Apply available operating system security updates, particularly for Debian-based systems which have issued patches
• Consider temporarily blocking or quarantining DjVu files from untrusted sources until patching is complete
• Audit applications and dependencies that utilize DjVuLibre and prioritize updates

Patch Information

The vulnerability has been patched in DjVuLibre version 3.5.29. The fix implements proper boundary validation for the xr and pr pointers in the MMRDecoder::scanruns method to prevent out-of-bounds memory access.

The patch commit is available at the SourceForge commit reference. Linux distribution users should apply updates through their package managers:

• Debian LTS users should refer to the Debian LTS Announcement
• Additional technical details are available in the GitHub Security Advisory

Workarounds

• Restrict DjVu file processing to sandboxed environments until patching is completed
• Implement strict file type filtering to block DjVu files at email gateways and web proxies
• Disable or remove DjVuLibre-dependent applications from systems that do not require DjVu functionality
• Use application-level sandboxing technologies to limit the impact of potential exploitation

# Check installed DjVuLibre version
djvused --version

# Update DjVuLibre on Debian/Ubuntu systems
sudo apt update && sudo apt upgrade djvulibre-bin libdjvulibre21

# Verify the updated version is 3.5.29 or later
dpkg -l | grep djvulibre