CVE-2026-27799: ImageMagick Buffer Overflow Vulnerability

CVE-2026-27799 Overview

A heap buffer over-read vulnerability has been discovered in ImageMagick, the widely-used open-source software suite for image editing and manipulation. The vulnerability exists in the DJVU image format handler and occurs due to integer truncation when calculating the stride (row size) for pixel buffer allocation. When processing specially crafted DJVU images, the stride calculation overflows a 32-bit signed integer, resulting in out-of-bounds memory reads.

Critical Impact

Attackers can exploit this vulnerability through malicious DJVU image files to trigger out-of-bounds memory reads, potentially leading to information disclosure or application crashes.

Affected Products

• ImageMagick versions prior to 7.1.2-15
• ImageMagick versions prior to 6.9.13-40
• Magick.NET versions prior to 14.10.3

Discovery Timeline

• 2026-02-26 - CVE CVE-2026-27799 published to NVD
• 2026-02-26 - Last updated in NVD database

Technical Details for CVE-2026-27799

Vulnerability Analysis

This vulnerability is classified as CWE-122 (Heap-based Buffer Overflow), specifically manifesting as an out-of-bounds read condition. The issue stems from improper integer type handling in the DJVU image decoder within coders/djvu.c. When ImageMagick processes a DJVU file, it calculates the stride value to determine row sizes for pixel buffer allocation. The use of a signed 32-bit integer (int) for the stride variable creates conditions where large image dimensions can cause integer truncation, leading to undersized buffer allocations and subsequent out-of-bounds memory access.

The vulnerability requires local access and involves high attack complexity, as the attacker must deliver a specially crafted DJVU file to the target system and have ImageMagick process it. While no user interaction is required once the file is processed, the attack does not allow for scope change beyond the vulnerable component.

Root Cause

The root cause is the use of an incorrectly sized integer type for the stride variable in the DJVU decoder. The stride calculation, which determines the byte width of each image row, was stored in a signed 32-bit integer (int). For large image dimensions, this calculation can overflow the 32-bit signed integer limit, causing integer truncation. The truncated value then leads to insufficient memory allocation for the pixel buffer, resulting in heap buffer over-reads when the decoder attempts to access pixel data beyond the allocated boundary.

Attack Vector

Exploitation requires local access to deliver a malicious DJVU image file to a system running vulnerable versions of ImageMagick. The attack vector involves:

1. Crafting a DJVU file with dimensions calculated to trigger integer truncation in the stride calculation
2. Having the target system process the malicious file through ImageMagick (via command-line tools, web applications, or library integrations)
3. The integer overflow causes an undersized buffer allocation
4. Subsequent read operations access memory beyond the allocated buffer boundaries

The following patch from the ImageMagick GitHub commit corrects the vulnerability by changing the stride variable from a signed 32-bit integer to an unsigned size_t:

   Image
     *image;
 
-  int
+  size_t
     stride;
 
   unsigned char

Source: https://github.com/ImageMagick/ImageMagick/commit/e87695b3227978ad70b967b8d054baaf8ac2cced

Detection Methods for CVE-2026-27799

Indicators of Compromise

• Unexpected crashes or segmentation faults when ImageMagick processes DJVU files
• Abnormal memory access patterns in ImageMagick processes
• Error logs indicating buffer overflows or memory corruption in DJVU handling
• Unusual DJVU files with extremely large or suspicious dimension values

Detection Strategies

• Monitor ImageMagick process crashes and analyze crash dumps for indicators of heap corruption
• Implement file inspection rules to detect DJVU files with abnormal header values or dimension specifications
• Deploy memory sanitization tools (AddressSanitizer, Valgrind) in development and testing environments to catch out-of-bounds reads
• Use application-level logging to track DJVU file processing operations

Monitoring Recommendations

• Enable verbose logging for ImageMagick operations to capture processing errors
• Monitor system logs for repeated crashes of ImageMagick-related processes
• Implement file upload scanning for applications that accept user-provided images
• Track resource utilization anomalies that may indicate exploitation attempts

How to Mitigate CVE-2026-27799

Immediate Actions Required

• Upgrade ImageMagick to version 7.1.2-15 or later (for 7.x branch)
• Upgrade ImageMagick to version 6.9.13-40 or later (for 6.x branch)
• Upgrade Magick.NET to version 14.10.3 or later if using the .NET wrapper
• Audit systems and applications for vulnerable ImageMagick installations

Patch Information

The vulnerability has been patched in ImageMagick versions 7.1.2-15 and 6.9.13-40. The fix changes the stride variable type from int to size_t in the DJVU decoder, preventing integer truncation during stride calculations.

Patch resources:

• ImageMagick Security Advisory (GHSA-r99p-5442-q2x2)
• GitHub Commit with Fix
• Magick.NET Release 14.10.3

Workarounds

• Disable DJVU format processing by adding DJVU to the ImageMagick policy.xml deny list
• Implement strict input validation for image dimensions before processing
• Use sandboxing or containerization to isolate ImageMagick processing operations
• Restrict ImageMagick to process only trusted image sources

<!-- Add to ImageMagick policy.xml to disable DJVU processing -->
<policymap>
  <policy domain="coder" rights="none" pattern="DJVU" />
</policymap>