CVE-2026-23876: ImageMagick Buffer Overflow Vulnerability

CVE-2026-23876 Overview

ImageMagick is open-source software for editing and manipulating digital images. A heap buffer overflow vulnerability exists in the XBM image decoder function ReadXBMImage. The flaw allows attackers to write controlled data past an allocated heap buffer when processing a crafted XBM file. Any operation that reads or identifies an image can trigger the overflow. This makes the vulnerability exploitable through common image upload and processing pipelines used by web applications, content management systems, and document conversion services. Versions 7.1.2-13 and 6.9.13-38 resolve the issue.

Critical Impact
Remote attackers can achieve heap corruption and potential code execution by uploading a malicious XBM file to any service that processes images with vulnerable ImageMagick versions.

Affected Products

ImageMagick versions prior to 7.1.2-13
ImageMagick versions prior to 6.9.13-38
Applications and services embedding vulnerable ImageMagick libraries for image identification or processing

Discovery Timeline

2026-01-20 - CVE-2026-23876 published to the National Vulnerability Database (NVD)
2026-01-29 - Last updated in NVD database

Technical Details for CVE-2026-23876

Vulnerability Analysis

The vulnerability is a heap buffer overflow [CWE-122] in the ReadXBMImage function, which parses X BitMap (XBM) image files. When ImageMagick decodes a maliciously crafted XBM file, the decoder writes attacker-controlled bytes beyond the bounds of the heap buffer allocated for pixel data. Heap corruption of this type can be leveraged to overwrite adjacent allocator metadata or function pointers, leading to remote code execution under the privileges of the image-processing service.

XBM is a plain-text C-source-like bitmap format. Parsers typically read dimensions from header tokens and allocate a buffer sized from those dimensions before reading hex byte arrays into it. Mismatches between declared and actual data, or arithmetic errors when computing buffer size, are the recurring root cause of overflows in such decoders.

Root Cause

The root cause is improper bounds enforcement during the read loop in ReadXBMImage. The decoder trusts size-related values derived from the input file when writing decoded data into the heap allocation. Consult the GitHub Security Advisory GHSA-r49w-jqq3-3gx8 and the upstream fix commit for the precise code-level details.

Attack Vector

Exploitation requires no authentication and no user interaction beyond submitting an image. An attacker uploads a crafted XBM file to any endpoint that calls convert, identify, mogrify, or library bindings such as Imagick, MagickWand, or RMagick. Server-side thumbnailing, avatar processing, OCR pre-processing, and PDF-to-image pipelines are all viable delivery surfaces. The vulnerability has an EPSS score of 0.088% (25th percentile) as of 2026-05-14.

The vulnerability manifests in the XBM decoder's write loop. No verified public proof-of-concept code is available at the time of writing. Refer to the upstream advisory for technical reproduction details.

Detection Methods for CVE-2026-23876

Indicators of Compromise

Crashes or abnormal terminations of convert, identify, magick, or host application processes when handling XBM input
Unexpected child processes spawned by image-processing workers, particularly shells or network utilities
Inbound HTTP requests delivering files with .xbm extensions or image/x-xbitmap content type to upload endpoints
Heap corruption signatures in core dumps referencing ReadXBMImage in the call stack

Detection Strategies

Inventory installed ImageMagick versions across servers and container images and flag any below 7.1.2-13 or 6.9.13-38
Inspect web application logs for uploads of XBM files, an uncommon format in production traffic
Enable AddressSanitizer or similar instrumentation in pre-production builds to surface heap overflows during fuzz testing
Correlate image-worker crashes with preceding upload events through centralized logging

Monitoring Recommendations

Alert on segmentation faults or SIGABRT events originating from ImageMagick binaries
Monitor process trees for unexpected children of image-processing services, such as sh, bash, curl, or wget
Track outbound network connections from image-processing hosts that previously had no egress baseline
Audit policy.xml to confirm restrictive coder policies are enforced and not silently overridden

How to Mitigate CVE-2026-23876

Immediate Actions Required

Upgrade ImageMagick to 7.1.2-13 or 6.9.13-38 or later across all systems and container images
Rebuild and redeploy applications that statically link or bundle ImageMagick libraries
Restrict the XBM coder in ImageMagick policy.xml until patching is complete
Validate uploaded image MIME types and reject unexpected formats at the application layer

Patch Information

The upstream fix is committed in ImageMagick commit 2fae241 and released in versions 7.1.2-13 and 6.9.13-38. Linux distributions are publishing backported packages. Verify your package manager reports a fixed version before declaring remediation complete.

Workarounds

Disable the XBM coder via policy.xml to block decoding entirely until patches are applied
Sandbox image-processing workers using seccomp, AppArmor, or container isolation to limit blast radius
Run image processing in short-lived, unprivileged containers without outbound network access
Enforce strict allow-lists of accepted image formats at the application gateway

bash

# Disable the XBM coder in ImageMagick policy.xml
# Add the following inside the <policymap> element:
#   <policy domain="coder" rights="none" pattern="XBM" />

sudo sed -i 's|</policymap>|  <policy domain="coder" rights="none" pattern="XBM" />\n</policymap>|' /etc/ImageMagick-7/policy.xml

# Verify the policy is active
identify -list policy | grep -i xbm