CVE-2026-56373: ImageMagick Use-After-Free Vulnerability

CVE-2026-56373 Overview

CVE-2026-56373 is a use-after-free vulnerability [CWE-416] in ImageMagick versions before 7.1.2-15. The flaw resides in the Palm Database (PDB) image decoder, which uses a stale pointer when a memory allocation fails during image processing. Attackers can trigger the condition by supplying a crafted PDB file to any application or service that decodes images with ImageMagick. Successful exploitation causes a crash or writes a single zero byte to freed memory, producing a denial-of-service condition and potentially corrupting adjacent heap state.

Critical Impact
Processing an attacker-supplied PDB file with a vulnerable ImageMagick build can crash the host process or write a zero byte into freed heap memory, enabling denial of service across web pipelines, thumbnail generators, and document conversion services.

Affected Products

ImageMagick versions prior to 7.1.2-15
Applications and services that embed ImageMagick libraries (MagickCore, MagickWand) for PDB decoding
Server-side image processing pipelines (upload handlers, thumbnailers, converters) using vulnerable ImageMagick builds

Discovery Timeline

2026-07-10 - CVE-2026-56373 published to NVD
2026-07-13 - Last updated in NVD database

Technical Details for CVE-2026-56373

Vulnerability Analysis

The vulnerability exists in the PDB coder module of ImageMagick, responsible for parsing Palm Database image files. During decoding, the routine allocates memory for pixel or scanline buffers derived from attacker-controlled fields in the PDB header. When an allocation fails and returns NULL, the decoder does not correctly reset or abandon the pointer it had previously referenced. Subsequent cleanup or write operations then dereference the stale pointer, producing a use-after-free condition [CWE-416]. The observable effect is either an immediate crash or a single zero-byte write into memory that has already been freed, which may corrupt allocator metadata or adjacent objects.

Root Cause

The root cause is improper error handling in the PDB decoder path. When the allocator fails, the code retains a reference to memory that has been released, then either writes to it or passes it to a downstream free routine. Because PDB header fields such as width, height, and compressed size are attacker-controlled, adversaries can reliably drive allocations into failure conditions on systems with constrained memory or resource limits.

Attack Vector

Exploitation is network-reachable when ImageMagick is exposed indirectly through a web application, API, or file-conversion service. The attacker uploads or submits a malformed PDB file, and the vulnerable process performs the decode. No authentication or user interaction is required beyond the normal file submission workflow. Attack complexity is high because the attacker must shape allocation state so that the targeted allocation fails at the right time. Impact is limited to availability; the advisory does not describe confidentiality or integrity loss.

No public proof-of-concept is currently listed for CVE-2026-56373. Technical particulars are documented in the ImageMagick GitHub Security Advisory GHSA-3j4x-rwrx-xxj9 and the VulnCheck advisory.

Detection Methods for CVE-2026-56373

Indicators of Compromise

Unexpected termination or SIGSEGV crashes in convert, magick, identify, or host processes linking libMagickCore when handling uploaded images.
Presence of .pdb files or files with PDB magic bytes in image upload directories where such formats are not expected.
Heap corruption or glibc abort messages such as double free or corruption and free(): invalid pointer in application logs following image processing.

Detection Strategies

Inventory installed ImageMagick versions across servers and containers, flagging any build older than 7.1.2-15.
Enable ImageMagick policy logging and correlate PDB decode events with process crashes or worker restarts.
Run vulnerable candidates against fuzz corpora or the reproducer referenced in the vendor advisory in a controlled environment to confirm exposure.

Monitoring Recommendations

Monitor image-processing worker processes for abnormal exit codes, OOM kills, and restart storms indicative of repeated decode failures.
Alert on submission of PDB-format files to endpoints that only expect common formats such as JPEG, PNG, or WebP.
Track memory allocator diagnostics (MALLOC_CHECK_, ASan output in non-production builds) to surface use-after-free signatures early.

How to Mitigate CVE-2026-56373

Immediate Actions Required

Upgrade ImageMagick to version 7.1.2-15 or later on every host, container image, and build pipeline that includes the library.
Disable the PDB coder in policy.xml where the format is not required, using a rights="none" pattern for PDB.
Restrict which file formats server-side pipelines will accept before invoking ImageMagick, rejecting PDB inputs at the application layer.

Patch Information

The ImageMagick project addressed CVE-2026-56373 in release 7.1.2-15. Refer to the ImageMagick GitHub Security Advisory GHSA-3j4x-rwrx-xxj9 for the fix commit and affected version ranges. Rebuild any distribution package, container image, or bundled application that statically links against libMagickCore to inherit the fix.

Workarounds

Add a policy entry that blocks the PDB decoder until patching is complete.
Run image processing in isolated, resource-limited workers (containers or sandboxes) so that a crash does not affect the parent service.
Enforce strict MIME and magic-byte allowlists at the ingest layer to prevent PDB files from reaching the decoder.

bash

# Configuration example: disable the PDB coder in ImageMagick policy.xml
# File location: /etc/ImageMagick-7/policy.xml (path varies by distro)
<policymap>
  <policy domain="coder" rights="none" pattern="PDB" />
</policymap>

# Verify installed version meets the fix
magick -version | head -n 1
# Expect: Version: ImageMagick 7.1.2-15 or later