CVE-2026-86421 in ImageMagick
Summary
by MITRE • 09/07/2026
ImageMagick before 7.1.2-30 and 6.9.13-55 contains a memory leak in the MSL image decoder. A crafted MSL image triggers memory allocation without proper deallocation, allowing an attacker to exhaust memory and cause a denial of service.
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Analysis
by VulDB Data Team • 09/08/2026
The vulnerability identified in ImageMagick versions prior to 7.1.2-30 and 6.9.13-55 represents a critical resource management flaw within the Markupup Script Language, or MSL, image decoder subsystem. This component is responsible for parsing XML-based instructions that define how images are processed, composited, and rendered. The core technical deficiency lies in the handling of memory allocation routines during the decoding process. Specifically, when processing a specially crafted MSL document, the application fails to properly release allocated memory buffers after they have served their immediate purpose or upon encountering certain parsing states. This oversight results in a progressive accumulation of unreleased heap memory with each processed instruction block that triggers this specific code path. The flaw is not related to buffer overflows or arbitrary code execution but rather stems from an incomplete cleanup routine within the parser logic, which neglects to invoke deallocation functions for dynamically allocated structures associated with MSL elements such as images, masks, or transformations.
From a technical perspective, this issue aligns closely with CWE-401, which describes missing release of memory after effective use, and CWE-789, concerning the general category of memory leaks in C and C++ applications. The attacker's role is limited to providing input data that forces the interpreter down the vulnerable code path. By constructing an MSL file containing a sequence of operations or specific nested structures that trigger repeated allocations without corresponding frees, an adversary can induce a steady increase in the process's working set size. This behavior does not require complex exploitation techniques beyond the ability to submit maliciously formatted input files for processing. The vulnerability is particularly insidious because it may manifest slowly over time if the affected ImageMagick instance operates as part of a long-running service, such as an image conversion API or a web application that processes user-uploaded images using MSL formats.
The operational impact of this memory leak is primarily centered on denial of service conditions. As the process continues to consume available system RAM without releasing it, the host machine's free memory pool diminishes rapidly. Once the physical memory and swap space are exhausted, the operating system’s out-of-memory killer may terminate the ImageMagick process abruptly, or in more severe scenarios involving shared hosting environments, other critical services running on the same server may be terminated due to resource starvation. This leads to service unavailability for legitimate users relying on image processing capabilities. In cloud-native deployments where auto-scaling policies are tied to memory usage metrics, this vulnerability could trigger unnecessary scaling events, leading to increased infrastructure costs and potential instability in microservice architectures that depend on consistent availability of the ImageMagick backend.
Mitigation strategies must focus on both immediate remediation and long-term architectural controls. The primary defense is upgrading to a patched version of ImageMagick where the memory management logic within the MSL decoder has been corrected to ensure all allocated resources are properly freed upon completion or error conditions. Organizations should also implement strict input validation policies, ensuring that only trusted sources can submit MSL files for processing and that file types are validated against expected schemas before parsing begins. Additionally, deploying resource limits such as cgroups in Linux environments or container memory constraints can contain the blast radius of any successful exploitation attempt by preventing a single process from consuming all available system resources. Monitoring tools should be configured to alert on abnormal spikes in memory consumption for services utilizing ImageMagick, allowing for rapid detection and response before total service failure occurs. This vulnerability is categorized under ATT&CK technique T1496, Resource Hijacking, specifically as part of the broader category of Denial of Service via resource exhaustion, highlighting its potential to disrupt operational continuity through systematic depletion of computational resources.