CVE-2025-27598: Sixlabors ImageSharp DoS Vulnerability

CVE-2025-27598 Overview

CVE-2025-27598 is an Out-of-bounds Write vulnerability discovered in the ImageSharp GIF decoder component. ImageSharp is a popular 2D graphics API used extensively in .NET applications for image processing and manipulation. This vulnerability allows attackers to craft malicious GIF files that, when processed by vulnerable versions of ImageSharp, can cause the application to crash due to improper memory handling during GIF decoding operations.

Critical Impact

Attackers can exploit this vulnerability to cause denial of service conditions in applications that process user-supplied GIF images using ImageSharp, potentially disrupting critical services that rely on image processing functionality.

Affected Products

• SixLabors ImageSharp versions prior to v3.1.7
• SixLabors ImageSharp versions prior to v2.1.10
• Applications using vulnerable ImageSharp library for GIF image processing

Discovery Timeline

• 2025-03-06 - CVE-2025-27598 published to NVD
• 2025-03-24 - Last updated in NVD database

Technical Details for CVE-2025-27598

Vulnerability Analysis

This vulnerability is classified as CWE-787 (Out-of-bounds Write), a memory corruption issue that occurs when the GIF decoder writes data beyond the boundaries of allocated memory buffers. The vulnerability exists within ImageSharp's GIF decoding logic, which fails to properly validate frame dimensions or buffer sizes when processing specially crafted GIF images. When an attacker supplies a malicious GIF with manipulated frame data or dimensions, the decoder attempts to write pixel data outside the intended memory region, resulting in memory corruption and application termination.

The network-accessible nature of this vulnerability is particularly concerning for web applications and services that accept user-uploaded images. Since GIF processing typically occurs server-side without user interaction, attackers can remotely trigger the vulnerability by simply uploading a malicious file through any image upload endpoint that uses ImageSharp.

Root Cause

The root cause lies in insufficient bounds checking within the GIF decoder implementation. When processing GIF frames, the decoder does not adequately verify that the frame dimensions and write operations stay within the allocated buffer boundaries. This allows specially constructed GIF files to trigger write operations that exceed the designated memory space, corrupting adjacent memory regions and causing the application to crash.

Attack Vector

The attack can be executed remotely over the network without requiring authentication or user interaction. An attacker crafts a malicious GIF file with manipulated header information or frame data designed to trigger the out-of-bounds write condition. When a vulnerable application attempts to decode this GIF file—whether through file upload, URL fetching, or any other image processing pipeline—the corrupted data causes the decoder to write beyond buffer boundaries, resulting in a crash.

Attack scenarios include:

• Uploading malicious GIF files to web applications that process images
• Sending crafted GIF files via APIs that accept image input
• Including malicious GIFs in content that will be processed by backend services
• Embedding malicious GIFs in documents or emails processed by ImageSharp-based tools

Detection Methods for CVE-2025-27598

Indicators of Compromise

• Unexpected application crashes during GIF image processing operations
• Core dumps or crash logs indicating memory access violations in ImageSharp assemblies
• Repeated crash events correlated with specific image upload or processing activities
• Error logs showing AccessViolationException or similar memory-related exceptions during GIF decoding

Detection Strategies

• Monitor application logs for crashes related to ImageSharp image processing, particularly in GIF decoding modules
• Implement file integrity monitoring on uploaded images to detect anomalous GIF file structures
• Deploy application-level exception monitoring to capture and analyze crashes in image processing code paths
• Use dependency scanning tools to identify vulnerable ImageSharp versions in your software inventory

Monitoring Recommendations

• Configure alerting for repeated application crashes in services that handle image processing
• Implement anomaly detection on image upload endpoints to identify unusual patterns of GIF file submissions
• Monitor system resource utilization for signs of denial of service attempts targeting image processing
• Enable detailed logging for image processing operations to aid in incident investigation

How to Mitigate CVE-2025-27598

Immediate Actions Required

• Upgrade ImageSharp to version v3.1.7 or later for the 3.x branch, or v2.1.10 or later for the 2.x branch
• Conduct a software inventory to identify all applications using ImageSharp and prioritize patching
• Consider temporarily disabling GIF processing capabilities if immediate patching is not feasible
• Implement input validation to reject suspicious or malformed GIF files at upload boundaries

Patch Information

SixLabors has released security patches to address this vulnerability. Users on the 3.x branch should upgrade to version v3.1.7 or later, while users on the 2.x branch should upgrade to version v2.1.10 or later. The fix addresses the bounds checking issue in the GIF decoder to prevent out-of-bounds write operations. Technical details about the patch can be found in the GitHub Pull Request #2890 and the GitHub Security Advisory GHSA-2cmq-823j-5qj8.

Workarounds

• Implement file type validation to reject GIF files from untrusted sources until patching is complete
• Use a Web Application Firewall (WAF) to filter potentially malicious image uploads
• Isolate image processing services in sandboxed environments to limit the impact of crashes
• Consider using alternative image processing libraries for GIF handling as a temporary measure

# Update ImageSharp via NuGet Package Manager Console
# For 3.x branch:
Update-Package SixLabors.ImageSharp -Version 3.1.7

# For 2.x branch:
Update-Package SixLabors.ImageSharp -Version 2.1.10

# Or via .NET CLI:
dotnet add package SixLabors.ImageSharp --version 3.1.7