CVE-2025-3857: Amazon.IonDotnet DOS Vulnerability

CVE-2025-3857 Overview

CVE-2025-3857 is a denial of service vulnerability affecting the Amazon.IonDotnet library, specifically within the RawBinaryReader class used for parsing binary Ion data. When reading binary Ion data through this class, the library fails to properly check the number of bytes read from the underlying stream during deserialization. If malformed or truncated Ion data is processed, this oversight triggers an infinite loop condition that could result in a denial of service attack against applications using the vulnerable library.

Critical Impact

This vulnerability allows remote attackers to cause denial of service through malformed binary Ion data, potentially rendering applications and services unavailable without requiring authentication.

Affected Products

• Amazon.IonDotnet versions prior to 1.3.1
• Applications using RawBinaryReader class for binary Ion parsing
• Any forked or derivative code based on vulnerable Amazon.IonDotnet versions

Discovery Timeline

• 2025-04-21 - CVE CVE-2025-3857 published to NVD
• 2025-10-14 - Last updated in NVD database

Technical Details for CVE-2025-3857

Vulnerability Analysis

This vulnerability is classified under CWE-502 (Deserialization of Untrusted Data). The core issue lies in the RawBinaryReader class's handling of binary Ion format deserialization. During the parsing process, the reader does not validate the number of bytes consumed from the input stream against expected values. This lack of validation becomes problematic when processing malformed or intentionally truncated Ion binary data.

When an attacker supplies crafted Ion data that indicates a certain data length but provides fewer bytes than specified, the reader enters a state where it continuously attempts to read data that doesn't exist, creating an infinite loop. This condition persists indefinitely, consuming CPU resources and preventing the application from processing other requests.

The vulnerability can be exploited remotely over a network connection by any attacker who can supply Ion data to an affected application. No authentication or user interaction is required to trigger the condition, making it particularly dangerous for public-facing services that parse user-supplied Ion data.

Root Cause

The root cause is insufficient input validation in the RawBinaryReader class during binary Ion format deserialization. The reader trusts length fields within the Ion binary format without verifying that the specified number of bytes are actually available in the input stream. When the actual data is shorter than indicated by these length fields, the reader fails to detect the end-of-stream condition and continues attempting to read indefinitely.

Attack Vector

The attack vector is network-based, requiring an attacker to supply maliciously crafted binary Ion data to an application using Amazon.IonDotnet. The attack does not require any privileges or user interaction. An attacker can construct truncated or malformed Ion binary data where the header indicates a specific payload size, but the actual data is shorter than specified. When this data is processed by the RawBinaryReader, the infinite loop is triggered.

Attack scenarios include:

• Submitting malformed Ion data through API endpoints that accept Ion-formatted payloads
• Sending crafted messages to services using Ion for data serialization
• Uploading malicious Ion files to applications that process user-supplied binary data

Detection Methods for CVE-2025-3857

Indicators of Compromise

• Abnormally high CPU utilization on services processing Ion data
• Application threads stuck in parsing operations without completion
• Timeouts and unresponsive behavior in services that accept Ion input
• Memory consumption patterns indicating stuck reader operations

Detection Strategies

• Monitor for processes or threads with sustained 100% CPU usage during Ion parsing operations
• Implement application-level timeouts for deserialization operations
• Use dependency scanning tools to identify Amazon.IonDotnet versions prior to 1.3.1
• Deploy network monitoring to detect unusual patterns in Ion data submissions

Monitoring Recommendations

• Configure alerting for CPU spikes correlated with Ion data processing endpoints
• Implement health checks that verify parsing operations complete within expected timeframes
• Enable detailed logging for deserialization operations to identify stuck parsers
• Monitor application thread pools for threads blocked in RawBinaryReader operations

How to Mitigate CVE-2025-3857

Immediate Actions Required

• Upgrade Amazon.IonDotnet to version 1.3.1 or later immediately
• Review and patch any forked or derivative code incorporating the vulnerable library
• Implement input validation and size limits on Ion data before processing
• Add timeout mechanisms around Ion deserialization operations as a defensive measure

Patch Information

Amazon has released version 1.3.1 of Amazon.IonDotnet which addresses this vulnerability. The fix ensures proper validation of bytes read from the underlying stream during binary Ion deserialization, preventing the infinite loop condition. Users should upgrade by updating their NuGet package reference to Amazon.IonDotnet version 1.3.1 or later.

For complete details, refer to the AWS Security Bulletin AWS-2025-009 and the GitHub Security Advisory GHSA-gm2p-wf5c-w3pj. The patched release is available at the GitHub Release v1.3.1.

Workarounds

• Implement strict timeout limits on all Ion deserialization operations to prevent indefinite hangs
• Validate Ion data size and structure before passing to RawBinaryReader
• Consider using alternative parsing approaches with stream size validation until patching is complete
• Isolate Ion parsing operations in separate processes or containers to limit impact of resource exhaustion

# Update Amazon.IonDotnet via .NET CLI
dotnet add package Amazon.IonDotnet --version 1.3.1

# Verify installed version
dotnet list package | grep Amazon.IonDotnet