CVE-2025-11573: Amazon.IonDotnet DoS Vulnerability

CVE-2025-11573 Overview

An infinite loop vulnerability exists in the Amazon.IonDotnet library versions prior to v1.3.2. This denial of service vulnerability allows threat actors to exploit improper input validation through specially crafted text input, causing the library to enter an infinite loop and consume excessive CPU resources. The vulnerability is particularly concerning as the library has been deprecated as of August 20, 2025, meaning no further security updates will be released beyond the final patch.

Critical Impact

Applications using Amazon.IonDotnet prior to v1.3.2 are vulnerable to denial of service attacks via specially crafted text input that triggers an infinite loop, potentially rendering services unresponsive.

Affected Products

• Amazon.IonDotnet versions prior to v1.3.2
• Applications and services utilizing the Amazon Ion data serialization format via the .NET library
• AWS services or custom applications dependent on ion-dotnet for data parsing

Discovery Timeline

• October 9, 2025 - CVE-2025-11573 published to NVD
• October 14, 2025 - Last updated in NVD database

Technical Details for CVE-2025-11573

Vulnerability Analysis

This vulnerability is classified under CWE-1286 (Improper Validation of Syntactically Incorrect Input). The Amazon.IonDotnet library, which provides .NET support for the Amazon Ion data serialization format, fails to properly validate certain text inputs during parsing operations. When malformed or specially crafted text data is supplied to the library, the parsing logic enters an infinite loop rather than gracefully handling the invalid input or terminating with an appropriate error.

The network-accessible nature of this vulnerability means that any service accepting Ion-formatted data from untrusted sources could be exploited remotely without requiring authentication. An attacker only needs to send a single malicious request containing the crafted payload to trigger the denial of service condition.

Root Cause

The root cause of this vulnerability lies in improper validation of syntactically incorrect input within the text parsing routines of the Amazon.IonDotnet library. The parser contains a code path that fails to recognize certain malformed input patterns as invalid, causing the parsing state machine to loop indefinitely without advancing through the input or reaching a termination condition. This represents a failure in boundary condition handling where edge cases in the input grammar are not properly accounted for.

Attack Vector

The attack vector is network-based, requiring no authentication or user interaction. An attacker can exploit this vulnerability by:

1. Identifying an application endpoint that accepts Amazon Ion text format data
2. Crafting a specially malformed text payload designed to trigger the infinite loop condition
3. Sending the malicious payload to the target application
4. The vulnerable parsing code enters an infinite loop, consuming CPU resources and potentially blocking the processing thread

The vulnerability mechanism involves the parser failing to properly handle syntactically incorrect input, leading to an algorithmic complexity attack scenario. For detailed technical information, refer to the GitHub Security Advisory GHSA-q5r6-9qwq-g2wj.

Detection Methods for CVE-2025-11573

Indicators of Compromise

• Abnormally high CPU utilization on services processing Ion-formatted data
• Thread pool exhaustion or application hangs during Ion text parsing operations
• Increased response times or timeouts from services accepting Ion input
• Log entries indicating parsing operations that never complete

Detection Strategies

• Monitor application dependencies for Amazon.IonDotnet versions prior to v1.3.2
• Implement CPU usage anomaly detection on services processing Ion data
• Deploy application-level timeout monitoring for Ion parsing operations
• Use SentinelOne Singularity to detect abnormal process behavior patterns indicative of denial of service conditions

Monitoring Recommendations

• Configure alerting thresholds for sustained high CPU usage on Ion-processing services
• Implement request timeout monitoring at the application layer
• Track thread utilization metrics to detect blocked or infinitely looping threads
• Enable detailed logging for Ion parsing operations to identify problematic inputs

How to Mitigate CVE-2025-11573

Immediate Actions Required

• Upgrade Amazon.IonDotnet to version v1.3.2 immediately
• Audit all applications and services for dependencies on vulnerable library versions
• Consider migrating away from Amazon.IonDotnet as the library is deprecated and will not receive future updates
• Implement input validation and request timeouts as defense-in-depth measures

Patch Information

Amazon has released version v1.3.2 of the IonDotnet library which addresses this vulnerability. The patch can be obtained from the GitHub Release v1.3.2. For additional details, refer to the AWS Security Bulletin AWS-2025-022.

Important: As of August 20, 2025, the Amazon.IonDotnet library has been deprecated and will not receive further updates. Organizations should plan migration to alternative solutions for long-term support.

Workarounds

• Implement request timeouts at the application layer to terminate long-running parsing operations
• Deploy input size limits to reduce the attack surface for crafted payloads
• Use network-level rate limiting to mitigate denial of service impact
• Consider isolating Ion parsing operations in separate processes with resource constraints

# Example: Upgrade Amazon.IonDotnet via NuGet
dotnet add package Amazon.IonDotnet --version 1.3.2

# Verify installed version
dotnet list package | grep IonDotnet