CVE-2025-3857 is a medium-severity vulnerability affecting the Amazon Ion Dotnet library, specifically the RawBinaryReader class used for deserializing binary Ion data. The vulnerability arises because the RawBinaryReader does not properly verify the number of bytes read from the underlying stream during deserialization. When processing malformed or truncated Ion binary data, this lack of validation can cause the deserialization process to enter an infinite loop, as the loop controlling the read operation has an unreachable exit condition. This infinite loop leads to a denial of service (DoS) condition by causing the consuming application to hang or consume excessive CPU resources, potentially degrading system availability. The vulnerability is categorized under CWE-835 (Loop with Unreachable Exit Condition) and CWE-502 (Deserialization of Untrusted Data), highlighting that the root cause is improper handling of untrusted input data during deserialization. The issue affects all versions prior to Amazon.IonDotnet 1.3.1, and users are advised to upgrade to version 1.3.1 or later. No known exploits have been reported in the wild as of the publication date, but the vulnerability poses a risk to any application or service that uses this library to process untrusted or external Ion binary data streams. The infinite loop can be triggered remotely if an attacker can supply crafted Ion data to the vulnerable system, making it a potential vector for denial of service attacks in distributed or cloud environments where Amazon Ion Dotnet is used.

For European organizations, the primary impact of this vulnerability is a denial of service condition that can disrupt business-critical applications relying on Amazon Ion Dotnet for data serialization and deserialization. This can affect cloud services, data processing pipelines, and microservices architectures that use Ion data formats, potentially leading to service outages or degraded performance. The infinite loop can cause resource exhaustion on affected servers, impacting availability and possibly cascading to other dependent systems. Confidentiality and integrity are less directly impacted since the vulnerability does not allow code execution or data manipulation, but availability degradation can still cause significant operational and reputational damage. Organizations in sectors such as finance, telecommunications, and cloud service providers—where Amazon Ion Dotnet might be integrated—could face service interruptions. Additionally, if the vulnerable component is part of a larger supply chain or third-party software stack, the impact could extend beyond the immediate application. Given the increasing adoption of Amazon Ion for efficient data interchange, especially in cloud-native environments, the risk of exploitation grows as more organizations process untrusted Ion data streams.

1. Immediate upgrade to Amazon.IonDotnet version 1.3.1 or later is essential to incorporate the fix that prevents the infinite loop condition. 2. Audit all internal and third-party applications and services that utilize Amazon Ion Dotnet to identify vulnerable versions and ensure timely patching. 3. Implement input validation and sanitization controls upstream to detect and reject malformed or truncated Ion data before it reaches the deserialization layer. 4. Employ runtime monitoring and resource usage alerts to detect anomalous CPU or memory consumption indicative of infinite loops or denial of service conditions. 5. Where feasible, isolate services handling untrusted Ion data in sandboxed or containerized environments to limit the impact of potential DoS attacks. 6. Review and update incident response plans to include scenarios involving deserialization vulnerabilities and denial of service conditions. 7. For organizations maintaining forks or derivative versions of Amazon Ion Dotnet, ensure patches from version 1.3.1 are backported and tested thoroughly. 8. Engage with vendors or cloud providers to confirm that underlying platforms have addressed this vulnerability if Amazon Ion Dotnet is used as part of managed services.