CVE-2025-3857

Amazon.IonDotnet (ion-dotnet) is a .NET library with an implementation of the Ion data serialization format.

An issue exists in Amazon.IonDotnet and the RawBinaryReader class where, under certain conditions, an actor could trigger an infinite loop condition.

Workarounds

There are no workarounds. Upgrade to version 1.3.1.

References

If you have any questions or comments about this advisory, contact AWS/Amazon Security via our vulnerability reporting page or directly via email to [email protected]. Please do not create a public GitHub issue.

Credit

We would like to thank Josh Coleman from Symbotic for collaborating on this issue through the coordinated vulnerability disclosure process.

When reading binary Ion data through Amazon.IonDotnet using the RawBinaryReader class, Amazon.IonDotnet does not check the number of bytes read from the underlying stream while deserializing the binary format. If the Ion data is malformed or truncated, this triggers an infinite loop condition that could potentially result in a denial of service.

Impacted versions: <=1.3.0

Untrusted serialized data is processed by a deserializer that can instantiate arbitrary objects or execute code as a side effect. Typical impact: arbitrary code execution or logic abuse.

CVE-2025-3857 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.3.1); upgrading removes the vulnerable code path.

Kodem intelligence

This issue has been addressed in Amazon.IonDotnet version 1.3.1. We recommend upgrading to the latest version and ensuring any forked or derivative code is patched to incorporate the new fixes.

1. What is CVE-2025-3857? CVE-2025-3857 is a high-severity insecure deserialization vulnerability in Amazon.IonDotnet (nuget), affecting versions < 1.3.1. It is fixed in 1.3.1. Untrusted serialized data is processed by a deserializer that can instantiate arbitrary objects or execute code as a side effect.
2. How severe is CVE-2025-3857? CVE-2025-3857 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of Amazon.IonDotnet are affected by CVE-2025-3857? Amazon.IonDotnet (nuget) versions < 1.3.1 is affected.
4. Is there a fix for CVE-2025-3857? Yes. CVE-2025-3857 is fixed in 1.3.1. Upgrade to this version or later.
5. Is CVE-2025-3857 exploitable, and should I be worried? Whether CVE-2025-3857 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2025-3857 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2025-3857? Upgrade Amazon.IonDotnet to 1.3.1 or later.