Uncontrolled memory allocation in the binary Ion stream cursor in Amazon ion-java before 1.12.0 might allow remote actors to cause a denial of service via a crafted Ion binary document containing a declared-length field that causes excessive heap preallocation.

To remediate this issue, users should upgrade to version 1.12.0.

Improper handling of highly compressed data in the GZIP auto-decompression handler in Amazon ion-java before 1.12.0 might allow remote actors to cause a denial of service via a crafted compressed Ion document that expands to an arbitrarily large size upon decompression.

To remediate this issue, users should upgrade to version 1.12.0 and configure withGzipDecompressionEnabled(false) and/or set an explicit withMaximumBufferSize() when parsing untrusted input.

Improper handling of highly compressed data in Amazon ion-java before 1.12.1 might allow remote attackers to cause a denial of service via a crafted compressed Ion document that expands to an arbitrarily large size upon decompression due to insufficient coverage of the GZIP auto-decompression opt-out introduced for CVE-2026-75936.

To remediate this issue, users should upgrade to version 1.12.1.

Amazon Ion is a Java implementation of the Ion data notation. Prior to version 1.10.5, a potential denial-of-service issue exists in ion-java for applications that use ion-java to deserialize Ion text encoded data, or deserialize Ion text or binary encoded data into the IonValue model and then invoke certain IonValue methods on that in-memory representation. An actor could craft Ion data that, when loaded by the affected application and/or processed using the IonValue model, results in a StackOverflowError originating from the ion-java library. The patch is included in ion-java 1.10.5. As a workaround, do not load data which originated from an untrusted source or that could have been tampered with.