Amazon ion-java CVE-2026-75936

Exploitation requires three conditions: (1) the target application uses ion-java version 1.9.0 through 1.11.x; (2) the application has not explicitly disabled GZIP auto-decompression via withGzipDecompressionEnabled(false) - the vulnerable behavior is on by default; and (3) the application accepts Ion-format input from network-accessible, attacker-controlled sources without pre-validating or size-limiting compressed payloads before passing them to the parser. The CVSS 4.0 vector (AV:N/AC:L/PR:N/UI:N) confirms no authentication or user interaction is required once these conditions are met. Applications that parse Ion documents only from trusted internal producers, those that have already applied explicit buffer limits, and those that disable GZIP decompression are not exploitable through this vector.

The CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:N/UI:N/VA:H) accurately models the threat: any network-reachable service that ingests Ion documents from untrusted sources via the default ion-java configuration is exploitable without authentication or special attacker capabilities. The 8.7 score is credible and the primary real-world limiter is deployment context - applications that parse Ion data exclusively from internal trusted sources, or that pre-validate format before reaching ion-java, face significantly reduced exposure. No EPSS score was included in the source intelligence, and no CISA KEV listing exists, indicating no confirmed active exploitation at time of analysis. The DoS-only impact (VC:N/VI:N/VA:H, no confidentiality or integrity effect) may lower business priority relative to RCE vulnerabilities; however, uncontrolled heap exhaustion in a core parsing library can cascade into broader service outages in microservice architectures where the affected component is a critical path dependency. The fix is available and low-risk to apply, making remediation the clear priority.

An attacker sends a crafted GZIP-compressed binary Ion document - potentially only a few kilobytes in compressed form - to any network endpoint backed by ion-java in its default configuration. The library's auto-decompression handler expands the payload in-memory without limit, consuming gigabytes of JVM heap until an OutOfMemoryError is thrown or the OS terminates the process, denying service to all legitimate users. No public proof-of-concept code has been identified at time of analysis, but the decompression bomb technique (CWE-409) is well-documented and straightforward to implement using standard GZIP tooling.