CVE-2026-85786 in ion-java
Summary
by MITRE • 09/04/2026
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.
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Analysis
by VulDB Data Team • 09/04/2026
The vulnerability identified in Amazon ion-java prior to version 1.12.1 stems from an improper handling of highly compressed data during the parsing and decompression processes. Specifically, while a previous remediation for CVE-2026-75936 introduced mechanisms to opt out of automatic GZIP auto-decompression, this fix was incomplete in its coverage. The library failed to adequately restrict or validate the expansion ratio of compressed Ion documents that are processed through remaining decompression pathways. This oversight allows an attacker to craft a maliciously small but highly optimized compressed Ion document designed to expand into an arbitrarily large size when decompressed by the application logic.
From a technical perspective, this flaw represents a classic resource exhaustion scenario often categorized under CWE-400: Uncontrolled Resource Consumption. The core issue lies in the lack of strict limits on the output buffer size or memory allocation during the inflation process. When the ion-java library encounters such a crafted payload, it attempts to allocate sufficient heap space to hold the expanded data structure without verifying whether the expansion factor exceeds safe thresholds. This behavior bypasses existing safeguards intended to prevent zip-slip and decompression bomb attacks, leaving the application vulnerable to rapid memory depletion.
The operational impact of this vulnerability is primarily focused on denial of service conditions for applications relying on ion-java for parsing Amazon Ion format data. By submitting a specially crafted compressed document, remote attackers can trigger excessive memory allocation within the Java Virtual Machine heap. This leads to OutOfMemoryError exceptions, application crashes, or significant performance degradation as the system struggles to manage the inflated data structures. In cloud-native environments where resources are dynamically allocated and monitored, such an event could cause cascading failures across dependent services that rely on stable availability of the ion-java processing component.
This vulnerability aligns with MITRE ATT&CK technique T1496: Resource Hijacking, specifically under sub-techniques related to computational cycle or bandwidth consumption through resource exhaustion. Attackers leverage this flaw not necessarily for data exfiltration but to disrupt service continuity and availability, which is a critical component of the CIA triad in security frameworks. The incomplete fix from the previous CVE highlights the importance of comprehensive regression testing when addressing decompression-related vulnerabilities, as partial mitigations may leave alternative attack vectors open.
To remediate this issue effectively, users must upgrade their ion-java dependency to version 1.12.1 or later. This release addresses the gaps in the GZIP auto-decompression opt-out mechanism by implementing stricter validation of expansion ratios and enforcing limits on decompressed data sizes. Organizations should also audit their usage of ion-java for any custom configurations that might bypass default safety checks. Additionally, deploying runtime application self-protection tools or web application firewalls with deep packet inspection capabilities can provide an additional layer of defense against malformed Ion payloads before they reach the vulnerable library code. Regular dependency updates and adherence to secure coding practices regarding input validation are essential strategies to mitigate such resource exhaustion risks in production environments.