CVE-2026-104020 in ion-python
Summary
by MITRE • 10/01/2026
Uncontrolled recursion in the Ion reader in Amazon Ion Python before 0.15.0 might allow a remote unauthenticated actor to crash the application using the library, resulting in a denial of service, via a crafted, deeply nested Ion value.
To remediate this issue, users should upgrade to version 0.15.0 or later.
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Analysis
by VulDB Data Team • 10/01/2026
The vulnerability identified as Uncontrolled Recursion within the Amazon Ion Python reader prior to version 0.15.0 represents a critical resource exhaustion flaw that can be exploited by remote unauthenticated actors to cause a denial of service against applications utilizing this library. The core technical issue stems from how the parser handles deeply nested data structures inherent in the Amazon Ion format, which supports complex hierarchical representations similar to JSON but with additional type annotations and binary formats. When the reader encounters an excessively deep nesting level within a crafted Ion value, it triggers recursive function calls without adequate safeguards or depth limits. This uncontrolled recursion leads to rapid consumption of system stack space, ultimately resulting in a stack overflow condition that crashes the application process.
From a technical perspective, this flaw is classified under CWE-675, which denotes operations with duplicate resources, specifically where an operation uses multiple resources for the same task without limiting their use, leading to resource exhaustion. In the context of parsing libraries, unbounded recursion is a common attack vector because parsers often rely on recursive descent algorithms to navigate nested structures like lists and structs in Ion data. Without explicit depth tracking or iterative alternatives, maliciously crafted inputs can force the interpreter into an infinite loop of function calls until the operating system terminates the process due to stack overflow limits being exceeded. This behavior aligns with ATT&CK technique T1499, Endpoint Denial of Service, where attackers leverage software vulnerabilities to disrupt availability rather than compromising confidentiality or integrity.
The operational impact of this vulnerability is significant for any service that processes untrusted Ion data streams. Since the attack requires no authentication and can be triggered remotely via network requests containing malformed payloads, it poses a severe risk to web services, API gateways, or message queue consumers that ingest Ion-formatted messages. A successful exploitation results in immediate application termination, leading to downtime for dependent systems and potential loss of service availability. In high-throughput environments, an attacker could sustain this denial-of-service condition by sending multiple crafted requests, effectively rendering the service unusable until manual intervention is performed to restart the affected processes.
To mitigate this risk, organizations must upgrade the Amazon Ion Python library to version 0.15.0 or later, where developers have implemented safeguards such as maximum recursion depth limits or iterative parsing mechanisms that prevent stack overflow scenarios. Additionally, defensive coding practices should be adopted by implementing input validation layers at the network perimeter or application entry points to reject payloads with excessive nesting levels before they reach the parser. Monitoring for abnormal memory usage patterns associated with recursive operations can also aid in early detection of such attacks, ensuring rapid response capabilities are in place alongside timely software updates.