CVE-2026-84851 in Ion-C
Summary
by MITRE • 09/02/2026
An uncontrolled recursion issue exists in Amazon Ion-C versions before 1.1.6 that might allow a remote unauthenticated actor to craft Ion data that exhausts the native call stack and crashes the application using the library, resulting in a denial of service.
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Analysis
by VulDB Data Team • 09/03/2026
The vulnerability identified as an uncontrolled recursion issue within Amazon Ion-C prior to version 1.1.6 represents a critical flaw in how the parser handles nested or deeply structured data inputs. The Ion format is designed for efficient serialization and deserialization, but its flexibility allows for complex nesting of values such as lists, structs, and annotations. When an attacker crafts malicious Ion data containing excessively deep recursion levels, the library's parsing logic fails to enforce adequate depth limits on recursive function calls during the decoding process. This lack of boundary checking causes the application consuming the library to consume stack memory at a rapid rate until the native call stack is exhausted.
From a technical perspective, this flaw aligns with CWE-675, which describes operations with duplicate inputs that lead to unintended recursion or resource exhaustion. The root cause lies in the absence of robust input validation mechanisms specifically targeting recursive depth during the parsing phase. Unlike some parsers that maintain explicit counters for nesting levels and throw exceptions when a threshold is exceeded, this version of Ion-C relies on implicit stack growth without sufficient safeguards. Consequently, any remote unauthenticated actor can exploit this behavior by sending specially crafted payloads over network interfaces where the library is exposed, such as through an API endpoint or message queue consumer that processes incoming Ion data streams.
The operational impact of this vulnerability is primarily a denial of service condition for applications relying on Amazon Ion-C. When the native call stack is exhausted, the application typically crashes with a segmentation fault or similar fatal error, leading to immediate downtime and potential loss of availability for dependent services. In cloud-native environments where auto-scaling groups might attempt to restart crashed instances repeatedly due to persistent attack traffic, this can lead to significant resource waste and increased operational costs. Furthermore, if the crash occurs during critical transaction processing, it may result in data inconsistency or incomplete state transitions within the application logic.
This vulnerability is categorized under MITRE ATT&CK technique T1499, Endpoint Denial of Service, specifically reflecting methods that exploit software vulnerabilities to disrupt service availability rather than compromising confidentiality or integrity. The attack vector is remote and unauthenticated, which significantly increases its severity as it requires no prior access credentials. Defense in depth strategies should be employed to mitigate this risk. Immediate remediation involves upgrading Amazon Ion-C to version 1.1.6 or later where the recursion limits have been properly implemented. Additionally, organizations should implement input validation layers at network boundaries using web application firewalls that can detect and block excessively deep nesting patterns before they reach the vulnerable library. Monitoring for abnormal memory usage spikes in processes utilizing this library can also serve as an early detection mechanism for ongoing exploitation attempts.