CVE-2024-21634 is a vulnerability classified under CWE-770 (Allocation of Resources Without Limits or Throttling) affecting the amazon-ion Java library (ion-java) before version 1.10.5. Amazon Ion is a data serialization format and ion-java is its Java implementation used to deserialize Ion text or binary encoded data into an in-memory IonValue model. The vulnerability manifests when an attacker crafts malicious Ion data that, upon deserialization and subsequent method invocation on the IonValue object, triggers excessive recursive calls or unbounded resource consumption leading to a StackOverflowError. This error results in a denial-of-service (DoS) condition by crashing or destabilizing the affected application. The flaw does not require any privileges or user interaction and can be exploited remotely by supplying malicious Ion data to the vulnerable application. The CVSS v3.1 score is 7.5, reflecting high severity due to network attack vector, low attack complexity, no privileges required, no user interaction, and impact limited to availability. No known exploits have been reported in the wild yet. The vulnerability is patched in ion-java version 1.10.5, and the recommended mitigation is to upgrade to this or later versions. As a temporary workaround, applications should avoid loading Ion data from untrusted or potentially tampered sources to prevent exploitation.

For European organizations, the primary impact is denial of service affecting availability of applications that utilize ion-java for processing Ion data. This can disrupt business operations, especially in sectors relying on real-time data processing, cloud services, or microservices architectures that use Ion serialization. The vulnerability does not compromise confidentiality or integrity but can cause application crashes or service outages, potentially leading to financial losses, reputational damage, and regulatory scrutiny under laws like GDPR if service availability is critical. Organizations in finance, e-commerce, telecommunications, and cloud service providers in Europe are particularly at risk if they use affected versions of ion-java. The lack of authentication or user interaction requirements means attackers can exploit this remotely, increasing the threat surface. Although no active exploits are known, the high CVSS score and ease of exploitation warrant prompt remediation to avoid potential future attacks.

1. Upgrade all instances of ion-java to version 1.10.5 or later immediately to apply the official patch addressing this vulnerability. 2. Implement strict input validation and filtering to reject Ion data from untrusted or unauthenticated sources before deserialization. 3. Employ runtime application monitoring to detect abnormal resource consumption or crashes related to Ion data processing. 4. Use application-layer firewalls or API gateways to restrict or inspect incoming Ion data payloads, blocking suspicious or malformed inputs. 5. Conduct code audits and dependency scans to identify all usages of ion-java and ensure no legacy versions remain in production or development environments. 6. Develop incident response plans that include steps to isolate and recover from DoS conditions caused by this vulnerability. 7. Educate developers and security teams about safe deserialization practices and the risks of processing untrusted data formats like Ion. 8. Where possible, sandbox or isolate components handling Ion data to limit the impact of potential crashes.