CVE-2022-31019 is a medium-severity vulnerability affecting the Vapor web framework, a server-side Swift HTTP framework widely used for building web applications and APIs. The vulnerability arises from improper handling of automatic content decoding, specifically related to recursive array parsing in HTTP request bodies. An attacker can craft a specially designed HTTP POST request with deeply nested array parameters that cause unbounded, attacker-controlled stack growth. This recursive parsing leads to a classic buffer overflow condition (CWE-120), resulting in a stack overflow and ultimately causing the Vapor server process to crash. The vulnerability affects all Vapor versions prior to 4.61.1, where the issue has been fixed. Exploitation does not require authentication but does require the attacker to send a crafted HTTP request to the vulnerable server. The exploit vector is straightforward, involving a single HTTP request with a carefully constructed payload that triggers the recursive parsing flaw. While no known exploits have been observed in the wild, the vulnerability can cause denial of service (DoS) by crashing the server, impacting availability. No direct code execution or privilege escalation has been reported. The root cause is a failure to properly check input sizes during buffer copying in the recursive decoding logic, leading to stack exhaustion. This vulnerability highlights the risks of unbounded recursive data structures in web request parsing and the importance of input validation and bounds checking in server frameworks.

For European organizations using the Vapor framework in production environments, this vulnerability poses a risk primarily to service availability. An attacker can remotely trigger a denial of service by crashing the web server, potentially disrupting business-critical web applications or APIs. This can lead to downtime, loss of customer trust, and operational disruptions. Organizations in sectors with high reliance on web services, such as finance, e-commerce, healthcare, and public services, may experience significant impact if their Vapor-based services are targeted. Although the vulnerability does not appear to allow remote code execution or data breaches, repeated or targeted DoS attacks could be used as part of larger attack campaigns or to distract from other malicious activities. The lack of authentication requirement increases the attack surface, allowing any external attacker to exploit the flaw if the server is exposed to the internet. Additionally, organizations with automated monitoring and incident response may face increased alert volumes and resource consumption due to repeated exploit attempts. The impact is mitigated if Vapor is deployed behind web application firewalls or reverse proxies that can detect and block malformed requests. However, direct exposure of vulnerable Vapor servers without such protections increases risk.

1. Upgrade all Vapor framework instances to version 4.61.1 or later, where the vulnerability has been patched. This is the most effective and recommended mitigation. 2. Implement strict input validation and request size limits at the web server or reverse proxy level to prevent excessively nested or large payloads from reaching the Vapor application. 3. Deploy web application firewalls (WAFs) with custom rules to detect and block recursive or suspiciously nested array parameters in HTTP requests. 4. Monitor server logs for unusual request patterns that match the exploit signature, such as deeply nested array parameters or repeated recursive keys. 5. Use rate limiting to reduce the impact of automated exploit attempts aiming to cause DoS. 6. Isolate Vapor applications in containerized or sandboxed environments to limit the blast radius of crashes. 7. Regularly audit and update dependencies and frameworks to ensure timely application of security patches. 8. Conduct security testing and fuzzing of input parsing components to identify similar recursive or buffer overflow issues proactively.