CVE-2024-30251 is a vulnerability classified under CWE-835 (Loop with Unreachable Exit Condition) found in aiohttp, an asynchronous HTTP client/server framework widely used in Python applications for handling HTTP requests asynchronously. The flaw exists in versions prior to 3.9.4, where processing a specially crafted multipart/form-data POST request causes the aiohttp server to enter an infinite loop. This infinite loop prevents the server from processing any further requests, effectively causing a denial-of-service (DoS) condition. The vulnerability requires no privileges or user interaction, making it remotely exploitable over the network by any unauthenticated attacker. The root cause is a logic error in the request parsing code that fails to reach an exit condition under certain malformed input scenarios. The vulnerability was publicly disclosed on May 2, 2024, with a CVSS v3.1 base score of 7.5 (high severity), reflecting its network attack vector, low complexity, no privileges required, and high impact on availability. No known exploits are currently reported in the wild, but the ease of exploitation and impact on availability make it a significant threat. The issue has been addressed in aiohttp version 3.9.4, with users recommended to upgrade or apply manual patches if upgrading is not feasible.

For European organizations, this vulnerability poses a significant risk of denial-of-service attacks against web applications and APIs built using vulnerable aiohttp versions. Organizations relying on asynchronous Python frameworks for critical services—such as financial institutions, healthcare providers, government portals, and cloud service providers—may experience service outages or degraded performance if targeted. The attack requires only a single crafted HTTP request, enabling attackers to disrupt services with minimal effort and no authentication. This can lead to operational downtime, loss of customer trust, and potential regulatory repercussions under GDPR if service availability impacts data processing obligations. Additionally, organizations using aiohttp in microservices architectures or as part of larger distributed systems may face cascading failures due to blocked request handling. The lack of known exploits in the wild suggests a window of opportunity for proactive mitigation before widespread exploitation occurs.

The primary mitigation is to upgrade all aiohttp deployments to version 3.9.4 or later, where the infinite loop vulnerability has been fixed. For organizations unable to upgrade immediately, applying the official patch or backporting the fix to their current version is critical. Network-level protections such as Web Application Firewalls (WAFs) should be configured to detect and block suspicious multipart/form-data POST requests that could trigger the vulnerability, although crafting precise signatures may be challenging. Rate limiting and anomaly detection on HTTP POST requests can help reduce the risk of exploitation. Monitoring aiohttp server logs for unusual request patterns or repeated multipart/form-data POST requests can provide early warning signs. Additionally, isolating aiohttp services behind reverse proxies or API gateways can add an extra layer of filtering and resilience. Regular security assessments and penetration testing should include attempts to exploit this vulnerability to verify mitigation effectiveness.