CVE-2025-55181 is a vulnerability classified under CWE-834 (Excessive Iteration) found in Facebook's proxygen HTTP library, version v2025.08.25.00. The flaw exists in the HTTPQuicCoroSession component, which handles HTTP/QUIC sessions asynchronously using coroutines. When an HTTP request or response body exceeding 2^31 bytes is received, the component enters an infinite loop. This loop blocks the backing event loop, preventing other operations from proceeding. During each iteration, data is unconditionally appended to a std::vector, causing unbounded memory growth. This behavior eventually leads to the process exhausting system memory, resulting in a denial of service (DoS) condition. The vulnerability can be triggered remotely without authentication or user interaction, making it accessible to unauthenticated attackers over the network. Although the CVSS score is 5.3 (medium severity), the impact is limited to availability, with no direct confidentiality or integrity compromise. No patches or fixes have been published at the time of disclosure, and no known exploits are reported in the wild. The vulnerability highlights a failure to properly validate or limit the size of HTTP message bodies, leading to resource exhaustion and service disruption.

For European organizations, the primary impact of CVE-2025-55181 is a denial of service condition affecting services relying on Facebook's proxygen library for HTTP/QUIC communication. This can disrupt web services, APIs, or internal communications that use proxygen, potentially causing downtime or degraded performance. Organizations handling large volumes of HTTP traffic or those exposed to untrusted networks are at higher risk. The unbounded memory consumption can lead to server crashes or require costly restarts, impacting business continuity and user experience. While confidentiality and integrity are not directly compromised, availability issues can indirectly affect compliance with service-level agreements (SLAs) and regulatory requirements such as GDPR, especially if critical services become unavailable. Additionally, the vulnerability could be leveraged as part of a broader attack strategy to exhaust resources and distract security teams.

To mitigate CVE-2025-55181, European organizations should implement strict limits on HTTP request and response body sizes at the network perimeter or within proxygen configurations if possible. Deploying web application firewalls (WAFs) or reverse proxies that enforce maximum payload sizes can prevent excessively large requests from reaching vulnerable components. Monitoring and alerting on abnormal HTTP payload sizes and unusual memory consumption patterns in proxygen processes can provide early detection of exploitation attempts. Isolating proxygen instances in containerized or sandboxed environments limits the blast radius of potential crashes. Organizations should also track updates from Facebook/Meta for patches addressing this vulnerability and plan prompt deployment once available. Reviewing and hardening QUIC and HTTP/2 traffic handling configurations can reduce exposure. Finally, conducting regular stress testing and resilience assessments helps ensure systems can handle edge cases without failure.