CVE-2025-53628 is a medium severity vulnerability identified in the yhirose cpp-httplib, a widely used C++11 single-file header-only cross-platform HTTP/HTTPS library. Versions prior to 0.20.1 of cpp-httplib contain a flaw related to the handling of unique lines in HTTP requests, where there is no enforced limit on the length or number of unique lines processed. This absence of limits can be exploited by an attacker to trigger an infinite loop due to an unreachable exit condition (CWE-835) within the library's code. The infinite loop can lead to arbitrary memory allocation (CWE-770), potentially exhausting system resources and causing denial of service (DoS). The vulnerability does not require authentication or user interaction and can be triggered remotely over the network (AV:N, PR:N, UI:N). The CVSS 4.0 base score is 6.3, reflecting a medium severity level, with partial impacts on confidentiality, integrity, and availability. The vulnerability was fixed in version 0.20.1 of cpp-httplib. No known exploits are currently reported in the wild. This vulnerability is related to CVE-2025-53629, suggesting a cluster of issues in the same library version range. The infinite loop arises from a logic flaw where the exit condition for a processing loop is never met, allowing an attacker to craft malicious HTTP requests that cause the server or application using cpp-httplib to hang or consume excessive memory, leading to service disruption or potential crash.

For European organizations, the impact of CVE-2025-53628 primarily involves service availability and resource exhaustion risks. Organizations using cpp-httplib in their web services, APIs, or embedded HTTP/HTTPS clients may experience denial of service conditions if targeted by attackers sending specially crafted requests that exploit the infinite loop vulnerability. This can disrupt business-critical applications, degrade user experience, and potentially cause cascading failures in dependent systems. Although the vulnerability has limited direct impact on confidentiality or data integrity, the resulting downtime or degraded service availability can have significant operational and reputational consequences. Industries with high reliance on real-time or continuous web services, such as financial services, telecommunications, healthcare, and critical infrastructure sectors, are particularly at risk. Additionally, the lack of authentication or user interaction requirements means attackers can exploit this remotely and anonymously, increasing the threat surface. European organizations that develop or maintain software incorporating cpp-httplib, including IoT device manufacturers and embedded system developers, must also consider the risk of this vulnerability being exploited in supply chain attacks or embedded devices deployed in the field.

To mitigate CVE-2025-53628, European organizations should take the following specific actions: 1) Immediately identify all internal and third-party software components that use cpp-httplib versions earlier than 0.20.1. 2) Upgrade all affected instances of cpp-httplib to version 0.20.1 or later, where the vulnerability is patched. 3) If immediate upgrading is not feasible, implement network-level protections such as rate limiting, input validation, and anomaly detection to block or throttle suspicious HTTP requests with abnormally long or numerous unique lines. 4) Conduct thorough code reviews and static analysis on custom integrations of cpp-httplib to ensure no similar infinite loop conditions exist. 5) Monitor application logs and network traffic for signs of exploitation attempts, such as repeated requests causing high CPU or memory usage. 6) Engage with software vendors and supply chain partners to confirm they have addressed this vulnerability in their products. 7) Incorporate fuzz testing and boundary condition testing in development pipelines to detect similar logic flaws proactively. 8) For embedded or IoT devices using cpp-httplib, plan firmware updates or patches to remediate the vulnerability and consider network segmentation to limit exposure.