CVE-2025-49763 is a vulnerability classified under CWE-400 (Uncontrolled Resource Consumption) affecting the Apache Traffic Server, an open-source HTTP/1.1 and HTTP/2.0 compliant caching proxy server widely used for improving web performance and scalability. The vulnerability specifically resides in the Edge Side Includes (ESI) plugin, which is designed to assemble web pages from fragments. The issue arises because the ESI plugin lacks a limit on the maximum inclusion depth, meaning that a malicious actor can craft ESI instructions that recursively include content to an excessive depth. This uncontrolled recursion leads to excessive memory consumption, potentially exhausting system resources and causing denial of service (DoS) conditions. The affected versions include Apache Traffic Server releases from 9.0.0 through 9.2.10 and 10.0.0 through 10.0.5. The vendor has addressed this vulnerability by introducing a new configuration setting, --max-inclusion-depth, which allows administrators to limit the maximum depth of ESI inclusions, thereby preventing resource exhaustion. Users are strongly recommended to upgrade to versions 9.2.11 or 10.0.6 or later, where this fix is implemented. As of the publication date, there are no known exploits in the wild, but the potential for abuse exists given the nature of the vulnerability and the widespread use of Apache Traffic Server in caching and proxy roles within enterprise and service provider environments.

For European organizations, the impact of this vulnerability can be significant, particularly for those relying on Apache Traffic Server for web acceleration, caching, and proxy services. Exploitation could lead to denial of service by exhausting memory resources, resulting in service outages or degraded performance. This can affect critical web infrastructure, including content delivery networks (CDNs), e-commerce platforms, and public-facing government or financial services portals. The disruption could lead to loss of availability, impacting business continuity and customer trust. Additionally, resource exhaustion attacks may serve as a smokescreen for other malicious activities or be leveraged in multi-vector attacks. Given the role of Apache Traffic Server in handling large volumes of web traffic, the scope of impact can be broad, affecting multiple services and users simultaneously. The absence of authentication requirements or user interaction for triggering the vulnerability increases the risk, as attackers can exploit it remotely by sending crafted ESI instructions to vulnerable servers.

Beyond upgrading to Apache Traffic Server versions 9.2.11 or 10.0.6 or later, European organizations should implement the following specific mitigations: 1) Immediately configure the --max-inclusion-depth setting to a conservative value appropriate to the organization's typical ESI usage patterns to limit recursion depth and prevent resource exhaustion. 2) Employ network-level protections such as Web Application Firewalls (WAFs) or Intrusion Prevention Systems (IPS) to detect and block anomalous or excessively nested ESI requests. 3) Monitor server resource utilization closely, setting alerts for unusual memory consumption spikes that could indicate attempted exploitation. 4) Conduct regular audits of ESI usage and plugin configurations to ensure no unauthorized or unexpected changes have been made. 5) Isolate Apache Traffic Server instances handling untrusted or external traffic from critical internal networks to contain potential impact. 6) Implement rate limiting on incoming requests to reduce the risk of automated exploitation attempts. 7) Maintain an incident response plan that includes procedures for mitigating resource exhaustion attacks to minimize downtime.