CVE-2025-53633 is a high-severity vulnerability affecting the ctfer-io chall-manager platform, a system designed to start Challenges on Demand for players in a platform-agnostic manner. The vulnerability arises from improper handling of zip archive decompression during scenario decoding. Specifically, the system does not verify the size of the decompressed content, which allows an attacker to craft a malicious zip archive (commonly known as a zip bomb) that expands to consume excessive system resources. This leads to asymmetric resource consumption or amplification, potentially causing denial of service (DoS) conditions by exhausting CPU, memory, or disk space. Notably, exploitation requires no authentication or authorization, meaning any remote attacker can trigger this vulnerability without user interaction or credentials. However, the vendor recommends deploying chall-manager deep within protected infrastructure layers to reduce exposure. The vulnerability affects all versions prior to 0.1.4, with a patch released in version 0.1.4 that mitigates the issue by implementing size checks on decompressed content. The CVSS 4.0 score is 8.7 (high), reflecting the network attack vector, no required privileges or user interaction, and a high impact on availability. There are no known exploits in the wild as of the publication date, but the ease of exploitation and potential impact make it a critical concern for organizations using this product.

For European organizations using ctfer-io chall-manager, this vulnerability poses a significant risk to system availability and operational continuity. An attacker could remotely deploy a zip bomb to exhaust server resources, leading to service outages or degraded performance. This is particularly critical in environments where chall-manager is integrated into competitive or training platforms, such as cybersecurity competitions, educational institutions, or research labs. The lack of authentication requirements increases the attack surface, potentially allowing external threat actors to disrupt services without insider access. Additionally, if chall-manager is part of a larger infrastructure handling sensitive or time-critical challenges, the DoS could cascade, affecting dependent systems and users. European organizations with strict uptime requirements or regulatory obligations around service availability (e.g., financial institutions, critical infrastructure operators) may face compliance risks or reputational damage if impacted. Although the vendor recommends isolating chall-manager within secure network segments, misconfigurations or exposure to public networks could increase exploitation likelihood.

1. Immediate upgrade to ctfer-io chall-manager version 0.1.4 or later, which includes the patch to validate decompressed content size and prevent zip bomb exploitation. 2. Network segmentation: Ensure chall-manager instances are deployed within isolated, internal network zones inaccessible from the public internet or untrusted networks. 3. Implement strict ingress filtering and firewall rules to restrict access to the chall-manager service only to trusted IP addresses or VPNs. 4. Monitor resource usage closely on servers running chall-manager for unusual spikes in CPU, memory, or disk utilization that may indicate exploitation attempts. 5. Employ application-layer controls such as file upload size limits and scanning of uploaded archives for malicious content before processing. 6. Conduct regular security audits and penetration tests focusing on chall-manager deployment to verify proper isolation and patch status. 7. Maintain up-to-date incident response plans to quickly identify and mitigate DoS attacks stemming from this vulnerability.