CVE-2025-54581 is a high-severity vulnerability affecting versions 2.3.3 and below of vproxy, an HTTP/HTTPS/SOCKS5 proxy server developed by 0x676e67. The flaw arises from improper handling of the TTL (Time To Live) value parsed from the user-controlled HTTP Proxy-Authorization header. Specifically, the vulnerability is a divide-by-zero error (CWE-369) triggered when an attacker supplies a TTL value of zero, for example by crafting a username such as 'configuredUser-ttl-0'. This TTL value is passed into the function parse_ttl_extension, where a modulo operation 'timestamp % ttl' is performed. Since the TTL is zero, this operation causes a division by zero panic, crashing the server and resulting in a denial-of-service (DoS). The vulnerability requires no authentication or user interaction and can be exploited remotely by sending specially crafted HTTP requests to the proxy server. The CVSS v3.1 base score is 7.5, reflecting a high severity due to the network attack vector, low attack complexity, no privileges or user interaction required, and impact limited to availability (no confidentiality or integrity impact). The issue is fixed in vproxy version 2.4.0. There are no known exploits in the wild at the time of publication, but the simplicity of the attack vector and the direct crash impact make it a significant risk for affected deployments.

For European organizations, the primary impact of this vulnerability is service disruption due to denial-of-service attacks against proxy servers running vulnerable versions of vproxy. Proxy servers are often critical infrastructure components used for traffic routing, security filtering, and access control. A successful DoS attack could interrupt business operations, degrade network performance, and potentially expose organizations to secondary risks if fallback mechanisms are inadequate. While the vulnerability does not directly compromise confidentiality or integrity, the loss of availability can impact user productivity and critical services, especially in sectors relying heavily on proxy infrastructure such as finance, telecommunications, and government. Additionally, organizations using vproxy in multi-tenant or cloud environments may face cascading effects if proxy services are shared among multiple clients. The lack of required authentication means attackers can exploit this remotely without prior access, increasing the threat surface. Given the high CVSS score and ease of exploitation, European entities should prioritize patching to maintain operational continuity.

To mitigate CVE-2025-54581, European organizations should immediately upgrade all vproxy instances to version 2.4.0 or later, where the divide-by-zero flaw is fixed. If upgrading is not immediately feasible, organizations can implement the following practical steps: 1) Deploy network-level filtering to block or rate-limit suspicious Proxy-Authorization headers containing TTL values of zero or malformed usernames resembling the attack pattern (e.g., regex matching '.*-ttl-0'). 2) Enable robust monitoring and alerting on proxy server crashes or restarts to detect potential exploitation attempts early. 3) Use application-layer firewalls or reverse proxies to validate and sanitize HTTP headers before they reach vproxy. 4) Conduct regular vulnerability scanning and penetration testing focused on proxy infrastructure to identify and remediate similar issues proactively. 5) Isolate proxy servers in segmented network zones to limit the blast radius of any DoS attacks. These targeted mitigations complement the essential patching step and help reduce risk exposure during transition periods.