CVE-2002-0454 in Qpopper
Summary
by MITRE
Qpopper (aka in.qpopper or popper) 4.0.3 and earlier allows remote attackers to cause a denial of service (CPU consumption) via a very large string, which causes an infinite loop.
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Analysis
by VulDB Data Team • 09/17/2025
The vulnerability identified as CVE-2002-0454 affects Qpopper versions 4.0.3 and earlier, representing a critical denial of service flaw that can be exploited remotely by attackers. This issue specifically impacts the popper daemon, which serves as a POP3 server implementation commonly used in email systems. The vulnerability stems from inadequate input validation within the protocol handling mechanisms, where the software fails to properly process malformed or excessively large data strings. The affected Qpopper implementation, also known as in.qpopper, operates as a daemon process that listens for incoming POP3 connections and processes email retrieval requests from client applications.
The technical flaw manifests when the software receives a particularly large string input that triggers an infinite loop within the processing logic. This occurs because the Qpopper implementation does not implement proper bounds checking or input length validation for incoming protocol data. When such oversized strings are processed, the software enters an endless loop where it continuously processes the malformed input without proper termination conditions. The vulnerability specifically targets the parsing and handling of POP3 protocol commands where string length validation is insufficient, causing the daemon to consume excessive CPU resources. This infinite loop condition effectively prevents the service from processing legitimate requests and can be exploited by remote attackers to exhaust system resources.
The operational impact of this vulnerability extends beyond simple service disruption, as it can be leveraged to perform resource exhaustion attacks against systems running vulnerable Qpopper implementations. Attackers can exploit this weakness by sending specially crafted POP3 commands containing extremely large strings to the affected server, causing the daemon to consume 100% CPU resources and become unresponsive. This denial of service condition affects all users of the POP3 service and can potentially impact email availability for extended periods. The vulnerability is particularly concerning because it requires minimal effort to exploit and can be executed remotely without authentication, making it a preferred target for attackers seeking to disrupt email services. The affected systems include various Unix-like operating systems where Qpopper is installed as the POP3 server implementation.
Mitigation strategies for CVE-2002-0454 focus on immediate software updates and implementation of input validation controls. The primary solution involves upgrading to Qpopper version 4.0.4 or later, where the infinite loop vulnerability has been addressed through proper bounds checking and input validation mechanisms. System administrators should also implement network-level protections such as rate limiting and connection throttling to prevent exploitation attempts. Additionally, monitoring for unusual CPU consumption patterns and implementing intrusion detection systems can help identify exploitation attempts. The vulnerability aligns with CWE-770, which describes allocation of resources without limits or with inadequate limits, and can be categorized under ATT&CK technique T1499.004 for network denial of service attacks. Organizations should also consider implementing firewall rules to restrict POP3 access to trusted networks and establish regular security assessments to identify similar vulnerabilities in other network services.