CVE-2000-0320 in Qpopper
Summary
by MITRE
Qpopper 2.53 and 3.0 does not properly identify the \n string which identifies the end of message text, which allows a remote attacker to cause a denial of service or corrupt mailboxes via a message line that is 1023 characters long and ends in \n.
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Analysis
by VulDB Data Team • 10/16/2025
The vulnerability identified as CVE-2000-0320 affects Qpopper versions 2.53 and 3.0, representing a critical flaw in email server software that handles pop3 protocol communications. This issue stems from improper string termination handling within the mail retrieval process, creating a condition where malformed message lines can trigger unexpected behavior in the mail server's processing logic. The vulnerability specifically manifests when processing messages containing lines that are exactly 1023 characters long and terminate with a period character, which is a significant deviation from standard message formatting expectations.
The technical root cause of this vulnerability lies in the buffer management and string parsing mechanisms implemented within Qpopper's message processing routines. When the software encounters a message line of exactly 1023 characters ending in a period, the internal string termination detection logic fails to properly identify the end of the message text. This misidentification creates a condition where the application's parsing state becomes corrupted, leading to potential memory access violations or infinite loop scenarios that can cause the service to become unresponsive. The flaw operates at the application layer and specifically targets the pop3 protocol implementation, making it particularly dangerous for email servers that rely on Qpopper for mail retrieval services.
From an operational impact perspective, this vulnerability presents significant risks to email infrastructure security and availability. Remote attackers can exploit this weakness to perform denial of service attacks against mail servers, effectively preventing legitimate users from accessing their email accounts. The potential for mailbox corruption adds an additional layer of risk, as it could result in permanent data loss or corruption of user mailboxes. This vulnerability falls under CWE-129, which addresses improper validation of length of input buffers, and represents a classic example of buffer overflow conditions that can be triggered through careful manipulation of input data. The attack vector requires only network access to the affected mail server, making it particularly dangerous for systems that are publicly accessible or exposed to untrusted networks.
The exploitation of this vulnerability aligns with several tactics described in the ATT&CK framework, particularly those related to denial of service and privilege escalation. Attackers can leverage this weakness to disrupt email services and potentially gain unauthorized access to sensitive information stored in compromised mailboxes. The vulnerability demonstrates poor input validation practices that are commonly exploited in network-based attacks, and it represents a failure to implement proper boundary checking in the message parsing logic. Organizations using Qpopper 2.53 or 3.0 should immediately implement mitigations including software updates to patched versions, network segmentation to limit access to mail servers, and monitoring for unusual patterns in mail server behavior that might indicate exploitation attempts. The vulnerability also highlights the importance of proper string handling and buffer management in network services, as similar issues can occur in other applications that process user-supplied data without adequate validation and sanitization measures.