CVE-2003-0540 in Postfix
Summary
by MITRE
The address parser code in Postfix 1.1.12 and earlier allows remote attackers to cause a denial of service (lock) via (1) a malformed envelope address to a local host that would generate a bounce and contains the ".!" string in the MAIL FROM or Errors-To headers, which causes nqmgr to lock up, or (2) via a valid MAIL FROM with a RCPT TO containing a ".!" string, which causes an instance of the SMTP listener to lock up.
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Analysis
by VulDB Data Team • 12/15/2024
The vulnerability described in CVE-2003-0540 represents a critical denial of service flaw within the Postfix mail server software version 1.1.12 and earlier. This weakness specifically targets the address parser functionality that processes email envelope addresses during message delivery operations. The vulnerability stems from insufficient input validation and improper handling of special character sequences within email headers, creating exploitable conditions that can halt normal mail server operations. The flaw affects the core message processing components of Postfix including the nqmgr daemon and SMTP listener processes, which are fundamental to email delivery mechanisms.
The technical implementation of this vulnerability exploits two distinct attack vectors that leverage the presence of the "." is submitted to a local Postfix host, the system generates a bounce message that triggers the nqmgr process to enter an indefinite lock state. This occurs because the address parser fails to properly handle the special character sequence, causing the queue manager to become unresponsive and unable to process subsequent mail queue operations. The second attack vector involves a legitimate MAIL FROM header combined with a RCPT TO header that contains the ".!" string, which causes the SMTP listener process to lock up during the address validation phase. Both attack scenarios demonstrate a classic buffer over-read or parsing error condition where the software does not properly sanitize input before processing.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise entire mail server availability. When the nqmgr daemon locks up, it prevents the processing of new mail messages and the delivery of existing queued messages, effectively creating a mail server outage that can last until manual intervention occurs. Similarly, when the SMTP listener locks up, incoming mail connections are refused and existing connections may hang, preventing legitimate email communication. This vulnerability is particularly dangerous in high-volume email environments where the mail server handles thousands of messages per hour, as the denial of service can quickly cascade into broader network communication failures. Organizations relying on Postfix for email services would experience significant operational disruption, with email delivery delays or complete failures affecting business communications.
The vulnerability aligns with CWE-129, which describes improper validation of input boundaries, and represents a classic example of how malformed input can cause denial of service conditions. From an attack framework perspective, this vulnerability maps to ATT&CK technique T1499.004, which covers network denial of service attacks through resource exhaustion or process locking. The attack requires minimal sophistication and can be executed remotely without authentication, making it particularly dangerous as it can be exploited by anyone with access to the mail server's network interface. The exploitation process involves crafting specific email headers containing the ".!" sequence, which demonstrates a lack of proper input sanitization and validation mechanisms. Organizations should consider implementing network-level protections such as rate limiting and header filtering to mitigate the risk, while the primary solution involves upgrading to Postfix versions that contain proper input validation and error handling for address parsing operations. The vulnerability highlights the importance of robust input validation in mail server software and demonstrates how seemingly innocuous character sequences can cause critical system failures when not properly handled by parsing routines.