Executive brief
qmail is a widely used mail transfer agent for routing and delivering email. A vulnerability exists where the software does not limit the number of recipients specified in a single email transaction, allowing an attacker to consume all available system memory. This can lead to a complete system crash or service outage, preventing the organization from sending or receiving legitimate email.
Technical details
The qmail-smtpd component fails to impose a configurable upper bound on the number of RCPT commands processed during a single SMTP session. By sending an unlimited stream of recipient addresses, a remote attacker can trigger dynamic memory allocation that eventually exhausts available swap space or physical memory. This is a resource exhaustion vulnerability (CWE-400) that results in a denial of service. While the vendor argued that system-level resource limits (rlimits) should mitigate this, the lack of application-level bounds allows for trivial exploitation on default configurations.
Affected products
- qmail_project qmail All versions prior to June 1997
Timeline
- 1997-06-01: disclosed: Initial discovery and public discussion by Wietse Venema
- 1997-06-01: advisory: NVD publication date