CVE-2005-3351 in SpamAssassin
Summary
by MITRE
SpamAssassin 3.0.4 allows attackers to bypass spam detection via an e-mail with a large number of recipients ("To" addresses), which triggers a bus error in Perl.
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Analysis
by VulDB Data Team • 06/29/2025
CVE-2005-3351 represents a critical buffer overflow vulnerability affecting SpamAssassin version 3.0.4 that enables attackers to circumvent spam detection mechanisms through carefully crafted email messages. This vulnerability specifically targets the Perl interpreter's handling of email headers containing an excessive number of recipient addresses in the "To" field, creating a condition that results in a bus error within the Perl runtime environment. The flaw occurs when SpamAssassin processes emails with thousands of recipient addresses, causing the application to crash or behave unpredictably due to improper memory management during header parsing operations.
The technical implementation of this vulnerability stems from inadequate input validation and memory allocation handling within SpamAssassin's email processing routines. When Perl encounters an email message with an excessive number of "To" addresses, the application fails to properly manage memory resources allocated for header processing, leading to stack corruption or memory exhaustion that manifests as a bus error. This type of vulnerability falls under the CWE-121 CWE category for buffer overflow conditions in stack-based buffers, where insufficient bounds checking allows attackers to manipulate memory layout. The vulnerability is particularly dangerous because it operates at the parsing layer of the email processing pipeline, meaning that legitimate spam detection mechanisms are bypassed entirely when the application crashes or becomes unresponsive.
From an operational perspective, this vulnerability creates a significant security risk as attackers can exploit it to deliver spam or malicious content without triggering the intended spam filtering protections. The bus error condition effectively neutralizes SpamAssassin's ability to analyze incoming messages, allowing unwanted emails to pass through the system undetected. Network administrators face the challenge of maintaining spam protection while dealing with potential application instability that could affect legitimate email services. The vulnerability also impacts system availability as the SpamAssassin service may become unresponsive or require manual restart following exploitation attempts.
The attack surface for this vulnerability extends beyond simple spam bypass to include potential denial of service scenarios that could affect email server availability. Attackers can leverage this weakness by sending emails with thousands of recipient addresses to overwhelm the SpamAssassin processing engine, potentially causing cascading failures in email infrastructure. This behavior aligns with ATT&CK technique T1499.004 for network denial of service attacks, where the attacker targets application-level vulnerabilities to disrupt services. Organizations should implement immediate mitigations including upgrading to patched versions of SpamAssassin, implementing email size limits, and establishing rate limiting mechanisms to prevent exploitation attempts. Additionally, monitoring for unusual email processing patterns and implementing proper input validation at the network level can help detect and prevent exploitation attempts before they can cause significant damage to spam filtering capabilities.