CVE-2007-0451 in SpamAssassin
Summary
by MITRE
Apache SpamAssassin before 3.1.8 allows remote attackers to cause a denial of service via long URLs in malformed HTML, which triggers "massive memory usage."
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Analysis
by VulDB Data Team • 06/14/2025
Apache SpamAssassin version 3.1.7 and earlier contains a vulnerability that enables remote attackers to induce a denial of service condition through the exploitation of malformed HTML content containing excessively long URLs. This flaw resides in the HTML parsing mechanism where the system fails to properly handle URL length limitations during content analysis. The vulnerability specifically manifests when SpamAssassin processes HTML emails containing URLs that exceed normal parameter limits, causing the application to consume excessive memory resources during the parsing phase. The root cause can be traced to inadequate input validation and resource management within the HTML content processor, which does not implement proper bounds checking on URL lengths. This issue falls under the category of resource exhaustion vulnerabilities and aligns with CWE-400, which addresses unspecified resource exhaustion conditions. The operational impact of this vulnerability is significant as it allows attackers to consume system resources proportional to the length of the malicious URL, potentially leading to system instability, application crashes, or complete service unavailability. Attackers can craft malicious emails with URLs of thousands or even millions of characters, causing the SpamAssassin daemon to allocate excessive memory, ultimately resulting in a denial of service condition that affects legitimate email processing. The vulnerability affects the core functionality of SpamAssassin as a mail filtering system, making it particularly dangerous in enterprise environments where email services are critical. The memory consumption pattern follows a predictable exponential growth curve, where each additional character in the URL length contributes disproportionately to memory allocation. This behavior creates a scenario where a single malicious email can trigger a cascade of memory allocation requests that exhaust available system resources. The attack vector is straightforward and requires minimal technical expertise, as it only necessitates sending an email with a malformed HTML structure containing an excessively long URL. The vulnerability demonstrates a clear weakness in the application's defensive programming practices and input sanitization mechanisms, representing a classic example of insufficient resource management. Organizations relying on SpamAssassin for email security are particularly at risk as this vulnerability can be exploited to disrupt email services without requiring elevated privileges or specialized knowledge. The issue is consistent with ATT&CK technique T1499.004, which covers network denial of service attacks through resource exhaustion, and T1566.001, covering spearphishing with a malicious attachment, as the malicious email would contain the crafted HTML content. Mitigation strategies include implementing URL length restrictions within SpamAssassin configuration, upgrading to version 3.1.8 or later where this vulnerability has been addressed, and deploying additional network-level protections to filter out suspicious email content before it reaches the SpamAssassin processing layer. Network administrators should also consider implementing rate limiting and memory monitoring mechanisms to detect and prevent exploitation attempts. The vulnerability highlights the importance of proper input validation and resource management in security applications, particularly those handling untrusted data from external sources. Organizations should also implement comprehensive logging and monitoring to detect unusual memory consumption patterns that may indicate exploitation attempts. Regular security assessments and vulnerability scanning should include checks for outdated SpamAssassin versions to prevent exploitation of this and similar historical vulnerabilities.