CVE-2006-5467 in Ruby
Summary
by MITRE
The cgi.rb CGI library for Ruby 1.8 allows remote attackers to cause a denial of service (infinite loop and CPU consumption) via an HTTP request with a multipart MIME body that contains an invalid boundary specifier, as demonstrated using a specifier that begins with a "-" instead of "--" and contains an inconsistent ID.
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Analysis
by VulDB Data Team • 04/25/2026
The vulnerability described in CVE-2006-5467 represents a critical denial of service weakness within the cgi.rb CGI library for Ruby 1.8 systems. This flaw specifically targets the handling of multipart MIME bodies in HTTP requests, creating a condition where maliciously crafted requests can trigger infinite loops and excessive CPU consumption. The vulnerability stems from the library's insufficient validation of boundary specifiers used in multipart form data processing, which forms a fundamental part of web application communication protocols.
The technical implementation of this vulnerability occurs when the cgi.rb library processes HTTP requests containing multipart MIME content with malformed boundary identifiers. Specifically, when a boundary specifier begins with a single hyphen "-" instead of the standard double hyphen "--" required by RFC 1341 and RFC 2046 standards for multipart content, the library enters an infinite loop during parsing operations. Additionally, when these invalid boundaries contain inconsistent identifiers, the parsing algorithm becomes trapped in continuous iteration patterns that consume system resources without termination. This behavior directly violates the expected processing semantics for MIME boundary handling as defined in the relevant internet standards.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise entire web application systems. Attackers can exploit this weakness by crafting HTTP requests with malicious multipart content that causes target Ruby applications to consume excessive CPU cycles indefinitely. The infinite loop condition can lead to complete system unresponsiveness, particularly in environments where multiple concurrent requests are processed, potentially affecting other legitimate users and services. This type of resource exhaustion attack aligns with attack techniques documented in the MITRE ATT&CK framework under the resource exhaustion category, specifically targeting application-level vulnerabilities that can be exploited through web interfaces.
Systems affected by this vulnerability include any Ruby 1.8 applications that utilize the cgi.rb library for processing multipart form data, particularly web applications handling file uploads or complex form submissions. The vulnerability affects both standalone Ruby applications and those integrated within web servers like Apache or Nginx through mod_ruby or similar modules. Organizations running legacy Ruby 1.8 environments are particularly at risk since this version reached end-of-life status and no longer receives security updates. The flaw represents a classic example of improper input validation as classified by CWE-20, which specifically addresses weaknesses in input validation and parsing of structured data formats.
Mitigation strategies for this vulnerability require immediate action including upgrading to newer Ruby versions where this parsing issue has been resolved, implementing request rate limiting and resource monitoring to detect abnormal CPU usage patterns, and deploying application firewalls or web application firewalls that can identify and block malformed multipart requests. The most effective long-term solution involves migrating away from vulnerable Ruby 1.8 versions to supported releases that include proper boundary validation and error handling for MIME parsing operations. Additionally, organizations should implement comprehensive logging and monitoring to detect unusual processing patterns that might indicate exploitation attempts, as this vulnerability can be used in distributed denial of service attacks when combined with multiple target systems.