CVE-2011-0633 in libwww-perl
Summary
by MITRE
The Net::HTTPS module in libwww-perl (LWP) before 6.00, as used in WWW::Mechanize, LWP::UserAgent, and other products, when running in environments that do not set the If-SSL-Cert-Subject header, does not enable full validation of SSL certificates by default, which allows remote attackers to spoof servers via man-in-the-middle (MITM) attacks involving hostnames that are not properly validated. NOTE: it could be argued that this is a design limitation of the Net::HTTPS API, and separate implementations should be independently assigned CVE identifiers for not working around this limitation. However, because this API was modified within LWP, a single CVE identifier has been assigned.
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Analysis
by VulDB Data Team • 01/18/2025
The vulnerability described in CVE-2011-0633 represents a critical security flaw in the Net::HTTPS module of libwww-perl that affects numerous web scraping and automation tools including WWW::Mechanize and LWP::UserAgent. This issue stems from improper SSL certificate validation mechanisms that create a window for man-in-the-middle attacks. The vulnerability specifically manifests when the underlying environment fails to establish the If-SSL-Cert-Subject header, which is essential for comprehensive certificate validation. The flaw allows attackers to perform successful impersonation of legitimate servers by exploiting the incomplete hostname validation process, thereby undermining the fundamental security guarantees that SSL/TLS protocols are designed to provide.
From a technical perspective, the vulnerability resides in the default behavior of the Net::HTTPS module where SSL certificate validation does not perform full hostname verification when the If-SSL-Cert-Subject header is absent. This creates a scenario where the module accepts certificates that may be valid in terms of their digital signatures but do not properly match the expected server hostname. The underlying mechanism fails to validate that the certificate's subject name matches the target host, allowing attackers to present certificates that are valid but not intended for the target server. This design limitation specifically affects the SSL certificate validation process and represents a clear violation of proper cryptographic protocol implementation standards. The vulnerability directly maps to CWE-295 which addresses improper certificate validation and CWE-310 which covers cryptographic issues related to key management and validation.
The operational impact of this vulnerability is severe and far-reaching across multiple attack vectors and threat scenarios. Remote attackers can exploit this weakness to conduct successful man-in-the-middle attacks by presenting fraudulent SSL certificates that appear valid to the vulnerable applications. This enables them to intercept, modify, or redirect network traffic between clients and servers without detection. The implications extend beyond simple data interception to include potential credential theft, session hijacking, and complete compromise of sensitive communications. Applications using vulnerable versions of libwww-perl become susceptible to attacks that can compromise user privacy, data integrity, and system security. This vulnerability particularly affects automated web scraping tools, web crawlers, and any application that relies on HTTP/HTTPS communication with external services. The threat landscape is further complicated by the fact that this vulnerability can be exploited silently, making detection difficult for system administrators and security teams.
Mitigation strategies for CVE-2011-0633 require immediate action to upgrade affected systems and implement proper security controls. The primary and most effective mitigation is to upgrade to libwww-perl version 6.00 or later, which contains the necessary fixes for proper SSL certificate validation. Organizations should also implement additional security layers including explicit hostname verification in their application code, deployment of certificate pinning mechanisms, and regular security audits of their web automation tools. Network-level protections such as SSL/TLS inspection and monitoring for suspicious certificate patterns should be implemented. Security teams should also consider implementing certificate transparency monitoring and establish procedures for regular vulnerability assessments of their perl-based web applications. The ATT&CK framework categorizes this vulnerability under T1573 which deals with Encrypted Channel Creation, and T1046 which addresses Network Service Scanning, highlighting the need for comprehensive network security monitoring and endpoint protection. Additionally, organizations should ensure that their security policies mandate the use of validated SSL certificates and proper certificate management practices to prevent exploitation of such vulnerabilities in their infrastructure.