CVE-2009-3490 in wget
Summary
by MITRE
GNU Wget before 1.12 does not properly handle a \0 character in a domain name in the Common Name field of an X.509 certificate, which allows man-in-the-middle remote attackers to spoof arbitrary SSL servers via a crafted certificate issued by a legitimate Certification Authority, a related issue to CVE-2009-2408.
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Analysis
by VulDB Data Team • 02/16/2025
The vulnerability described in CVE-2009-3490 represents a critical security flaw in GNU Wget version 1.11 and earlier, where the software fails to properly validate domain names contained within the Common Name field of X.509 certificates. This weakness arises from the improper handling of null characters within domain name specifications, creating a pathway for attackers to execute successful man-in-the-middle attacks against unsuspecting users. The flaw specifically impacts the SSL certificate validation process that occurs during secure HTTP connections, where wget relies on certificate verification to establish trust between the client and server. When a malicious certificate containing a null character in its Common Name field is presented, the vulnerable wget implementation may incorrectly accept it as valid, effectively bypassing the certificate validation mechanism that should prevent such spoofing attempts.
This vulnerability operates at the intersection of certificate validation and string parsing, fundamentally compromising the trust model that SSL/TLS protocols are designed to establish. The technical implementation flaw lies in how wget processes certificate subject names, particularly when encountering null terminators within domain name strings. The issue stems from inadequate input sanitization and validation of certificate fields, allowing malformed certificate data to pass through the verification process. Attackers can exploit this by obtaining a legitimate certificate from a trusted Certification Authority and then modifying the Common Name field to include null characters, thereby creating a certificate that appears valid to the vulnerable wget client while actually allowing the attacker to impersonate any domain. This represents a classic case of insufficient validation leading to certificate forgery and trust exploitation.
The operational impact of this vulnerability extends far beyond simple network communication, as it fundamentally undermines the security assurances provided by SSL/TLS encryption. Users who download files using vulnerable wget versions may unknowingly receive malicious content from attackers who have successfully spoofed legitimate SSL certificates. This vulnerability particularly affects automated systems and scripts that rely on wget for secure file transfers, making it a significant concern for organizations that depend on automated security updates or file retrieval processes. The attack vector is particularly dangerous because it requires no special privileges or complex exploitation techniques beyond obtaining a legitimate certificate and modifying its subject field. The vulnerability essentially allows attackers to establish a false sense of security, as users would believe they are connecting to legitimate servers while actually communicating with malicious intermediaries.
Organizations should implement immediate mitigation strategies including upgrading to GNU Wget version 1.12 or later, which contains the necessary patches to properly handle null characters in certificate domain names. System administrators should also consider implementing additional monitoring and validation mechanisms to detect potential certificate-based attacks, particularly in environments where automated wget usage occurs. The vulnerability aligns with CWE-264, which addresses permissions, privileges, and access controls, and relates to ATT&CK technique T1059.001 for command and scripting interpreter usage, as attackers may leverage this vulnerability to execute malicious payloads through compromised download processes. Additionally, this issue demonstrates the importance of proper input validation and certificate field sanitization, principles that are fundamental to secure coding practices and align with NIST SP 800-53 security controls for system and communications protection.