CVE-2008-3068 in Publisher
Summary
by MITRE
Microsoft Crypto API 5.131.2600.2180 through 6.0, as used in Outlook, Windows Live Mail, and Office 2007, performs Certificate Revocation List (CRL) checks by using an arbitrary URL from a certificate embedded in a (1) S/MIME e-mail message or (2) signed document, which allows remote attackers to obtain reading times and IP addresses of recipients, and port-scan results, via a crafted certificate with an Authority Information Access (AIA) extension.
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Analysis
by VulDB Data Team • 08/08/2019
The vulnerability described in CVE-2008-3068 represents a critical security flaw in Microsoft's Crypto API implementation that affects multiple Microsoft products including Outlook, Windows Live Mail, and Office 2007. This vulnerability stems from the improper handling of Certificate Revocation List (CRL) checks, where the system automatically retrieves CRL information from URLs specified within certificate extensions without proper validation or user consent. The flaw specifically manifests when processing S/MIME email messages or signed documents that contain certificates with Authority Information Access (AIA) extensions, which are designed to provide information about how to access certificate authorities and related services. The vulnerability is categorized under CWE-693, which deals with protection mechanism weaknesses, and aligns with ATT&CK technique T1566 related to spearphishing attacks that leverage certificate-based mechanisms.
The technical exploitation of this vulnerability occurs when a malicious actor crafts a specially designed certificate containing an AIA extension that points to a controlled server or network resource. When a victim's email client processes this certificate during S/MIME validation, the Crypto API automatically attempts to retrieve the CRL from the specified URL without any user interaction or security verification. This automatic retrieval process enables attackers to gather significant information about the recipient including their IP address, the timing of when the email was opened, and potentially even port scanning information from the network infrastructure. The vulnerability essentially creates a covert channel through which attackers can perform reconnaissance activities and gather intelligence about targets, making it particularly dangerous for threat actors seeking to map network infrastructure or identify active users within organizations.
The operational impact of this vulnerability extends beyond simple information gathering, as it fundamentally undermines the security model of email encryption and digital signatures. Organizations using affected Microsoft products become vulnerable to passive reconnaissance attacks where adversaries can map email recipient networks, identify active systems, and potentially correlate this information with other attack vectors. The vulnerability affects both email clients and document signing processes, creating multiple attack surfaces within enterprise environments where sensitive documents are frequently signed and shared. This weakness particularly impacts organizations that rely heavily on S/MIME encryption for secure communications, as it effectively nullifies the privacy protections that should be provided by digital signatures and certificate validation mechanisms. The automatic nature of the CRL retrieval process means that users cannot be warned about potentially malicious certificate extensions, making this vulnerability particularly insidious and difficult to detect.
Mitigation strategies for this vulnerability require immediate implementation of security patches provided by Microsoft, as the flaw exists in the core Crypto API functionality that cannot be easily worked around through configuration changes. Organizations should implement network-level controls to block access to known malicious URLs and monitor for unusual CRL retrieval patterns that might indicate exploitation attempts. Security teams should also consider implementing email filtering rules that reject messages containing certificates with suspicious AIA extensions or that reference external domains. The vulnerability highlights the importance of proper certificate validation practices and demonstrates how seemingly benign certificate extensions can be weaponized for reconnaissance purposes. Additionally, organizations should review their email security policies to ensure that users are not automatically trusting certificates from untrusted sources, and consider implementing more restrictive certificate validation policies that require explicit user approval for certificate chain validation processes. This vulnerability serves as a reminder of the critical importance of secure certificate handling in cryptographic systems and the potential for seemingly minor implementation flaws to create significant security risks.