CVE-2017-3870 in Web Security Appliance
Summary
by MITRE
A vulnerability in the URL filtering feature of Cisco AsyncOS Software for Cisco Web Security Appliance (WSA) could allow an unauthenticated, remote attacker to bypass a configured URL filter rule. Affected Products: This vulnerability affects all releases prior to the first fixed release of Cisco AsyncOS Software for Cisco Web Security Appliance (WSA), both virtual and hardware appliances, that are configured with URL filters for email scanning. More Information: CSCvc69700. Known Affected Releases: 8.5.3-069 9.1.1-074 9.1.2-010.
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Analysis
by VulDB Data Team • 12/25/2024
The vulnerability identified as CVE-2017-3870 represents a critical security flaw within the URL filtering mechanism of Cisco AsyncOS Software deployed on Cisco Web Security Appliance systems. This weakness specifically targets the email scanning functionality where URL filter rules are configured to block malicious or unwanted web content. The vulnerability allows unauthenticated remote attackers to circumvent existing URL filter policies, effectively undermining the security controls that organizations have implemented to protect their network infrastructure from web-based threats.
This technical flaw stems from inadequate validation mechanisms within the URL filtering subsystem of the Cisco WSA software. The vulnerability manifests when the system fails to properly evaluate or enforce URL filter rules during email scanning processes, creating a bypass condition that enables attackers to access blocked web resources without proper authentication. The issue affects multiple software releases including versions 8.5.3-069, 9.1.1-074, and 9.1.2-010, indicating it was present across a significant portion of the affected product lifecycle. The vulnerability's impact extends to both virtual and hardware deployments, making it particularly concerning for organizations that may have deployed the software across different infrastructure types.
The operational implications of CVE-2017-3870 are substantial as it directly compromises the integrity of an organization's web security posture. Attackers exploiting this vulnerability could gain access to restricted websites, bypass content filtering policies, and potentially access malicious resources that would normally be blocked by the WSA. This could lead to data exfiltration, malware delivery, or other malicious activities that the security controls were designed to prevent. The vulnerability particularly affects email scanning operations where URL content within emails is analyzed and filtered, creating a potential attack vector that could be exploited to deliver phishing content or access compromised websites that would typically be blocked by the configured security policies.
From a cybersecurity framework perspective, this vulnerability maps to CWE-284 (Improper Access Control) and aligns with ATT&CK techniques related to privilege escalation and defense evasion. The flaw demonstrates a failure in access control mechanisms where unauthorized users can bypass security policies, potentially leading to broader system compromise. Organizations implementing the affected Cisco WSA versions face significant risk as this vulnerability allows remote exploitation without requiring authentication credentials, making it particularly dangerous in environments where network segmentation may not be fully effective. The vulnerability's impact on email scanning capabilities particularly affects enterprise security operations where email is a primary vector for cyber attacks, potentially allowing threat actors to circumvent email content filtering that was specifically designed to prevent such incidents.
Mitigation strategies for CVE-2017-3870 require immediate implementation of software updates and patches provided by Cisco to address the specific URL filtering bypass vulnerability. Organizations should prioritize updating their Cisco WSA appliances to versions that contain the necessary fixes for the affected releases. Network administrators should also implement additional monitoring measures to detect potential exploitation attempts and verify that URL filtering policies are properly enforced. The vulnerability highlights the importance of maintaining current security software versions and implementing robust patch management processes to prevent exploitation of known security flaws. Additionally, organizations should consider implementing network segmentation and additional security controls to limit the potential impact if the vulnerability is successfully exploited, while also conducting thorough security assessments to identify any other potential bypass mechanisms within their web security infrastructure.