CVE-2015-8597 in ProxySG
Summary
by MITRE
Open redirect vulnerability in Blue Coat ProxySG 6.5 before 6.5.8.8 and 6.6 and Advanced Secure Gateway (ASG) 6.6 might allow remote attackers to redirect users to arbitrary web sites and conduct phishing attacks via a base64-encoded URL in conjunction with a "clear text" one in a coaching page, as demonstrated by "http://www.%humbug-URL%.local/bluecoat-splash-API?%BASE64-URL%."
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Analysis
by VulDB Data Team • 07/02/2022
The CVE-2015-8597 vulnerability represents a critical open redirect flaw in Blue Coat ProxySG and Advanced Secure Gateway appliances, affecting versions prior to 6.5.8.8 and 6.6. This vulnerability stems from inadequate input validation within the proxy appliance's handling of URL parameters, specifically when processing base64-encoded URLs in conjunction with clear text URLs within coaching pages. The flaw allows malicious actors to craft deceptive web requests that can redirect unsuspecting users to attacker-controlled domains, exploiting the trust relationship between the proxy appliance and end users. The vulnerability is particularly dangerous because it leverages the legitimate functionality of the proxy appliance's splash page and coaching mechanisms, making the redirection appear authentic to users who expect to see legitimate authentication or warning pages.
The technical implementation of this vulnerability occurs within the proxy appliance's URL parsing and redirection logic where base64-encoded URLs are processed without proper sanitization or validation. When a user accesses a web resource that triggers the appliance's coaching page functionality, the system fails to adequately verify the legitimacy of the base64-encoded URL parameter before executing a redirect operation. This allows attackers to embed malicious URLs within the base64-encoded portion of the request, which are then decoded and executed as redirect targets. The vulnerability specifically manifests when the appliance processes requests containing the pattern described in the CVE, where the base64-encoded URL is embedded within a larger URL structure that includes clear text components. This creates a scenario where the appliance's redirect functionality can be manipulated to point to any arbitrary destination, bypassing the normal security controls that should prevent such redirections.
The operational impact of this vulnerability extends beyond simple phishing attacks to encompass a broad range of malicious activities that can exploit the trust relationship between users and the proxy appliance. Attackers can leverage this vulnerability to conduct sophisticated phishing campaigns where users are redirected to carefully crafted malicious websites that mimic legitimate corporate or service provider portals. The vulnerability also enables credential harvesting attacks, where users are redirected to attacker-controlled sites designed to capture authentication credentials. Additionally, the flaw can be used to deliver malware through drive-by download scenarios, where users are redirected to malicious sites that automatically attempt to install harmful software on their systems. The sophistication of the attack vector, which combines base64 encoding with clear text URL manipulation, makes this vulnerability particularly challenging to detect and mitigate through traditional security controls.
Organizations affected by CVE-2015-8597 should implement immediate mitigations including firmware updates to versions 6.5.8.8 or 6.6, which contain the necessary patches to address the input validation issues. Network administrators should also consider implementing additional security controls such as URL filtering rules that specifically block requests containing base64-encoded parameters in the context of proxy appliance redirects. The vulnerability aligns with CWE-601 open redirect vulnerability classification and maps to several ATT&CK techniques including T1566 phishing and T1071 application layer protocol for command and control communications. Organizations should also consider implementing user education programs to help users recognize potential phishing attempts, as the vulnerability exploits human factors in addition to technical weaknesses. Regular security assessments and penetration testing should be conducted to identify similar vulnerabilities in other network infrastructure components, as this type of open redirect vulnerability is commonly found in web applications and network appliances. The remediation process should include comprehensive testing of the patched firmware to ensure that legitimate proxy functionality remains intact while the vulnerability is properly addressed.