CVE-2021-34706 in Identity Services Engine
Summary
by MITRE • 10/07/2021
A vulnerability in the web-based management interface of Cisco Identity Services Engine (ISE) could allow an authenticated, remote attacker to access sensitive information or conduct a server-side request forgery (SSRF) attack through an affected device. This vulnerability is due to improper handling of XML External Entity (XXE) entries when parsing certain XML files. An attacker could exploit this vulnerability by uploading a crafted XML file that contains references to external entities. A successful exploit could allow the attacker to retrieve files from the local system, resulting in the disclosure of sensitive information, or cause the web application to perform arbitrary HTTP requests on behalf of the attacker.
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Analysis
by VulDB Data Team • 10/10/2021
The vulnerability identified as CVE-2021-34706 represents a critical security flaw within Cisco Identity Services Engine's web-based management interface, specifically targeting the handling of XML External Entity (XXE) processing. This weakness exists in the parsing mechanisms that manage certain XML files submitted through the administrative portal, creating a pathway for authenticated remote attackers to escalate their privileges and access sensitive system resources. The vulnerability stems from inadequate input validation and sanitization processes that fail to properly restrict external entity references during XML document processing, allowing malicious actors to manipulate the parsing behavior through crafted XML uploads.
The technical exploitation of this vulnerability occurs when an authenticated attacker uploads a specially crafted XML file containing malicious external entity declarations that reference external resources. This XXE implementation enables the attacker to leverage the web application's XML parser to make arbitrary HTTP requests to internal systems or retrieve local files from the server's filesystem. The vulnerability is particularly dangerous because it operates within the context of the web application's privileges, potentially allowing access to sensitive configuration files, user credentials, or system information that should remain protected. The attack vector requires only authentication to the management interface, making it accessible to users with legitimate administrative access who may be compromised or malicious actors who have obtained valid credentials.
The operational impact of this vulnerability extends beyond simple information disclosure, as it enables server-side request forgery attacks that can be leveraged for broader network reconnaissance and lateral movement. An attacker could use the SSRF capabilities to probe internal network services, potentially identifying other vulnerable systems or accessing restricted administrative interfaces. The vulnerability's exploitation could lead to complete system compromise, especially when combined with other attack vectors or when the ISE appliance serves as a central authentication hub for network access control. This makes the vulnerability particularly concerning in enterprise environments where ISE appliances are commonly deployed to manage network access policies and user authentication.
Organizations should implement immediate mitigations including disabling XML file upload capabilities where possible, implementing strict input validation for all XML processing, and applying the latest security patches provided by Cisco. The vulnerability aligns with CWE-611 (Improper Restriction of XML External Entity Reference) and maps to ATT&CK technique T1566.002 (Phishing: Spearphishing Attachment) when considering how attackers might obtain initial access, and T1071.004 (Application Layer Protocol: DNS) when executing SSRF attacks. Network segmentation and monitoring for unusual XML processing activities or outbound requests from the ISE appliance should be implemented as additional defensive measures to detect potential exploitation attempts.