CVE-2020-1055 in Windows
Summary
by MITRE
A cross-site-scripting (XSS) vulnerability exists when Active Directory Federation Services (ADFS) does not properly sanitize user inputs, aka 'Microsoft Active Directory Federation Services Cross-Site Scripting Vulnerability'.
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Analysis
by VulDB Data Team • 02/28/2025
The CVE-2020-1055 vulnerability represents a critical cross-site scripting flaw within Microsoft Active Directory Federation Services that fundamentally undermines the security posture of federated authentication environments. This vulnerability resides in the authentication handling mechanisms of ADFS, specifically when processing user-provided inputs that are not adequately sanitized before being rendered in web responses. The flaw allows attackers to inject malicious script code into the authentication flow, potentially compromising user sessions and access credentials within federated environments. The vulnerability affects Microsoft ADFS versions 2016 and 2019, making it particularly concerning given the widespread deployment of these server versions in enterprise environments. The issue stems from insufficient input validation and output encoding practices within the ADFS web interface components that handle user authentication requests, creating an attack surface where malicious actors can manipulate authentication flows through crafted input parameters.
The technical exploitation of this vulnerability occurs through manipulation of input fields within the ADFS authentication process, particularly in areas where user-provided data is reflected back to the browser without proper sanitization. Attackers can craft malicious payloads that, when processed by ADFS, get executed in the context of authenticated users' browsers. This creates a persistent threat vector where session hijacking, credential theft, and unauthorized access to federated resources becomes possible. The vulnerability falls under CWE-79 which specifically addresses Cross-Site Scripting flaws in web applications, and aligns with ATT&CK technique T1566.001 for initial access through spearphishing attachments and links. The flaw is particularly dangerous because it operates at the authentication layer, meaning that successful exploitation can lead to complete compromise of user identities within the federated trust relationship, potentially affecting thousands of users across interconnected systems.
The operational impact of CVE-2020-1055 extends far beyond simple script execution, as it enables attackers to establish persistent access within federated authentication environments where they can monitor, manipulate, or steal authentication tokens. Organizations using ADFS for single sign-on capabilities face significant risk of unauthorized access to cloud services, internal applications, and corporate resources that rely on federated authentication. The vulnerability's exploitation can result in data breaches, privilege escalation, and lateral movement within networks where ADFS serves as a trust boundary. Security teams must recognize that this vulnerability can be leveraged for advanced persistent threats where attackers establish footholds in federated environments and maintain access over extended periods. The risk is amplified in environments where ADFS is integrated with Microsoft 365, Azure, or other cloud services that rely on federated authentication, as successful exploitation could provide attackers with access to sensitive corporate data and infrastructure.
Mitigation strategies for CVE-2020-1055 require immediate implementation of Microsoft security patches and updates, with particular attention to the ADFS server versions affected by this vulnerability. Organizations should implement additional input validation measures at network boundaries and web application firewalls to detect and block malicious payloads attempting to exploit this vulnerability. Regular security assessments of federated authentication environments should include specific testing for XSS vulnerabilities in authentication handlers. Network segmentation and least privilege access controls can help limit the potential damage from successful exploitation, while monitoring for unusual authentication patterns and session behavior can aid in early detection of compromise. Security teams should also implement comprehensive user education programs about recognizing phishing attempts that may leverage this vulnerability, as social engineering remains a primary attack vector for exploiting authentication system flaws. The vulnerability's classification under CWE-79 and its potential for enabling techniques described in ATT&CK matrix T1566.001 emphasize the need for layered defensive approaches that address both technical controls and user awareness training.