CVE-2019-19381 in OAuth Login
Summary
by MITRE
oauth/oauth2/v1/saml/ in Abacus OAuth Login 2019_01_r4_20191021_0000 before prior to R4 (20.11.2019 Hotfix) allows Reflected Cross Site Scripting (XSS) via an error message.
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Analysis
by VulDB Data Team • 05/11/2025
The vulnerability identified as CVE-2019-19381 affects the Abacus OAuth Login component version 2019_01_r4_20191021_0000 and earlier releases. This security flaw resides within the oauth/oauth2/v1/saml/ endpoint which handles SAML authentication processes. The vulnerability represents a classic reflected cross site scripting issue that occurs when the application fails to properly sanitize user input before incorporating it into error messages displayed to users. This particular implementation flaw affects the SAML authentication flow within the OAuth2 framework, creating a pathway for malicious actors to inject malicious scripts into the authentication process.
The technical exploitation of this vulnerability occurs when an attacker crafts malicious input that gets reflected back in an error message without proper sanitization or encoding. When a victim accesses a specially crafted URL or triggers an error condition through malformed SAML parameters, the application includes the unsanitized input directly into the HTML response. This reflected payload can contain JavaScript code that executes in the victim's browser context, potentially allowing attackers to steal session cookies, perform unauthorized actions, or redirect users to malicious sites. The vulnerability specifically targets the error handling mechanism within the SAML authentication flow, making it particularly dangerous as it can be triggered during legitimate authentication attempts.
The operational impact of this vulnerability extends beyond simple script execution as it can compromise the entire authentication ecosystem. Attackers can leverage this XSS flaw to hijack user sessions, potentially gaining administrative access to systems protected by SAML authentication. The vulnerability affects the integrity of the authentication process itself, undermining trust in the security controls that protect sensitive systems. Organizations using this version of Abacus OAuth Login face significant risk as the flaw can be exploited through various attack vectors including phishing campaigns, social engineering, or direct URL manipulation. The reflected nature of the vulnerability means that attackers do not need to persist malicious code on the server, making detection more challenging and the attack surface broader.
Security mitigations for this vulnerability should focus on implementing proper input validation and output encoding mechanisms throughout the authentication flow. The recommended approach involves sanitizing all user-provided input before incorporating it into error messages or any HTML responses. This includes implementing Content Security Policy headers to limit script execution, encoding special characters in error messages, and ensuring that all authentication endpoints properly validate and sanitize input parameters. Organizations should immediately update to the patched version R4 (20.11.2019 Hotfix) or implement temporary workarounds such as URL filtering and input validation at the network level. This vulnerability aligns with CWE-79 which specifically addresses cross-site scripting flaws, and maps to ATT&CK technique T1059.007 for script injection attacks. The remediation process should include comprehensive testing of all authentication endpoints to ensure that no similar reflected XSS vulnerabilities exist in related components.