CVE-2023-20886: VMware Workspace ONE UEM Redirect Flaw

CVE-2023-20886 Overview

VMware Workspace ONE UEM console contains an open redirect vulnerability that could allow malicious actors to intercept SAML authentication responses. This flaw enables attackers to redirect victims to malicious sites during the authentication flow, potentially allowing the attacker to capture and replay the victim's SAML response to impersonate legitimate users.

Critical Impact

Attackers can hijack SAML authentication responses, enabling account takeover by impersonating legitimate users in the VMware Workspace ONE UEM console.

Affected Products

• VMware Workspace ONE UEM (multiple versions)

Discovery Timeline

• 2023-10-31 - CVE-2023-20886 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-20886

Vulnerability Analysis

This vulnerability is classified under CWE-601 (URL Redirection to Untrusted Site, also known as Open Redirect). The flaw exists within the VMware Workspace ONE UEM console's URL handling mechanism, specifically in how redirect parameters are processed during SAML-based authentication flows.

The vulnerability allows an attacker to craft a malicious URL that, when accessed by a victim, redirects them to an attacker-controlled server. Because this redirect occurs within the context of SAML authentication, the victim's SAML response—containing authentication assertions—can be intercepted by the attacker.

Root Cause

The root cause is improper validation of URL redirect parameters in the Workspace ONE UEM console. The application fails to adequately verify that redirect URLs point to trusted destinations before performing the redirect operation. This allows attackers to inject arbitrary external URLs into the redirect parameter, which the application then follows without proper sanitization.

Attack Vector

The attack requires network access and user interaction. An attacker crafts a malicious URL containing the Workspace ONE UEM console's legitimate domain with a manipulated redirect parameter pointing to an attacker-controlled server. When a victim clicks this link (typically delivered via phishing), they are initially directed to the legitimate VMware authentication endpoint. However, upon successful authentication, the SAML response is redirected to the attacker's server instead of the legitimate callback URL.

The attacker can then capture the SAML assertion and replay it against the legitimate Workspace ONE UEM console to gain authenticated access as the victim user. This is particularly dangerous in enterprise environments where Workspace ONE UEM manages mobile devices and endpoints across the organization.

Detection Methods for CVE-2023-20886

Indicators of Compromise

• Unusual redirect URLs in authentication logs containing external or unfamiliar domains
• SAML authentication requests with suspicious or unexpected redirect_uri parameters
• Multiple authentication events from different IP addresses for the same user in short time windows
• Failed or duplicate SAML assertion replays in authentication logs

Detection Strategies

• Monitor Workspace ONE UEM console access logs for URLs containing external redirect parameters
• Implement Web Application Firewall (WAF) rules to detect and block requests with suspicious redirect patterns
• Review SAML authentication logs for anomalies in callback URLs or assertion replay attempts
• Correlate user authentication events with geographic or IP-based anomaly detection

Monitoring Recommendations

• Enable verbose logging on the Workspace ONE UEM console for authentication events
• Configure alerts for authentication attempts from new or unusual IP addresses
• Monitor for phishing campaigns targeting your organization that contain Workspace ONE UEM URLs
• Implement SIEM rules to detect open redirect patterns in web traffic logs

How to Mitigate CVE-2023-20886

Immediate Actions Required

• Apply the security patch referenced in VMware Security Advisory VMSA-2023-0025 immediately
• Review authentication logs for any evidence of exploitation prior to patching
• Notify users about potential phishing attempts leveraging this vulnerability
• Consider implementing additional URL validation at the network perimeter

Patch Information

VMware has released security updates to address this vulnerability. Organizations should consult the VMware Security Advisory VMSA-2023-0025 for specific version information and upgrade paths. Apply the vendor-provided patches to all affected Workspace ONE UEM console installations as soon as possible.

Workarounds

• Implement strict URL allowlisting at the WAF level to block redirects to unauthorized domains
• Deploy browser-based phishing protection to warn users of suspicious redirect chains
• Enable multi-factor authentication (MFA) to add an additional layer of protection against SAML replay attacks
• Consider network segmentation to limit exposure of the Workspace ONE UEM console to only authorized networks

# Example WAF rule to block suspicious redirects (generic pattern)
# Adjust for your specific WAF platform
# Block requests with external URLs in redirect parameters
SecRule ARGS:redirect_uri "@rx ^https?://(?!your-trusted-domain\.com)" \
    "id:1001,phase:1,deny,status:403,msg:'Blocked suspicious redirect'"