CVE-2023-27378: F5 BIG-IP Access Policy Manager XSS Flaw

CVE-2023-27378 Overview

CVE-2023-27378 is a reflected cross-site scripting (XSS) vulnerability affecting multiple pages within the F5 BIG-IP Configuration utility. This web application vulnerability allows attackers to inject malicious JavaScript code that executes in the context of the currently logged-in user's browser session. The vulnerability affects a broad range of F5 BIG-IP product modules, making it a significant concern for organizations relying on F5 infrastructure for application delivery and security.

Reflected XSS vulnerabilities occur when user-supplied input is immediately returned by the web application without proper sanitization or encoding, enabling attackers to craft malicious URLs that execute arbitrary scripts when accessed by authenticated administrators.

Critical Impact

Successful exploitation allows attackers to hijack authenticated administrator sessions, steal session cookies, modify BIG-IP configurations, or perform actions on behalf of privileged users managing critical network infrastructure.

Affected Products

• F5 BIG-IP Access Policy Manager
• F5 BIG-IP Advanced Firewall Manager
• F5 BIG-IP Advanced Web Application Firewall
• F5 BIG-IP Analytics
• F5 BIG-IP Application Acceleration Manager
• F5 BIG-IP Application Security Manager
• F5 BIG-IP Application Visibility and Reporting
• F5 BIG-IP Carrier-Grade NAT
• F5 BIG-IP DDoS Hybrid Defender
• F5 BIG-IP Domain Name System
• F5 BIG-IP Edge Gateway
• F5 BIG-IP Fraud Protection Service
• F5 BIG-IP Global Traffic Manager
• F5 BIG-IP Link Controller
• F5 BIG-IP Local Traffic Manager
• F5 BIG-IP Policy Enforcement Manager
• F5 BIG-IP SSL Orchestrator
• F5 BIG-IP WebAccelerator
• F5 BIG-IP WebSafe

Discovery Timeline

• May 3, 2023 - CVE-2023-27378 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2023-27378

Vulnerability Analysis

This vulnerability is classified as CWE-79 (Improper Neutralization of Input During Web Page Generation), commonly known as cross-site scripting. The flaw exists in undisclosed pages of the BIG-IP Configuration utility, which is the primary web-based management interface for F5 BIG-IP appliances.

The vulnerability requires user interaction, as the victim must click a malicious link or be redirected to a crafted URL. Once triggered, the malicious script runs with the same privileges as the authenticated user, which in the context of BIG-IP typically means administrative access to critical network infrastructure.

The scope of this vulnerability is particularly concerning given that BIG-IP devices often sit at critical points in enterprise networks, handling load balancing, SSL termination, and application security functions.

Root Cause

The root cause of CVE-2023-27378 is insufficient input validation and output encoding in the BIG-IP Configuration utility's web interface. User-controlled parameters are reflected back to the browser without proper sanitization, allowing specially crafted input containing JavaScript code to be executed in the victim's browser context.

This type of flaw typically occurs when:

• User input from URL parameters, form fields, or HTTP headers is directly included in HTML responses
• The application fails to apply context-appropriate output encoding (HTML entity encoding, JavaScript escaping, etc.)
• Content-Security-Policy headers are absent or improperly configured

Attack Vector

The attack requires network access to the BIG-IP Configuration utility and relies on social engineering to trick an authenticated administrator into clicking a malicious link. A typical attack scenario involves:

1. The attacker crafts a malicious URL containing JavaScript payload in a vulnerable parameter
2. The attacker delivers this URL to a target administrator through phishing emails, instant messages, or compromised websites
3. When the administrator clicks the link while authenticated to the BIG-IP Configuration utility, the malicious JavaScript executes
4. The script can then steal session tokens, capture keystrokes, modify configurations, or redirect the user to malicious sites

Due to the sensitive nature of the vulnerability, specific exploitation details and affected pages have not been publicly disclosed by F5.

Detection Methods for CVE-2023-27378

Indicators of Compromise

• Unusual URL patterns in web server logs containing encoded JavaScript or HTML tags (e.g., <script>, javascript:, onerror=)
• Unexpected administrative actions performed without corresponding user intent or during unusual hours
• Session tokens appearing in HTTP Referer headers to external domains
• Anomalous outbound connections from administrator workstations following BIG-IP management interface access

Detection Strategies

• Implement web application firewall (WAF) rules to detect common XSS payloads in requests to the BIG-IP Configuration utility
• Deploy network monitoring to identify unusual patterns in traffic to and from the management interface
• Enable detailed logging on the BIG-IP Configuration utility and correlate with SIEM solutions for anomaly detection
• Monitor for Content-Security-Policy violation reports if CSP headers are implemented

Monitoring Recommendations

• Configure alerts for multiple failed login attempts followed by successful authentication to the Configuration utility
• Establish baselines for normal administrative activity patterns and alert on deviations
• Monitor browser console errors and CSP violations from management interface sessions
• Review access logs for URL parameters containing suspicious character sequences like %3Cscript, %22onclick, or javascript%3A

How to Mitigate CVE-2023-27378

Immediate Actions Required

• Apply the security patches provided by F5 as outlined in the F5 Security Advisory K000132726
• Restrict network access to the BIG-IP Configuration utility to trusted management networks only
• Educate administrators about the risks of clicking links in emails or messages that point to the BIG-IP management interface
• Review and audit recent administrative actions for any unauthorized changes

Patch Information

F5 has released security updates to address CVE-2023-27378. Organizations should consult the F5 Security Advisory K000132726 for specific version information and patching guidance. Software versions that have reached End of Technical Support (EoTS) are not evaluated and may remain vulnerable.

Workarounds

• Implement strict network segmentation to ensure the Configuration utility is only accessible from dedicated management networks
• Deploy a reverse proxy or WAF in front of the management interface to filter malicious requests
• Enable Content-Security-Policy headers where possible to mitigate the impact of XSS attacks
• Consider disabling web-based management and using CLI or API access with proper authentication controls

# Example: Restrict Configuration utility access to specific management networks
# via F5 BIG-IP TMSH (Traffic Management Shell)
tmsh modify sys httpd allow replace-all-with { 10.0.0.0/8 192.168.1.0/24 }
tmsh save sys config