CVE-2021-29441:Authentication Bypass Vulnerability in Nacos via User-Agent Spoofing

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Nacos versions prior to 1.4.1 contain an authentication bypass vulnerability (CWE-290) that allows attackers to perform unauthorized administrative actions by spoofing a specific User-Agent HTTP header. When Nacos is configured with authentication enabled, the AuthFilter servlet filter contains a backdoor mechanism that permits certain user-agent strings to bypass authentication checks entirely, effectively granting administrative access to unauthenticated users.

Overview

Nacos is a popular platform for dynamic service discovery, configuration management, and service management developed by Alibaba. The vulnerability exists in the authentication mechanism of Nacos when authentication is explicitly enabled using the "-Dnacos.core.auth.enabled=true" configuration. The AuthFilter servlet filter, responsible for enforcing authentication, contains a backdoor that allows requests with specific user-agent HTTP headers to bypass authentication checks completely. Since the bypass mechanism relies solely on the user-agent header, which can be easily spoofed by any client, attackers can exploit this vulnerability to gain unauthorized administrative access to the Nacos server. This could lead to unauthorized configuration changes, service disruption, or data exposure.

Remediation

  1. Update Nacos to version 1.4.1 or later, which addresses this vulnerability.
  2. If immediate updating is not possible, implement network-level controls to restrict access to the Nacos management interfaces.
  3. Monitor for suspicious activities in Nacos logs, particularly focusing on administrative actions.
  4. Consider implementing additional authentication layers, such as API gateways or reverse proxies with strong authentication mechanisms, in front of your Nacos instances.
  5. Audit your Nacos configurations to ensure they haven't been tampered with if you suspect exploitation may have occurred.

References

  1. GitHub Security Advisory: https://github.com/advisories/GHSA-36hp-jr8h-556f
  2. Vulnerability Report: https://github.com/alibaba/nacos/issues/4701
  3. Fix Pull Request: https://github.com/alibaba/nacos/pull/4703

Industry ExposureMost to least
This section illustrates the prevalence of a specific Common Vulnerabilities and Exposures (CVE) across various industries based on customer reports. The ranking displays industries from the most to least affected by this particular vulnerability, offering valuable insight into where this CVE has been most frequently observed. This information can help organizations within these sectors prioritize their security efforts, understand their relative risk exposure compared to their peers, and focus remediation strategies where they are most needed. By understanding the industry-specific impact, organizations can make more informed decisions regarding patching, resource allocation, and overall risk management related to this CVE.

  1. Manufacturing: Low
    Manufacturing
  2. Accommodation & Food Services: Low
    Accommodation & Food Services
  3. Administrative, Support, Waste Management & Remediation Services: Low
    Administrative, Support, Waste Management & Remediation Services
  4. Agriculture, Forestry Fishing & Hunting: Low
    Agriculture, Forestry Fishing & Hunting
  5. Arts, Entertainment & Recreation: Low
    Arts, Entertainment & Recreation
  6. Construction: Low
    Construction
  7. Educational Services: Low
    Educational Services
  8. Finance and Insurance: Low
    Finance and Insurance
  9. Health Care & Social Assistance: Low
    Health Care & Social Assistance
  10. Information: Low
    Information
  11. Management of Companies & Enterprises: Low
    Management of Companies & Enterprises
  12. Mining: Low
    Mining
  13. Other Services (except Public Administration): Low
    Other Services (except Public Administration)
  14. Professional, Scientific, & Technical Services: Low
    Professional, Scientific, & Technical Services
  15. Public Administration: Low
    Public Administration
  16. Real Estate Rental & Leasing: Low
    Real Estate Rental & Leasing
  17. Retail Trade: Low
    Retail Trade
  18. Transportation & Warehousing: Low
    Transportation & Warehousing
  19. Utilities: Low
    Utilities
  20. Wholesale Trade: Low
    Wholesale Trade

Focus on What Matters

  1. See Everything.
  2. Identify True Risk.
  3. Proactively Mitigate Threats.

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