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critical·Product Based Web Vulnerabilities·Updated Dec 16, 2023

CVE-2021-29441 Scanner

Detects 'Authentication Bypass' vulnerability in nacos affects v. before 1.4.1.

Est. Time~15 seconds
Scan TypeSingle Scan
Targetsdomain, ipv4, subdomain
CostFree
2.8k
Times Used
continuous scan runs
3.7k
Continuously Checked
assets under CS
0
Vulnerabilities Found
confirmed findings
References
CVECVE-2021-29441
9.8
CVSShigh
Exploitable remotely over the internet · no authentication required.

Nacos is a platform designed for dynamic service discovery and configuration and service management. In Nacos before version 1.4.1, when configured to use authentication (-Dnacos.core.auth.enabled=true) Nacos uses the AuthFilter servlet filter to enforce authentication. This filter has a backdoor that enables Nacos servers to bypass this filter and therefore skip authentication checks. This mechanism relies on the user-agent HTTP header so it can be easily spoofed. This issue may allow any user to carry out any administrative tasks on the Nacos server.

Attack Vector
Network
Privileges Req.
None
User Interaction
None
Affected
nacosby alibaba
< 1.4.1
Updated Aug 21, 2026View on NVD →
Detail

Nacos is a platform specifically designed for dynamic service discovery, configuration, and service management. It is mainly used by developers and system administrators to manage distributed systems and microservices. The platform offers a comprehensive set of features such as service registration, service discovery, dynamic configuration, and DNS resolution. Nacos is compatible with popular cloud platforms like Kubernetes and Docker and provides multi-tenancy support for managing multiple environments like development, staging, and production.

The CVE-2021-29441 vulnerability detected in Nacos before version 1.4.1 is a major security concern for all users. The problem lies with the AuthFilter servlet filter, designed to enforce authentication when configured to use authentication (-Dnacos.core.auth.enabled=true). The filter has a backdoor that Nacos servers can use to bypass it, thereby allowing any user to carry out any administrative task on the Nacos server. The vulnerability is so critical that it can permit remote attackers to carry out a wide range of attacks and compromise sensitive data and resources.

Exploiting this vulnerability can result in a series of consequences, ranging from data theft to hijacking of critical network systems. Attackers can exploit this vulnerability to bypass authentication checks and gain admin access to the Nacos servers. Once they have admin access, they can modify configurations, steal data, inject malware into the system, and even shut down critical production systems. Furthermore, the vulnerability can easily be exploited by attackers to execute remote code execution attacks that can compromise the entire network infrastructure and cause it to fail.

In conclusion, s4e.io provides an excellent platform for learning about vulnerabilities in digital assets. By leveraging their pro features, users can easily and quickly detect any known vulnerability in their network systems and take steps to secure them promptly. Everyone must take this opportunity to protect their digital assets by staying up-to-date with the latest vulnerabilities and securing their network systems with caution.

 

REFERENCES

Solution Advice

Fortunately, there are several precautions that users can take to protect themselves from this vulnerability. Some of the steps that can be taken include:

  • Update Nacos to the latest version immediately.
  • Disable the affected server and rotate all user accounts' passwords.
  • Create a custom filter that detects user-agent HTTP headers that are not valid.
  • Monitor and restrict system logs access as well as user access to sensitive data and resources.
  • Implement Two-Factor Authentication (2FA) on all Nacos servers to mitigate the risk of future attacks.

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