Authentication Bypass

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

not scored

EPSS

• CVE-2021-29441: 83.25% estimated exploitation activity in the next 30 days; percentile 99.68 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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: However the following one gets accepted by using the Nacos-Server user-agent header: Impact This issue may allow any user to carry out any administrative tasks on the Nacos server.

Published by the source

27 Apr 2021, 20:09 UTC

Last modified by the source

1 Feb 2023, 05:05 UTC

Source last checked

26 Oct 2026, 16:06 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-36hp-jr8h-556f

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# Patch Next advisory brief: CVE-2021-29441

Advisory: Authentication Bypass
IDs: CVE-2021-29441, GHSA-36hp-jr8h-556f
Record: https://patchnext.com/advisories/cve-2021-29441 (revision 1, source checked 26 Oct 2026, 16:06 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Unrated
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: com.alibaba.nacos:nacos-common 1.4.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven com.alibaba.nacos:nacos-common: affected < 1.4.1; fixed in 1.4.1

## Suggested inspection (read-only)
- Maven com.alibaba.nacos:nacos-common: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on com.alibaba.nacos:nacos-common.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-36hp-jr8h-556f (GitHub-reviewed advisory GHSA-36hp-jr8h-556f lists affected ranges: Maven com.alibaba.nacos:nacos-common >=0 <1.4.1)

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