Authentication bypass
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.
Noroxi analysis
No Noroxi analysis for this record yet
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We use this product, ask for help- Published
- Apr 27, 2021
- Updated
- Jun 16, 2026
- EPSS
- 83.5% · 100th percentile
- CWE
- CWE-290
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Report tools
Action score
64
This week
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- CVSS
- 39 / 40 · 9.8 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 25 / 30 · 83.5%
CNA vs NVD score
- NVD
- 9.8
- CNA · GitHub_M
- 8.6
- 1.2 point gap
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N
The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.
Affected systems
| Vendor | Product | CPE |
|---|---|---|
| alibaba | nacos | cpe:2.3:a:alibaba:nacos |
Affected versions
NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.
- alibaba nacosbefore 1.4.1
Versions reported by the vendor
Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.
alibaba nacos
- < 1.4.1affected
Package-level exposure
OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.
| Ecosystem | Package | Affected range | Fix |
|---|---|---|---|
| Maven | com.alibaba.nacos:nacos-common | before 1.4.1 | 1.4.1 |
Same product
alibaba: all recordsOther highest-scoring records for the same primary product.
- CVE-2021-29442Authentication bypass50Plan
- CVE-2021-43116An Access Control vulnerability exists in Nacos 2.0.3 in the access prompt page; enter username and password, click on login to capture pack37Monitor
- CVE-2021-44667A Cross Site Scripting (XSS) vulnerability exists in Nacos 2.0.3 in auth/users via the (1) pageSize and (2) pageNo parameters.24Monitor
- CVE-2020-19676Nacos 1.1.4 is affected by: Incorrect Access Control.21Monitor
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
| Product / package | Fixed version | Source |
|---|---|---|
| Maven:com.alibaba.nacos:nacos-common | 1.4.1 | Package registry (OSV) |
Exploit status
Proof of concept available
A public proof of concept or detection signature exists. Exploit knowledge is out there; don't delay patching.
Evidence
- Nuclei detection template ×1
- Proof-of-concept repository on GitHub ×4
Noroxi does not host or link to exploit code. Metasploit module names and Nuclei template ids are shown (names, not code); Exploit-DB entries and PoC repositories are given as counts only.
| Source | Kind | Date |
|---|---|---|
| Nuclei detection template | Nuclei template CVE-2021-29441 | — |
| Proof-of-concept repository on GitHub | stars:0 | 2021-10-05 |
| Proof-of-concept repository on GitHub | stars:2 | 2022-03-15 |
| Proof-of-concept repository on GitHub | stars:0 | 2024-12-04 |
| Proof-of-concept repository on GitHub | stars:0 | 2026-06-25 |
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
- Published
- First PoC+160 d
- TodaySep 30, 2026+1982 d
FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
No credits in the CNA record.
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
No nightly-computed relations.
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
—
Bug bounty scope
The product’s vendor appears in a public program. Matched by name; verify the scope text in the program.
Technical details
Attack conditions
- Anyone who can reach it over the internet can trigger it.
- No account or password is required.
- No user action is required.
- No special conditions are required; it is repeatable.
If successful
- Confidentiality
- high · data can be read
- Integrity
- high · data or configuration can be modified
- Availability
- high · the service can be disrupted
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- High
- Integrity impact
- High
- Availability impact
- High
Weakness class (CWE)
CWE-290 · Authentication Bypass by SpoofingCVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
nvd-primary
Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
Attack patterns (CAPEC)
- Exploitation of Trusted IdentifiersCAPEC-21likelihood: High · High
- Exploiting Trust in ClientCAPEC-22likelihood: High · High
- Creating a Rogue Certification Authority CertificateCAPEC-459likelihood: Medium · Very High
- Web Services API Signature Forgery Leveraging Hash Function Extension WeaknessCAPEC-461High
- Signature SpoofCAPEC-473
- Signature Spoofing by MisrepresentationCAPEC-476likelihood: Low · High
- Session Credential Falsification through PredictionCAPEC-59likelihood: High · High
- Reusing Session IDs (aka Session Replay)CAPEC-60likelihood: High · High
ATT&CK techniques
- Masquerading: Invalid Code SignatureT1036.001
- Access Token ManipulationT1134
- Access Token Manipulation:Token Impersonation/TheftT1134.001
- Steal Application Access TokenT1528
- Steal Web Session CookieT1539
- Use Alternate Authentication Material:Web Session CookieT1550.004
- Subvert Trust Controls: Code SigningT1553.002
- Adversary-in-the-MiddleT1557
Change log
- Fix✗ → ✓
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References
Vendor advisories and official records. Exploit/PoC links are deliberately left out.