CVE-2021-3127Network attack vector

Cross-account subject access via import token reuse

Published Mar 16, 2021 · Updated Aug 3, 2024

Incorrect access control in NATS Server 2.x before 2.2.0 allows remote authenticated users to read exported subjects via crafted Import Tokens. The JWT library warns on Import Token binding mismatches instead of rejecting them, allowing a token issued for one account to be reused by another account and applied to subjects beyond the token's intended subject. Exploitation requires an untrusted account that can upload a tampered Account JWT to the Account Server; successful abuse exposes exported subject data across accounts.

CVSS severity7.5
High
EPSS probability1.45%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Incorrect access control in NATS Server 2.x before 2.2.0 allows remote authenticated users to read exported subjects via crafted Import Tokens. The JWT library warns on Import Token binding mismatches instead of rejecting them, allowing a token issued for one account to be reused by another account and applied to subjects beyond the token's intended subject. Exploitation requires an untrusted account that can upload a tampered Account JWT to the Account Server; successful abuse exposes exported subject data across accounts.

The record

CVE
CVE-2021-3127
Published
Mar 16, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-755, T1190
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 16, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.5NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
5.0NVDAV:N/AC:L/Au:N/C:P/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-755Improper Handling of Exceptional Conditions
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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