How should we interpret CVSS severity scores?

CVSS estimates technical severity, but it does not automatically equal business risk. Prioritize using context like internet exposure, asset criticality, known exploitation, and whether compensating controls exist. A Medium CVSS on an exposed production system can be more urgent than a Critical on an isolated non-production host.

Vulnerability Database

Q: What is a Vulnerability (CVE) and why does it matter?

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

Q: What's the difference between a vulnerability, an exploit, and a zero-day?

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. Risk increases sharply when exploitation becomes reliable or widespread.

Q: Why do vulnerabilities keep reappearing in our environment?

Recurring findings usually come from incomplete asset discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host.

Q: How do we prioritize remediation without burning out the team?

Use a repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress so remediation is steady, not reactive.

Q: How can SynScan help reduce vulnerability risk over time?

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358,842

Total vulnerabilities in the database

NATS.io: Adding accounts for just the system account adds auth bypass — github.com/nats-io/nats-server/v2

Authentication Bypass by Primary Weakness

(This advisory is canonically <https://advisories.nats.io/CVE/secnote-2023-01.txt>)

Background

NATS.io is a high performance open source pub-sub distributed communication technology, built for the cloud, on-premise, IoT, and edge computing.

NATS users exist within accounts, and once using accounts, the old authorization block is not applicable.

Problem Description

Without any authorization rules in the nats-server, users can connect without authentication.

Before nats-server 2.2.0, all authentication and authorization rules for a nats-server lived in an "authorization" block, defining users. With nats-server 2.2.0 all users live inside accounts. When using the authorization block, whose syntax predates this, those users will be placed into the implicit global account, "$G". Users inside accounts go into the newer "accounts" block.

If an "accounts" block is defined, in simple deployment scenarios this is often used only to enable client access to the system account. When the only account added is the system account "$SYS", the nats-server would create an implicit user in "$G" and set it as the no_auth_user account, enabling the same "without authentication" logic as without any rules.

This preserved the ability to connect simply, and then add one authenticated login for system access.

But with an "authorization" block, this is wrong. Users exist in the global account, with login rules. And in simple testing, they might still connect fine without administrators seeing that authentication has been disabled.

The blind-spot on our part came from encouraging and documenting a switch to using only "accounts", instead of "authorization".

In the fixed versions, using an "authorization" block will inhibit the implicit creation of a "$G" user and setting it as the no_auth_user target. In unfixed versions, just creating a second account, with no users, will also inhibit this behavior.

Affected versions

NATS Server:

2.2.0 up to and including 2.9.22 and 2.10.1
Fixed with nats-io/nats-server: 2.10.2 and backported to 2.9.23

Workarounds

In the "accounts" block, define a second non-system account, leave it empty.

accounts {
    SYS: {
        users: [
            { user: sysuser, password: makemeasandwich }
        ]
    }
    DUMMY: {}  # for security, before 2.10.2
}
system_account: SYS

Solution

Any one of these:

Upgrade the NATS server to at least 2.10.2 (or 2.9.23)
Or define a dummy account
Or complete the migration of authorization entries to be inside a named account in the "accounts" block

Credits

Problem reported by Alex Herrington.
Addressed publicly in a GitHub Discussion prior to this advisory.

Published: Oct 19, 2023
Updated: Oct 20, 2023
GHSA: GHSA-fr2g-9hjm-wr23
Severity: High
Exploit:
CISA KEV:

No technical information available.

CWEs:

CWE-305

Affected Software
References

Software	From	Fixed in
github.com/nats-io/nats-server/v2	2.2.0	2.9.23
github.com/nats-io/nats-server/v2	2.10.0	2.10.2

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Frequently Asked Questions

What is a Vulnerability (CVE) and why does it matter?

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.

Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.

Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.

SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.