# How to Audit SSH Server Configurations for Security Vulnerabilities Using the Book of Secret Knowledge

> Audit SSH server configurations for security vulnerabilities using ssh-audit and ssh_scan from The Book of Secret Knowledge. Enhance your server security today.

- Repository: [Michał Ży/the-book-of-secret-knowledge](https://github.com/trimstray/the-book-of-secret-knowledge)
- Tags: how-to-guide
- Published: 2026-02-24

---

**You can audit SSH server configurations for security vulnerabilities using two curated tools from *The Book of Secret Knowledge*: `ssh-audit` for cryptographic analysis and `ssh_scan` for policy compliance checks.**

The *Book of Secret Knowledge* repository by trimstray collects battle-tested open-source utilities for system administrators. Auditing SSH server configurations for security vulnerabilities becomes straightforward when you leverage the `ssh-audit` and `ssh_scan` tools catalogued in the project's [`README.md`](https://github.com/trimstray/the-book-of-secret-knowledge/blob/main/README.md) under the CLI Tools chapter.

## Essential Tools for SSH Security Auditing

The repository highlights two distinct utilities that cover complementary aspects of SSH hardening.

### ssh-audit – Cryptographic Scanner

**`ssh-audit`** performs comprehensive analysis of SSH protocol implementations. According to the source code listing in [`README.md`](https://github.com/trimstray/the-book-of-secret-knowledge/blob/main/README.md), this tool inspects protocol versions, ciphers, MACs, key exchange algorithms, and host-key algorithms to identify deprecated or weak cryptographic primitives.

Run a basic audit against any host:

```bash
ssh-audit example.com

```

For integration with monitoring systems, generate structured output:

```bash
ssh-audit --json example.com > ssh-audit-report.json

```

### ssh_scan – Policy Compliance Checker

**`ssh_scan`** focuses on configuration-level security policies rather than cryptographic details. As documented in the repository's CLI Tools section, this utility validates settings such as `AllowUsers`, `PermitRootLogin`, and `PasswordAuthentication` against security baselines.

Execute a policy scan with:

```bash
ssh_scan -t example.com

```

The `-c` and `-p` flags allow customization of which compliance checks execute against your `sshd_config`.

## Step-by-Step SSH Audit Workflow

Follow this systematic approach to evaluate your SSH posture using the tools from *The Book of Secret Knowledge*:

1. **Install the required utilities**

   ```bash
   # ssh-audit (Python-based)

   python3 -m pip install ssh-audit
   
   # ssh_scan (Go-based binary)

   curl -L https://github.com/mozilla/ssh_scan/releases/latest/download/ssh_scan-linux-amd64 -o /usr/local/bin/ssh_scan
   chmod +x /usr/local/bin/ssh_scan
   ```

2. **Perform cryptographic reconnaissance**

   ```bash
   ssh-audit myserver.example.com
   ```

   Review the output for SSH version banners, supported key exchange algorithms, and cipher suites. Flag any entries marked as deprecated.

3. **Generate machine-readable reports**

   ```bash
   ssh-audit --json myserver.example.com > audit.json
   ```

   JSON output enables automated parsing in CI/CD pipelines.

4. **Validate security policies**

   ```bash
   ssh_scan -t myserver.example.com
   ```

   This checks configuration directives like `PermitRootLogin=no` and `PasswordAuthentication=no`.

5. **Consolidate findings**

   ```bash
   ssh-audit --json myserver.example.com > crypto-audit.json
   ssh_scan -t myserver.example.com -o json >> policy-audit.json
   jq '.' policy-audit.json
   ```

6. **Remediate and restart**

   Edit `/etc/ssh/sshd_config` to disable weak algorithms and enforce strict policies. Apply changes with:

   ```bash
   systemctl restart sshd
   ```

## Analyzing SSH Configuration Output

Understanding the audit results requires parsing both cryptographic strength and configuration compliance.

### Detecting Weak Algorithms

Filter `ssh-audit` output to isolate vulnerable ciphers immediately:

```bash
ssh-audit myserver.example.com | grep -i "weak"

```

Weak algorithms typically include small key sizes or deprecated hash functions that the tool flags automatically.

### Validating Security Policies

Check for dangerous configuration patterns like root login allowance:

```bash
ssh_scan -t myserver.example.com | grep "PermitRootLogin"

```

Violations appear when the server permits direct root access or password authentication, requiring immediate `sshd_config` adjustments.

## Automating Audits with JSON Output

For infrastructure-as-code environments, parse audit results programmatically:

```python
import json
import subprocess
import sys

host = sys.argv[1]
result = subprocess.check_output(["ssh-audit", "--json", host])
data = json.loads(result)

# Flag deprecated ciphers below 128-bit strength

weak_ciphers = [c for c in data["ciphers"] if c["strength"] < 128]
if weak_ciphers:
    print("Critical: Weak ciphers detected:", weak_ciphers)
    sys.exit(1)

```

This approach integrates SSH auditing into deployment gates, preventing servers with vulnerable configurations from reaching production.

## Summary

- **`ssh-audit`** evaluates cryptographic implementations including ciphers, MACs, and key exchange algorithms in [`README.md`](https://github.com/trimstray/the-book-of-secret-knowledge/blob/main/README.md)'s CLI Tools section.
- **`ssh_scan`** validates `sshd_config` policies such as `PermitRootLogin` and `PasswordAuthentication` settings.
- Both tools support **JSON output** (`--json` for ssh-audit, `-o json` for ssh_scan) for automated security pipelines.
- Installation methods vary: `ssh-audit` requires Python pip, while `ssh_scan` distributes pre-compiled Go binaries.
- Remediation involves editing `/etc/ssh/sshd_config` and restarting the SSH service after audit completion.

## Frequently Asked Questions

### What is the difference between ssh-audit and ssh_scan?

**`ssh-audit`** analyzes cryptographic implementations, detecting weak ciphers, deprecated MACs, and protocol version vulnerabilities. **`ssh_scan`** focuses on configuration file compliance, verifying that `sshd_config` directives like `PermitRootLogin=no` and `AllowUsers` restrictions are properly enforced. Use both together for comprehensive coverage.

### Where are these tools documented in the Book of Secret Knowledge?

Both utilities appear in the **CLI Tools** chapter of [`README.md`](https://github.com/trimstray/the-book-of-secret-knowledge/blob/main/README.md). The `ssh-audit` entry details Python installation and cryptographic scanning capabilities, while the `ssh_scan` entry covers Go-based policy compliance checking against Mozilla's security guidelines.

### Can I automate SSH auditing in CI/CD pipelines?

Yes. Both tools support machine-readable output formats. Run `ssh-audit --json` and `ssh_scan -o json` to generate structured data, then parse results with Python or `jq` to fail builds when servers expose weak algorithms or violate security policies.

### How do I remediate weak cipher findings?

Edit `/etc/ssh/sshd_config` to remove vulnerable algorithms from `Ciphers`, `MACs`, and `KexAlgorithms` directives. Add explicit restrictions like `Ciphers chacha20-poly1305@openssh.com,aes256-gcm@openssh.com`. Validate changes with `sshd -t`, then restart the service using `systemctl restart sshd` and re-run the audit to confirm hardening.