FAKE CERTIFICATE EXPOSED: How A Misconfigured SSL Renewal On A UK Govt Supplier Subdomain Opens The Door To Data Interception + Video

Introduction:

A misconfigured SSL/TLS setup on a critical subdomain of a major UK Government supplier has been renewed for 12 months, actively exposing a fake digital certificate. This inconsistency across servers creates a serious security gap where attackers can intercept data, disrupt services, and erode public trust in national infrastructure—potentially jeopardising billion-pound contracts and enabling undetected man-in-the-middle attacks.

Learning Objectives:

Identify SSL/TLS misconfigurations and certificate inconsistencies across multiple servers.
Use Linux and Windows command-line tools to detect fake or mismatched certificates.
Implement server‑side hardening, HSTS, certificate pinning, and automated renewal audits to prevent data interception.

You Should Know:

Understanding the SSL/TLS Misconfiguration Risk – Step‑by‑Step Certificate Chain Validation

A fake certificate arises when one server presents a valid, trusted certificate while another server on the same subdomain presents an expired, self‑signed, or incorrectly renewed certificate. Attackers can exploit this inconsistency to bypass encryption, perform session hijacking, or launch phishing campaigns that mimic the legitimate service.

Step‑by‑step guide to verify certificate consistency across servers:

Step 1: Resolve all IP addresses behind the target subdomain (e.g., api.gov-supplier.example). Use `dig` or nslookup:
```
dig +short api.gov-supplier.example
nslookup api.gov-supplier.example
```

Step 2: For each IP, retrieve the SSL certificate details using OpenSSL (Linux/macOS/WSL):

openssl s_client -connect 192.0.2.10:443 -servername api.gov-supplier.example -showcerts </dev/null 2>/dev/null | openssl x509 -text -noout

Step 3: Compare key fields across all IPs: issuer, subject, validity dates, and public key fingerprint. Any mismatch indicates a misconfiguration.

Step 4: On Windows (PowerShell), use the `Test-NetConnection` and .NET’s System.Net.Security.SslStream:

[System.Net.ServicePointManager]::ServerCertificateValidationCallback = {$true}
$req = [System.Net.HttpWebRequest]::Create("https://api.gov-supplier.example")
$req.GetResponse() | Out-Null
$req.ServicePoint.Certificate | Format-List

Detecting Fake Certificates with OpenSSL and Specialised Tools

Attackers actively scan for such inconsistencies. You can replicate their techniques using free, open‑source tools.

Step‑by‑step detection using `testssl.sh` (Linux/macOS):

Step 1: Clone the repository and run against the subdomain:

git clone https://github.com/drwetter/testssl.sh.git
cd testssl.sh
./testssl.sh --certificate api.gov-supplier.example

Step 2: Look for warnings like “Multiple certificates seen” or “Different certificate on other IP”.

Step 3: Use `sslscan` for a quick overview:

sslscan --no-failed api.gov-supplier.example

Step 4: On Windows, use `certlm.msc` (Local Machine Certificates) to view any cached or unexpected certs, or run `openssl.exe` via WSL or standalone binaries.

For automated monitoring, script the check using `bash` or `PowerShell` and alert on any change in certificate fingerprints.

Server‑Side Inconsistency Testing – Finding the Weakest Link

The UK Government supplier example shows that one server may have a legitimate certificate, while another (often a staging, backup, or misconfigured edge server) presents a fake certificate renewed for 12 months. This long validity window amplifies the risk.

Step‑by‑step to map and test all endpoints:

Step 1: Enumerate all A/AAAA records and CDN endpoints using dnsrecon:
```
dnsrecon -d gov-supplier.example -t aaaa
```

Step 2: For each discovered IP, run nmap’s SSL script:

nmap -p 443 --script ssl-cert,ssl-enum-ciphers 192.0.2.10

Step 3: Compare the `ssl-cert` output. Look for “Not valid after” dates and issuer differences.

Step 4: Use `curl` with verbose output to detect certificate warnings:

curl -Iv https://api.gov-supplier.example --resolve api.gov-supplier.example:443:192.0.2.10

Step 5: On Windows, use `Invoke-WebRequest` with `-SkipCertificateCheck` (PowerShell 7+) only for testing, but verify the thumbprint:
```
(Invoke-WebRequest -Uri "https://api.gov-supplier.example" -SkipCertificateCheck).RawContent
```

Mitigating Data Interception Risks – Hardening SSL/TLS Configurations

To prevent fake certificate exploitation, organisations must enforce uniform encryption across all servers, implement strict certificate management, and adopt modern web security headers.

Step‑by‑step mitigation guide:

Step 1: Enforce HTTP Strict Transport Security (HSTS) with preload. Add this header to all server configurations (Apache/Nginx/IIS):
```
Header always set Strict-Transport-Security "max-age=31536000; includeSubDomains; preload"
```
Step 2: Implement Certificate Transparency (CT) monitoring. Use tools like `ct-submit` or services (e.g., Cert Spotter) to alert on unexpected certificates issued for your domains.
Step 3: Automate certificate renewal audits. For Linux, use `certbot` with hooks to validate consistency across all server IPs:
```
certbot renew --deploy-hook "/path/to/check-all-servers.sh"
```

Step 4: On Windows Server, use PowerShell to check all IIS bindings:

Get-ChildItem -Path Cert:\LocalMachine\My | Format-Table Subject, NotAfter, Thumbprint

Step 5: Deploy Certificate Pinning (via HPKP – deprecated, but use Expect-CT or CAA records instead). Add a CAA record to your DNS:
```
example.com. 3600 IN CAA 0 issue "letsencrypt.org"
```

Exploitation and Mitigation of MITM Attacks Using Fake Certificates

A real‑world attacker could position themselves on a network segment between the client and the misconfigured server (e.g., rogue Wi‑Fi, compromised router) and present the fake certificate. Because the fake certificate may still be trusted by some clients (if issued by a public CA or if client ignores warnings), the attacker can decrypt and modify traffic.

Step‑by‑step to demonstrate and then block the attack:

Simulated exploitation (authorised lab only) – Use `mitmproxy` or `Burp Suite` with a self‑signed certificate:
```
mitmproxy --mode transparent --showhost
```
Then configure client to trust the fake CA. Observe decrypted HTTPS traffic.
Mitigation – Enforce mutual TLS (mTLS) for internal APIs. Generate client certificates and validate on the server:
```
ssl_verify_client on;
ssl_client_certificate /etc/nginx/client_ca.crt;
```
Detection – Monitor logs for certificate errors. On Linux, audit `auth.log` for `SSL_accept` errors. On Windows, check `Event Viewer` > `Applications and Services Logs` > `Microsoft` > `Windows` > `CertificateServicesClient` for error events 1003, 1005.

What Undercode Say:

Consistency is the cornerstone of SSL security. A single misconfigured server—especially one renewed for 12 months with a fake certificate—invalidates encryption for the entire subdomain. Attackers only need the weakest link.
Automated, cross‑server validation must become mandatory for government suppliers. Manual checks or single‑server monitoring fail to expose the type of inconsistency highlighted in this UK Government case. CI/CD pipelines should include certificate fingerprint comparison across all production IPs.
Long certificate validity periods are a liability. While 12‑month certificates are standard, they exacerbate the impact of misconfigurations. Shorter lifetimes (e.g., 90 days) combined with automated renewal force frequent validation and reduce the window for fake certificate abuse.

Prediction:

Within the next 12 months, this incident will trigger a mandatory security audit for all UK government suppliers, with specific SSL/TLS consistency testing added to the Cyber Assessment Framework (CAF). We anticipate new contractual requirements for real‑time certificate transparency logging and third‑party penetration testing of every public‑facing IP. Failure to comply will result in contract termination and potential legal liability for data interception damages. Meanwhile, threat actors will actively scan for similar misconfigurations across government and critical national infrastructure (CNI) domains, using fake certificates as a low‑noise persistence mechanism.

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IT/Security Reporter URL:

Reported By: Andy Jenkinson – Hackers Feeds
Extra Hub: Undercode MoN
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