Apache server-info Exposure: 7-Step Deep Analysis of 403 Bypass & Internal Data Leak

About Me

I’m Satyam Pawale, better known in the bug bounty world as @hackersatty. As a dedicated security researcher, I specialize in uncovering complex misconfigurations and information disclosures—especially in web servers and directory services. My toolkit includes Shodan, Burp Suite, custom scripts, and creative reconnaissance techniques. In this article, I’ll guide you through the discovery and exploitation of an Apache server-info Exposure vulnerability, so you can sharpen your own bug bounty skills and help secure critical infrastructure.

2. Introduction

Apache server-info Exposure via a 403 bypass is a critical misconfiguration that can unveil deep internal infrastructure—ranging from module lists and environment variables .

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3. What Are Apache server-info Exposure and server-status?

Apache server-info Exposure HTTP Server provides two administrative modules by default:

• mod_info (/server-info): Reveals server configuration, loaded modules, compiled-in directives, and runtime parameters.

• mod_status (/server-status): Displays live metrics—active requests, worker threads, bytes served, and uptime.

These endpoints are invaluable for administrators but must be strictly restricted (e.g., Require local or IP whitelisting). Left exposed, they become a treasure trove for attackers mapping infrastructure and identifying potential weaknesses.

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4. Path Normalization & Bypass Fundamentals

Web servers normalize incoming paths to apply security rules uniformly. However, path normalization vulnerabilities arise when different components handle slashes inconsistently. A common bypass technique:

1. Expected Denial:

   GET /server-info
→ 403 Forbidden


2. Bypass with Double Slash:

   GET //server-info
→ 200 OK


Some security controls see //server-info as a different resource, failing to apply the 403 rule. By chaining encoding tricks or additional slashes, attackers slip past defenses.

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5. Discovery of the Vulnerability

During routine reconnaissance with automated path enumeration tools, the following sequence occurred:

1. Initial Scan:

   • Tool: Custom Python script iterating common admin paths.

   • Found /server-status and /server-info returned 403 on standard requests.

2. Bypass Attempt:

   curl -I http://target.example.com//server-status
# HTTP/1.1 200 OK


3. Verification:

   • Visiting //server-status in a browser displayed live server metrics.

   • Similarly, //server-info rendered a full HTML page listing configuration details.

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6. Technical Deep Dive: Double-Slash Bypass

6.1 Apache server-info Exposure Configuration Fragment

6.2 Path Normalization Steps

1. Raw Request: //server-info

2. Server Core: Treats leading double slash as a single slash.

3. Authorization Module: Matches against the original request URI (//server-info), skipping the rule that blocks external requests.

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7. Proof of Concept (PoC) Walkthrough

1. Standard Access (Denied):

   curl -i http://target.example.com/server-info
# HTTP/1.1 403 Forbidden


2. Bypass Request (Allowed):

   curl -i http://target.example.com//server-info
# HTTP/1.1 200 OK


3. Retrieve Configuration:

   • Visit http://target.example.com//server-info?config to list full conf.

   • Use ?module=mod_authnz_ldap.c to see LDAP auth directives.

4. Confirm Sensitive Credentials:

   AuthLDAPBindDN "uid=apacheauth,cn=Service Accounts,dc=example,dc=com"
AuthLDAPBindPassword "P@ssw0rd!123"


5. Extract Private IP Ranges:

   • • Over 100 lines of Require ip and Allow from with CIDR blocks like 10.0.0.0/8, 172.16.0.0/12.

   

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8. Exposed Data & Internal Config Details

Through /server-info, the attacker gains:

1. LDAP Authentication Credentials:

   AuthLDAPBindDN "uid=apacheauth,cn=Service Accounts,dc=example,dc=com"
AuthLDAPBindPassword "P@ssw0rd!123"


2. Complete Module List:

   • mod_ssl, mod_dav, mod_proxy, mod_authnz_ldap, mod_log_config, and more.

3. Environment Variables:

   • SERVER_ROOT, HTTPD_ROOT, MPM_WORKER, and custom site-specific vars.

4. Private & Public IP Ranges:

   10.0.0.0/8
172.16.0.0/12
192.168.0.0/16
203.0.113.5
198.51.100.22
…100+ entries


5. Runtime Hooks & VirtualHosts:

   • Active mod_rewrite rules, virtual host configs, SSL cipher suites.

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9. Impact Analysis

• Confidentiality: Attackers see internal topologies, service accounts, and credentials.

• Integrity: Knowledge of modules (e.g., mod_proxy) enables targeted CVE chaining.

• Availability: Although read-only, leaked DoS‐vulnerable modules (e.g., mod_dav) could be exploited.

• Compliance: Violates GDPR/PCI-DSS by exposing sensitive configuration and creds.

• Attack Chains:

  1. Use AuthLDAPBindDN to bind and enumerate directory.

  2. Identify vulnerable modules (e.g., mod_authnz_ldap CVE-2018-1312).

  3. Mount DoS or RCE attacks based on leaked module versions.

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10. Mitigation & Hardening Strategies

1. Disable Unused Modules: Remove mod_info and mod_status from production.

2. Strict Access Controls:

   <LocationMatch "^/server-(info|status)">
Require ip 127.0.0.1 ::1
</LocationMatch>


3. Path Normalization Fixes:

   • Upgrade to Apache server-info Exposure  ≥2.4.50 where double-slash handling is hardened.

   • Add WAF rules to block // sequences.

4. Credential Security: Move LDAP bind credentials to a secure vault—never in plaintext.

5. Regular Audits & Pen Tests: Include bypass scenarios in automated scans.

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11. Broader Security Lessons

• Assume All Endpoints Are Public: Test with modified URIs (//, ..;, URL-encoding).

• Defense in Depth: Even if modules are enabled, restrict them at the network perimeter.

• Secret Management: Hardening is only as strong as your secret storage.

• Monitor for Anomalies: Alert on requests containing suspicious patterns (//server-).

11. External Resources & Further Reading

• Apache HTTP Server Documentation – mod_info

• Apache server-info Exposure HTTP Server Documentation – mod_status

• Apache server-info Exposure HTTP Server Security Tips

• RFC 7230 – Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing

• CVE-2018-1312 – mod_authnz_ldap Information Disclosure

• OWASP Testing Guide – API Security

• Mitre ATT&CK – Network Service Discovery

13. Conclusion

The Apache server-info Exposure vulnerability demonstrates how a seemingly minor path-normalization issue can compromise an entire web server’s security posture. Attackers can bypass 403 restrictions, harvest sensitive credentials, map private networks, and identify vulnerable modules—paving the way for lateral movement and targeted exploits. By understanding the mechanics of double-slash bypass, continuously auditing server configurations, and enforcing strict access controls, organizations can defend against such high-impact misconfigurations.

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14. Final Thoughts: Other Bug Bounty Blogs

Google Dorking remains a powerful reconnaissance technique in modern bug bounty methodology. With the right mindset and crafted queries, it’s possible to uncover sensitive files, misconfigurations, credentials, and more—without sending a single request to the server. This makes it especially useful for stealthy or scope-sensitive bug bounty programs.

Remember: always stay within scope, validate what you find, and follow responsible disclosure guidelines.

Keep exploring. Keep hunting.