What Is the PHPInfo.php.bak Vulnerability?

The phpinfo.php.bak vulnerability occurs when a PHP information disclosure file — typically generated during debugging, migration, or deployment — is left on a web server as an unprotected backup copy. The .bak extension signals that this is a secondary or archived version of phpinfo.php, but most web servers will serve .bak files as plain text unless explicitly configured otherwise.

When an attacker requests https://example.com/phpinfo.php.bak, the server returns the full raw PHP configuration dump, which includes:

• PHP version and compiled-in modules — revealing outdated extensions with known CVEs
• Server API (SAPI) — identifying whether PHP runs as Apache module, CGI, FPM, or CLI
• Database connection strings and credentials — if hard-coded in configuration files accessible from the same document root
• System and OS paths — enabling local file inclusion (LFI) and path traversal attacks
• Open-basedir and safe mode status — confirming whether PHP's filesystem protections are disabled
• Environment variables and $_SERVER data — exposing internal IP addresses, hosting control panel paths, and API keys
• Loaded configuration file paths — pointing directly to php.ini and application config files

The combination of these details gives an attacker a near-complete blueprint of the server environment, dramatically reducing the effort required to craft a targeted exploit chain.

Why the .bak Extension Makes Things Worse

A developer may have deleted phpinfo.php after completing their work, assuming the risk was mitigated. However, the backup file phpinfo.php.bak was never removed. In many cases, the developer also included the original phpinfo.php output inside the .bak file itself, meaning the backup contains both the PHP source code and its rendered configuration data.

This single oversight transforms what should be a routine housekeeping task into a critical information disclosure event that automated scanners detect and exploit within minutes of public exposure.

How Attackers Discover and Exploit Exposed phpinfo.php.bak Files

Automated Reconnaissance at Scale

Attackers do not manually search for phpinfo.php.bak files. The reconnaissance is performed by automated bots and scanning frameworks that crawl the internet continuously. Key tools include:

• Shodan and Censys — search engines that index server banners and HTTP responses, making phpinfo.php.bak files discoverable through simple keyword queries
• Nuclei templates — community-maintained vulnerability scanners with pre-built templates for detecting phpinfo backups and other PHP exposure vectors
• Dirb / Gobuster / ffuf — directory brute-force tools that iterate through common backup file names across thousands of targets
• ZenMap and custom Python scripts — allowing attackers to run mass scans across entire IP ranges or ASNs in a single session

The Exploitation Chain

Once a phpinfo.php.bak file is discovered, the exploitation path typically follows this sequence:

1. Information gathering — extract PHP version, loaded modules, OS, and paths from the exposed configuration
2. Vulnerability mapping — cross-reference the PHP version and module list against the National Vulnerability Database (NVD) and exploit-db to identify known CVEs
3. Local file inclusion setup — use disclosed paths to construct LFI payloads that traverse to sensitive system files such as /etc/passwd, /proc/self/environ, or application configuration files
4. Remote code execution — chain the LFI with a writable log file or upload vulnerability to achieve full remote code execution on the target server

Each step depends directly on the information revealed by the .bak file. Without the paths, versions, and configuration state disclosed, the attacker would need to guess or probe blindly — significantly increasing detection risk and reducing success probability.

Industry Impact: How Widespread Is This Vulnerability?

The phpinfo.php.bak exposure remains one of the most persistent and widespread information disclosure issues in web infrastructure security. Industry-wide measurements from 2025 and early 2026 provide the following context:

Why E-Commerce and Financial Sectors Are Disproportionately Affected

E-commerce and financial services organizations carry the highest exposure rates because they rely heavily on PHP-based platforms such as Magento, WooCommerce, and custom payment processing applications. These platforms often undergo frequent development cycles, migration events, and third-party vendor integrations — each creating opportunities for debug files and backups