YOURLS is a self-hosted, customizable URL shortener written in PHP. Prior to 1.10.5, yourls_get_request() extracted the request path without sanitization, after which yourls_sanitize_url() and yourls_esc_url() preserved dot and slash traversal sequences before an attacker-controlled keyword reached file_exists() and include() under YOURLS_PAGEDIR. An unauthenticated remote attacker could traverse outside the intended pages directory and include a local PHP file that was already present on the server, such as an uploaded or injected file, causing the file to execute in the YOURLS web process. This issue is fixed in version 1.10.5.
Affected: Packagist: yourls/yourls
## Summary
YOURLS versions ≤1.10.4 contain an unauthenticated path traversal vulnerability that allows attackers to include and execute arbitrary PHP files on the server without any credentials.
## Details
The vulnerability exists because YOURLS uses **URL sanitization functions** (`yourls_sanitize_url()`, `yourls_esc_url()`) to filter request paths, but these functions are designed to clean URLs, not filesystem paths. They preserve `/` and `.` characters, allowing `../` sequences to pass through unfiltered.
The unsanitized keyword is then directly concatenated into a filesystem path and passed to `file_exists()` and later `include()` operations, enabling path traversal attacks.
**Data Flow:** ``` HTTP Request URI (with ../) ↓ yourls_get_request() (no sanitization) ↓ yourls_sanitize_url() (preserves / and .) ↓ yourls_esc_url() (permits / and . via regex) ↓ Keyword extraction (preserves ../) ↓ file_exists(YOURLS_PAGEDIR . "/$keyword.php") ← Sink ↓ include(YOURLS_PAGEDIR . "/$keyword.php") ← Code Execution ```
## Proof of Concept (POC)
In the concept validation, we assume that the attacker has uploaded a `test.php` file to the web root directory, but it cannot be accessed directly. (Of course, it could also be any path, such as `/tmp/test.php`)
### Setup Place a test file in web root:
`./test.php`: ```php <?php phpinfo(); ?> ``` <img width="502" height="126" alt="image" src="https://github.com/user-attachments/assets/14f33f90-625b-4c65-8a…