Executive brief
Shlink is a URL shortening service that can automatically resolve and display page titles from long URLs. A vulnerability in this feature allows authenticated users with an API key to make the Shlink server perform HTTP requests to internal network resources and leak the titles of those pages back to the attacker. This could expose sensitive internal systems and services that should not be accessible from the internet.
Technical details
The vulnerability is a Server-Side Request Forgery (SSRF) in the automatic title-resolution helper used during short URL creation and editing. When AUTO_RESOLVE_TITLES is enabled and no explicit title is supplied, the application performs a server-side GET request to the user-controlled longUrl parameter without validating that it points to an external, safe destination. The vulnerable component accepts URL-shaped values and does not enforce internal-address blocking before fetching the URL. An authenticated attacker with a valid API key can trigger requests to internal HTTP services; the fetched page title is then stored or returned with the short URL, providing a response-content disclosure primitive. Attack preconditions include the AUTO_RESOLVE_TITLES feature being enabled and the attacker possessing a valid API key. No patch has been released as of the advisory publication date.
Affected products
- shlinkio shlink <= 5.0.1
Timeline
- 2026-06-15: disclosed: Vulnerability published to GitHub Advisory Database and NVD
- 2026-08-27: advisory: GitHub security review completed