CVE-2026-18736: Shlink Server-Side Request Forgery via Short URL Title Auto-Resolution
Shlink contains a server-side request forgery vulnerability that allows authenticated API key holders to cause the server to issue arbitrary HTTP GET requests by supplying a crafted long URL during short URL creation with title auto-resolution enabled. Attackers can submit URLs pointing to public hosts that redirect to internal targets, including loopback addresses, link-local ranges, and cloud metadata endpoints such as 169.254.169.254, to exfiltrate internal service information via the HTML title element returned in the short URL creation response.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Configuration
Disable title auto-resolution in Shlink short URL creation to prevent the server from issuing HTTP GET requests to attacker-supplied long URLs (SSRF leading to internal information exfiltration via the HTML title element).
Shlink title auto-resolution = enabled - Compensating control
Block outbound network access from the Shlink server to internal/loopback/link-local and cloud metadata endpoints (including 169.254.169.254) to reduce the impact of SSRF via crafted long URLs.