Executive brief
Gotenberg is a tool used to convert various document formats into PDFs via an API. A security flaw allows unauthenticated users to bypass safety filters designed to prevent the tool from connecting to internal company networks. An attacker could use this to access sensitive internal data, private services, or cloud infrastructure metadata that should not be reachable from the internet.
Technical details
A Server-Side Request Forgery (SSRF) vulnerability exists in Gotenberg's webhook and download-from features due to case-sensitive regular expression matching. The default deny-list uses the regex '^https?://', which fails to match capitalized schemes like 'HTTP://' or 'Https://'. Because the underlying Go net/url.Parse() function normalizes these schemes to lowercase before initiating a connection, an attacker can bypass the security filter to reach internal IP ranges, loopback addresses, and cloud metadata endpoints (e.g., 169.254.169.254). This is a regression or similar flaw to CVE-2026-27018. The issue is fixed in version 8.31.0 by ensuring case-insensitive matching or normalization before filtering.
Affected products
- Gotenberg Gotenberg <= 8.30.1
Timeline
- 2026-04-07: other: Vulnerable code introduced in commit 3f01ca1
- 2026-05-05: disclosed: Initial advisory published
- 2026-05-05: patched: Fixed in version 8.31.0