CVE-2026-40280: Gotenberg SSRF via case-insensitive URL scheme bypass in webhook and downloadFrom deny-lists

Vulnerability summary

CVE-2026-40280 is a high (CVSS 7.8) Server-Side Request Forgery vulnerability in gotenberg. EPSS estimates a 1.95% chance of exploitation in the next 30 days, higher than 80.2% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 05-05-2026
   PublishedVulnerability first disclosed.
2. 06-05-2026
   Last modifiedVulnerability information updated.

Description

Gotenberg is an API-based document conversion tool. In versions 8.30.1 and earlier, the default private-IP deny-lists for the --webhook-deny-list and --api-download-from-deny-list flags use a case-sensitive regular expression (^https?://) to match URL schemes. Because Go's net/url.Parse() normalizes the scheme to lowercase before establishing the outbound TCP connection, an attacker can bypass the deny-list by simply capitalizing part of the URL scheme (e.g., HTTP://, HTTPS://, or Http://). This allows unauthenticated requests to reach internal network services, including private IP ranges, loopback addresses, and cloud instance metadata endpoints such as HTTP://169.254.169.254/latest/meta-data/. This bypasses the same security control that was patched in CVE-2026-27018. This issue has been fixed in version 8.31.0.

• CWE-918Server-Side Request ForgeryThe web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.