Vulnerability · Published May 5, 2026 · Assigned by GitHub_M
CVE-2026-40280Gotenberg SSRF via case-insensitive URL scheme bypass in webhook and downloadFrom deny-lists
High 7.8
In plain English
A high-severity server-side request forgery in gotenberg from gotenberg. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 1.9% (higher than 80% of all known vulnerabilities). Ready-made attack tooling exists: Nuclei. Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Go | github.com/gotenberg/gotenberg/v7 | no fix listed | GO-2026-5151 |
| Go | github.com/gotenberg/gotenberg/v8 | 8.31.0 | GHSA-5q7p-7jgv-ww56 |
| Go | github.com/gotenberg/gotenberg/v8 | 8.31.0 | GO-2026-5151 |
Affected products (as reported)
Weakness: CWE-918 · Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:L/SA:N
References
- https://github.com/gotenberg/gotenberg/security/advisories/GHSA-5q7p-7jgv-ww56 x_refsource_CONFIRM
- https://github.com/gotenberg/gotenberg/commit/3f01ca18d3cc21375a1e2da4b5a3f261c8548e47 x_refsource_MISC
- https://github.com/advisories/GHSA-jjwv-57xh-xr6r x_refsource_MISC