# CVE-2026-40280: Gotenberg SSRF deny-list bypass via case-insensitive URL schemes

Source: https://junglewise.ai/threats/cve-2026-40280-gotenberg-ssrf-deny-list-bypass-via-case-insensitive-url-schemes  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-05. Updated: 2026-07-25  
License: CC BY 4.0 with a link back

CVE-2026-40280 · Severity: high · CVSS 7.5 · Published 2026-05-05

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.

Technologies: [github.com/gotenberg/gotenberg/v7 (Go)](https://junglewise.ai/threats/technologies/github-com-gotenberg-gotenberg-v7), [github.com/gotenberg/gotenberg/v8 (Go)](https://junglewise.ai/threats/technologies/github-com-gotenberg-gotenberg-v8), [Gotenberg](https://junglewise.ai/threats/technologies/gotenberg). Vendors: [Go](https://junglewise.ai/threats/vendors/go), [Gotenberg](https://junglewise.ai/threats/vendors/gotenberg).

## Quick answers

**Is CVE-2026-40280 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-40280 being exploited in the wild.

**How severe is CVE-2026-40280?** High severity, with a CVSS score of 7.5, published 5 May 2026.

**Which products and versions are affected?** github.com/gotenberg/gotenberg/v7 (Go) SEMVER:introduced=0; github.com/gotenberg/gotenberg/v8 (Go) SEMVER:introduced=0,fixed=8.31.0; Gotenberg <= 8.30.1.

**Is there a fix for CVE-2026-40280?** Yes. github.com/gotenberg/gotenberg/v8 (Go): upgrade to 8.31.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-40280 attacked?** It is attacked over the network, in a network appliance.

**Am I affected by CVE-2026-40280?** Check whether you run github.com/gotenberg/gotenberg/v7 (Go), github.com/gotenberg/gotenberg/v8 (Go) or Gotenberg at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- github.com/gotenberg/gotenberg/v8 (Go): upgrade to 8.31.0 or later

  ```sh
  go get github.com/gotenberg/gotenberg/v8@v8.31.0
  ```


## 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

## Identifiers

- CVE-2026-40280
- GHSA-5q7p-7jgv-ww56
- GO-2026-5151

## 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

## References

- [https://github.com/gotenberg/gotenberg/commit/3f01ca18d3cc21375a1e2da4b5a3f261c8548e47](https://github.com/gotenberg/gotenberg/commit/3f01ca18d3cc21375a1e2da4b5a3f261c8548e47)
- [https://github.com/gotenberg/gotenberg/security/advisories/GHSA-5q7p-7jgv-ww56](https://github.com/gotenberg/gotenberg/security/advisories/GHSA-5q7p-7jgv-ww56)

## Related threats

- [Gotenberg server-side request forgery in IsPublicIP IPv6 handling](https://junglewise.ai/threats/cve-2026-126799-gotenberg-8-31-0-before-8-38-0-contains-a-server-side-request)
- [Gotenberg race condition in multipart downloadFrom handling](https://junglewise.ai/threats/cve-2026-45742-gotenberg-race-condition-in-multipart-downloadfrom-handling)
- [Gotenberg SSRF deny-list bypass in IsPublicIP via IPv6 prefixes](https://junglewise.ai/threats/cve-2026-45741-gotenberg-ssrf-deny-list-bypass-in-ispublicip-via-ipv6-prefixes)
- [Gotenberg path traversal via Windows-style separators in ZIP entry names](https://junglewise.ai/threats/cve-2026-44829-gotenberg-path-traversal-via-windows-style-separators-in-zip)
- [Gotenberg SSRF and local file disclosure in LibreOffice conversion](https://junglewise.ai/threats/cve-2026-55229-gotenberg-ssrf-and-local-file-disclosure-in-libreoffice)