Gotenberg has Chromium deny-list bypass via case-insensitive URL scheme (bypass of GHSA-rh2x-ccvw-q7r3)

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

7.8 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N/E:P · score source

EPSS

• CVE-2026-27018: 1.70% estimated exploitation activity in the next 30 days; percentile 77.24 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact The fix introduced in version 8.1.0 for GHSA-rh2x-ccvw-q7r3 (CVE-2024-21527) can be bypassed using mixed-case or uppercase URL schemes. The default --chromium-deny-list value is ^file:(?!//\/tmp/).. This regex is anchored to lowercase file: at the start. However, per RFC 3986 Section 3.1, URI schemes are case-insensitive. Chromium normalizes the scheme to lowercase before navigation, so a URL like FILE:///etc/passwd or File:///etc/passwd bypasses the deny-list check but still gets resolved by Chromium as file:///etc/passwd. The root cause is in pkg/gotenberg/filter.go — the FilterDeadline function compiles the deny-list regex with regexp2.MustCompile(denied.String(), 0), where 0 means no flags (case-sensitive). Since the regex pattern itself doesn't include a (?i) flag, matching is strictly case-sensitive. This affects both the URL endpoint and HTML conversion (via iframes, link tags, etc.). Steps to Reproduce 1. Start Gotenberg with default settings: 2. Read /etc/passwd via…

Published by the source

30 Mar 2026, 16:16 UTC

Last modified by the source

6 Apr 2026, 17:26 UTC

Source last checked

26 Oct 2026, 15:19 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-jjwv-57xh-xr6r

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# Patch Next advisory brief: CVE-2026-27018

Advisory: Gotenberg has Chromium deny-list bypass via case-insensitive URL scheme (bypass of GHSA-rh2x-ccvw-q7r3)
IDs: CVE-2026-27018, GHSA-jjwv-57xh-xr6r
Record: https://patchnext.com/advisories/cve-2026-27018 (revision 1, source checked 26 Oct 2026, 15:19 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Partial vendor fix; fixed versions by package: github.com/gotenberg/gotenberg/v8 8.29.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/gotenberg/gotenberg/v7: affected <= 7.10.2
- Go github.com/gotenberg/gotenberg/v8: affected < 8.29.0; fixed in 8.29.0

## Suggested inspection (read-only)
- Go github.com/gotenberg/gotenberg/v7: check the installed version with your package manager.
- Go github.com/gotenberg/gotenberg/v8: check the installed version with your package manager.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/gotenberg/gotenberg/v7, github.com/gotenberg/gotenberg/v8.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-jjwv-57xh-xr6r (GitHub-reviewed advisory GHSA-jjwv-57xh-xr6r lists affected ranges: Go github.com/gotenberg/gotenberg/v8 >=0 =0 <=7.10.2)

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