Summary
Gotenberg has Chromium deny-list bypass via case-insensitive URL scheme (bypass of GHSA-rh2x-ccvw-q7r3)
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.).
Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Remediation advice
Change the default deny-list regex to use a case-insensitive flag:
(?i)^file:(?!//\/tmp/).*
Or apply case-insensitive matching in FilterDeadline when compiling the regex.
Frequently Asked Questions
- What is CVE-2026-27018? CVE-2026-27018 is a high-severity path traversal vulnerability in github.com/gotenberg/gotenberg/v8 (go), affecting versions < 8.29.0. It is fixed in 8.29.0. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
- Which packages are affected by CVE-2026-27018?
github.com/gotenberg/gotenberg/v8(go) (versions < 8.29.0)github.com/gotenberg/gotenberg/v7(go) (versions <= 7.10.2)
- Is there a fix for CVE-2026-27018? Yes. CVE-2026-27018 is fixed in 8.29.0. Upgrade to this version or later.
- Is CVE-2026-27018 exploitable, and should I be worried? Whether CVE-2026-27018 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-27018 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-27018? Upgrade
github.com/gotenberg/gotenberg/v8to 8.29.0 or later.