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

High severity GitHub Reviewed Published Mar 28, 2026 in gotenberg/gotenberg • Updated Apr 6, 2026

Package

gomod github.com/gotenberg/gotenberg/v7 (Go)

Affected versions

<= 7.10.2

Patched versions

None
gomod github.com/gotenberg/gotenberg/v8 (Go)
< 8.29.0
8.29.0

Description

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:
docker run --rm -p 3000:3000 gotenberg/gotenberg:8.26.0 gotenberg
  1. Read /etc/passwd via the URL endpoint using an uppercase scheme:
curl -X POST 'http://localhost:3000/forms/chromium/convert/url' \
  --form 'url=FILE:///etc/passwd' -o output.pdf

  1. Open output.pdf — it contains the contents of /etc/passwd.

  2. Alternatively, create an index.html:

<iframe src="FILE:///etc/passwd" width="100%" height="100%"></iframe>

Then convert it:

curl -X POST 'http://localhost:3000/forms/chromium/convert/html' \
  -F 'files=@index.html' -o output.pdf
  1. The resulting PDF contains /etc/passwd contents.

Mixed-case variants like File:, fILE:, fiLE: etc. all work as well.

Root Cause

  • pkg/modules/chromium/chromium.go defines the default deny-list as ^file:(?!//\/tmp/).*
  • pkg/gotenberg/filter.go compiles this with regexp2.MustCompile(denied.String(), 0) — flag 0 means case-sensitive
  • pkg/modules/chromium/events.go uses FilterDeadline to check intercepted request URLs against the deny-list
  • Chromium normalizes URL schemes to lowercase, so FILE:///etc/passwd becomes file:///etc/passwd after the deny-list check has already passed

Suggested Fix

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.

Severity

This is effectively the same impact as CVE-2024-21527 — unauthenticated arbitrary file read from the Gotenberg container. An attacker can leak environment variables, configuration, credentials, and other sensitive data.

References

@gulien gulien published to gotenberg/gotenberg Mar 28, 2026
Published to the GitHub Advisory Database Mar 30, 2026
Reviewed Mar 30, 2026
Published by the National Vulnerability Database Mar 30, 2026
Last updated Apr 6, 2026

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity Low
Attack Requirements None
Privileges Required None
User interaction None
Vulnerable System Impact Metrics
Confidentiality High
Integrity Low
Availability None
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
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

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(10th percentile)

Weaknesses

Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory. Learn more on MITRE.

Server-Side Request Forgery (SSRF)

The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination. Learn more on MITRE.

CVE ID

CVE-2026-27018

GHSA ID

GHSA-jjwv-57xh-xr6r

Source code

Credits

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