GHSA-jjwv-57xh-xr6r CVE-2026-27018 GO-2026-4905
Gotenberg has Chromium deny-list bypass via case-insensitive URL scheme (bypass of GHSA-rh2x-ccvw-q7r3)
High
Go
- Severity
- 0.0 / 10
- High · CVSS 4.0
- Exploit chance (EPSS)
- 1.70%
- Chance of exploitation in the next 30 days. Higher than 77.22% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Weakness
- CWE-22 Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
- CWE-918 Server-Side Request Forgery (SSRF)
- Fix
8.29.0- Upgrade github.com/gotenberg/gotenberg/v8 to this version or later
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
- Start Gotenberg with default settings:
docker run --rm -p 3000:3000 gotenberg/gotenberg:8.26.0 gotenberg
- Read
/etc/passwdvia 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
-
Open
output.pdf— it contains the contents of/etc/passwd. -
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
- The resulting PDF contains
/etc/passwdcontents.
Mixed-case variants like File:, fILE:, fiLE: etc. all work as well.
Root Cause
pkg/modules/chromium/chromium.godefines the default deny-list as^file:(?!//\/tmp/).*pkg/gotenberg/filter.gocompiles this withregexp2.MustCompile(denied.String(), 0)— flag0means case-sensitivepkg/modules/chromium/events.gousesFilterDeadlineto check intercepted request URLs against the deny-list- Chromium normalizes URL schemes to lowercase, so
FILE:///etc/passwdbecomesfile:///etc/passwdafter 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.
Affected versions
Go
| Package | Vulnerable | Fixed in |
|---|---|---|
| github.com/gotenberg/gotenberg/v7 | <= 7.10.2 |
No fix yet |
| github.com/gotenberg/gotenberg/v7 | all versions |
No fix yet |
| github.com/gotenberg/gotenberg/v8 | < 8.29.0 |
8.29.0 |
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
github.com/gotenberg/gotenberg/v8 Go → 8.29.0
- go
go get github.com/gotenberg/gotenberg/v8@v8.29.0 && go mod tidy
Severity breakdown
CVSS 4.0 0.0
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
- Attack vector
- Network
- Attack complexity
- Low
- Attack requirements
- None
- Privileges required
- None
- User interaction
- None
- Confidentiality (vulnerable system)
- High
- Integrity (vulnerable system)
- Low
- Availability (vulnerable system)
- None
- Confidentiality (subsequent systems)
- None
- Integrity (subsequent systems)
- None
- Availability (subsequent systems)
- None
- Exploit maturity
- Proof of concept
CVSS 3.1 7.5
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- None
- Availability
- None
Weakness
CWE-22: 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.
How to prevent it
- Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright. When validating filenames, use stringent allowlists that limit the character set to be used. If feasible, only allow a single "." character in the filename to avoid weaknesses such as CWE-23, and exclude directory separators such as "/" to avoid CWE-36. Use a list of allowable file extensions, which will help to avoid CWE-434. Do not rely exclusively on a filtering mechanism that removes potentially dangerous characters. This is equivalent to a denylist, which may be incomplete (CWE-184). For example, filtering "/" is insufficient protection if the filesystem also supports the use of "\" as a directory separator. Another possible error could occur when the filtering is applied in a way that still produces dangerous data (CWE-182). For example, if "../" sequences are removed from the ".../...//" string in a sequential fashion, two instances of "../" would b
- Architecture and Design: For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
- Implementation: Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked. Use a built-in path canonicalization function (such as realpath() in C) that produces the canonical version of the pathname, which effectively removes ".." sequences and symbolic links (CWE-23, CWE-59). This includes: realpath() in C getCanonicalPath() in Java GetFullPath() in ASP.NET realpath() or abs_path() in Perl realpath() in PHP
- Architecture and Design: Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid [REF-1482].
- Operation: Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth [REF-1481].
- Architecture and Design, Operation: Run your code using the lowest privileges that are required to accomplish the necessary tasks [REF-76]. If possible, create isolated accounts with limited privileges that are only used for a single task. That way, a successful attack will not immediately give the attacker access to the rest of the software or its environment. For example, database applications rarely need to run as the database administrator, especially in day-to-day operations.
- Architecture and Design: When the set of acceptable objects, such as filenames or URLs, is limited or known, create a mapping from a set of fixed input values (such as numeric IDs) to the actual filenames or URLs, and reject all other inputs. For example, ID 1 could map to "inbox.txt" and ID 2 could map to "profile.txt". Features such as the ESAPI AccessReferenceMap [REF-185] provide this capability.
- Architecture and Design, Operation: Run the code in a "jail" or similar sandbox environment that enforces strict boundaries between the process and the operating system. This may effectively restrict which files can be accessed in a particular directory or which commands can be executed by the software. OS-level examples include the Unix chroot jail, AppArmor, and SELinux. In general, managed code may provide some protection. For example, java.io.FilePermission in the Java SecurityManager allows the software to specify restrictions on file operations. This may not be a feasible solution, and it only limits the impact to the operating system; the rest of the application may still be subject to compromise. Be careful to avoid CWE-243 and other weaknesses related to jails.
- Architecture and Design, Operation: Store library, include, and utility files outside of the web document root, if possible. Otherwise, store them in a separate directory and use the web server's access control capabilities to prevent attackers from directly requesting them. One common practice is to define a fixed constant in each calling program, then check for the existence of the constant in the library/include file; if the constant does not exist, then the file was directly requested, and it can exit immediately. This significantly reduces the chance of an attacker being able to bypass any protection mechanisms that are in the base program but not in the include files. It will also reduce the attack surface.
- Implementation: Ensure that error messages only contain minimal details that are useful to the intended audience and no one else. The messages need to strike the balance between being too cryptic (which can confuse users) or being too detailed (which may reveal more than intended). The messages should not reveal the methods that were used to determine the error. Attackers can use detailed information to refine or optimize their original attack, thereby increasing their chances of success. If errors must be captured in some detail, record them in log messages, but consider what could occur if the log messages can be viewed by attackers. Highly sensitive information such as passwords should never be saved to log files. Avoid inconsistent messaging that might accidentally tip off an attacker about internal state, such as whether a user account exists or not. In the context of path traversal, error messages which disclose path information can help attackers craft the appropriate attack strings to move through the file system hierarchy.
- Operation, Implementation: When using PHP, configure the application so that it does not use register_globals. During implementation, develop the application so that it does not rely on this feature, but be wary of implementing a register_globals emulation that is subject to weaknesses such as CWE-95, CWE-621, and similar issues.
CWE-918: 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.
References
Advisories
Packages
Other links
- github.com/gotenberg/gotenberg/security/advisories/GHSA-jjwv-57xh-xr6r
- github.com/gotenberg/gotenberg/security/advisories/GHSA-rh2x-ccvw-q7r3
- github.com/gotenberg/gotenberg/commit/06b2b2e10c52b58135edbfe82e94d599eb0c5a11
- github.com/gotenberg/gotenberg/commit/8625a4e899eb75e6fcf46d28394334c7fd79fff5
- github.com/gotenberg/gotenberg/releases/tag/v8.29.0
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-5q7p-7jgv-ww56 Gotenberg has case-insensitive URL scheme that bypasses webhook and downloadFrom deny-list SSRF protection | High | Linked by the source |
| GHSA-2mrg-35hw-x3x9 Gotenberg: SSRF via LibreOffice document processing | High | Also affects github.com/gotenberg/gotenberg/v7 |
| GHSA-vp73-vjw8-8f32 Gotenberg has a Race Condition via Multipart `downloadFrom` Handling | High | Also affects github.com/gotenberg/gotenberg/v7 |
| GHSA-86m8-88fq-xfxp Gotenberg has an SSRF deny-list bypass in IsPublicIP via IPv6 6to4 / NAT64 / site-local prefixes | High | Also affects github.com/gotenberg/gotenberg/v7 |
| GHSA-hwc4-gmrw-5222 Gotenberg has path traversal in zip entry name via Windows-style separators in upload filename | High | Also affects github.com/gotenberg/gotenberg/v7 |
| GHSA-chwh-f6gm-r836 Gotenberg: Server-Side Request Forgery via Chromium URL Endpoint with Redirect-Based Deny-List Bypass | High | Also affects github.com/gotenberg/gotenberg/v7 |
| GHSA-g924-cjx7-2rjw Gotenberg allows Chromium URL conversion routes to read arbitrary files under /tmp via file:// scheme | Medium | Also affects github.com/gotenberg/gotenberg/v7 |
| GHSA-4vmc-gm8v-m35h Gotenberg vulnerable to unauthenticated SSRF via default deny-list bypass in downloadFrom and webhook | Critical | Also affects github.com/gotenberg/gotenberg/v7 |
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