GHSA-6j4c-mgqr-qv76 CVE-2026-75592
Kirby: Access to image files outside of the site root via path traversal in the media handling
- Severity
- 0.0 / 10
- Medium · CVSS 4.0
- Exploit chance (EPSS)
- 0.68%
- Chance of exploitation in the next 30 days. Higher than 52.26% 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')
- Fix
4.9.5- Upgrade getkirby/cms to this version or later
Description
TL;DR
This vulnerability affects all Kirby sites that are deployed in a way that their index root on the server is next to a second directory that is read-accessible to PHP and shares the same name prefix (such as the site with the index root /var/www/site being next to /var/www/site2).
It was possible to create and access thumbnails from media files within such sibling directories that have a valid thumbnail configuration (JSON job file). This can affect staging sites, site backups or other internal sites.
Introduction
A path traversal (also known as directory traversal) vulnerability occurs when untrusted input is used to build a filesystem path without properly confining the result to an intended base directory. By injecting sequences such as ../, an attacker can escape that directory and reach files elsewhere on the server.
Affected components
Kirby's media handler processes requests for files in the media directory that have not been generated yet. It parses the provided path and finds the correct file or asset to generate a thumbnail of. Each thumbnail needs to have a prepared job file (a metadata file with file extension .json) in order to allow the media handler to generate a thumbnail.
The media handler uses filesystem containment checks in several places that are supposed to prevent breakout of the media and index roots of the site.
Impact
In affected releases, the containment checks were incomplete and did not cover the case of a sibling directory next to the containment directory that starts with the same prefix. E.g. a directory site2 passed the containment check of directory site. This allowed attackers to access media files with prepared job files that are stored within such sibling directories of the site's index root, opening the potential for information leaks from sensitive files stored within them, and deleting the job file in the process.
Patches
The problem has been patched in Kirby 4.9.5 and Kirby 5.5.2. Please update to one of these or a later version to fix the vulnerability.
In all of the mentioned releases, we have hardened the containment helpers Kirby\Filesystem\Dir::realpath() and Kirby\Filesystem\F::realpath() to require either an exact match or a DIRECTORY_SEPARATOR boundary, so that a sibling path sharing the same name prefix can no longer pass the check. This prevents access to files outside the index root of the active site. We have also hardened the Asset class to block paths that contain the ../ sequence.
Credits
Thanks to @0x1saac for responsibly reporting the identified issue.
Affected versions
Packagist
| Package | Vulnerable | Fixed in |
|---|---|---|
| getkirby/cms | < 4.9.5 |
4.9.5 |
| getkirby/cms | >= 5.0.0, < 5.5.2 |
5.5.2 |
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.
getkirby/cms Packagist → 4.9.5
- composer
composer require getkirby/cms:^4.9.5
Severity breakdown
CVSS 4.0 0.0
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:N/SA:N
- Attack vector
- Network
- Attack complexity
- Low
- Attack requirements
- Present
- Privileges required
- None
- User interaction
- None
- Confidentiality (vulnerable system)
- None
- Integrity (vulnerable system)
- None
- Availability (vulnerable system)
- None
- Confidentiality (subsequent systems)
- High
- Integrity (subsequent systems)
- None
- Availability (subsequent systems)
- 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.
References
Advisories
Packages
Other links
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-9vx2-j98c-p72w Kirby: Access to image files and limited access to JSON files outside of the site root via path traversal in the media handling | High | Also affects getkirby/cms |
| GHSA-67mx-6wf2-92xp Kirby: File upload permissions are not checked during processing of chunk data | High | Also affects getkirby/cms |
| GHSA-rf2p-vh74-7vvh Kirby: System path exposure from error messages in the REST API | Medium | Also affects getkirby/cms |
| GHSA-r3w8-2c5r-h9j9 Kirby: `pages.access` permission is not checked in the `site/find` REST API route | High | Also affects getkirby/cms |
| GHSA-89cp-7p28-jffg Kirby: Access to files of top-level drafts is not protected by permissions | Medium | Also affects getkirby/cms |
| GHSA-whxw-24jc-cwmv Kirby: External Initialization of the Panel on reverse proxy setups with the `Forwarded` header | Critical | Also affects getkirby/cms |
| GHSA-wr9h-4r83-f4v6 Kirby: Cross-site scripting (XSS) from incomplete HTML/XML sanitization in `Dom::sanitize()` | High | Also affects getkirby/cms |
| GHSA-4v4h-m2qq-ppgw Kirby: Request header injection in `Http\Remote` | Medium | Also affects getkirby/cms |
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