CVE-2023-38491 (published 2023-07-27T16:15Z)

Kirby is a content management system. A vulnerability in versions prior to 3.5.8.3, 3.6.6.3, 3.7.5.2, 3.8.4.1, and 3.9.6 affects all Kirby sites that might have potential attackers in the group of authenticated Panel users or that allow external visitors to upload an arbitrary file to the content folder. Kirby sites are not affected if they don't allow file uploads for untrusted users or visitors or if the file extensions of uploaded files are limited to a fixed safe list. The attack requires user interaction by another user or visitor and cannot be automated.\n\nAn editor with write access to the Kirby Panel could upload a file with an unknown file extension like `.xyz` that contains HTML code including harmful content like `<script>` tags. The direct link to that file could be sent to other users or visitors of the site. If the victim opened that link in a browser where they are logged in to Kirby and the file had not been opened by anyone since the upload, Kirby would not be able to send the correct MIME content type, instead falling back to `text/html`. The browser would then run the script, which could for example trigger requests to Kirby's API with the permissions of the victim.\n\nThe issue was caused by the underlying `Kirby\\Http\\Response::file()` method, which didn't have an explicit fallback if the MIME type could not be determined from the file extension. If you use this method in site or plugin code, these uses may be affected by the same vulnerability.\n\nThe problem has been patched in Kirby 3.5.8.3, 3.6.6.3, 3.7.5.2, 3.8.4.1, and 3.9.6. In all of the mentioned releases, the maintainers have fixed the affected method to use a fallback MIME type of `text/plain` and set the `X-Content-Type-Options: nosniff` header if the MIME type of the file is unknown.

CVSS v3 base score: 5.4, MEDIUM (CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N)

Weakness information:
cwe_id: CWE-79
cwe_name: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
description: The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.
extended_description: 
            Cross-site scripting (XSS) vulnerabilities occur when:
            
               Untrusted data enters a web application, typically from a web request.
               The web application dynamically generates a web page that contains this untrusted data.
               During page generation, the application does not prevent the data from containing content that is executable by a web browser, such as JavaScript, HTML tags, HTML attributes, mouse events, Flash, ActiveX, etc.
               A victim visits the generated web page through a web browser, which contains malicious script that was injected using the untrusted data.
               Since the script comes from a web page that was sent by the web server, the victim's web browser executes the malicious script in the context of the web server's domain.
               This effectively violates the intention of the web browser's same-origin policy, which states that scripts in one domain should not be able to access resources or run code in a different domain.
            
            There are three main kinds of XSS:
            
               
                  Type 1: Reflected XSS (or Non-Persistent) - 
         			The server reads data directly from the HTTP request and reflects it back in the HTTP response. Reflected XSS exploits occur when an attacker causes a victim to supply dangerous content to a vulnerable web application, which is then reflected back to the victim and executed by the web browser. The most common mechanism for delivering malicious content is to include it as a parameter in a URL that is posted publicly or e-mailed directly to the victim. URLs constructed in this manner constitute the core of many phishing schemes, whereby an attacker convinces a victim to visit a URL that refers to a vulnerable site. After the site reflects the attacker's content back to the victim, the content is executed by the victim's browser.
               
                  Type 2: Stored XSS (or Persistent) - 
               The application stores dangerous data in a database, message forum, visitor log, or other trusted data store. At a later time, the dangerous data is subsequently read back into the application and included in dynamic content. From an attacker's perspective, the optimal place to inject malicious content is in an area that is displayed to either many users or particularly interesting users. Interesting users typically have elevated privileges in the application or interact with sensitive data that is valuable to the attacker. If one of these users executes malicious content, the attacker may be able to perform privileged operations on behalf of the user or gain access to sensitive data belonging to the user. For example, the attacker might inject XSS into a log message, which might not be handled properly when an administrator views the logs.
            
               
                  Type 0: DOM-Based XSS - 
               In DOM-based XSS, the client performs the injection of XSS into the page; in the other types, the server performs the injection. DOM-based XSS generally involves server-controlled, trusted script that is sent to the client, such as Javascript that performs sanity checks on a form before the user submits it. If the server-supplied script processes user-supplied data and then injects it back into the web page (such as with dynamic HTML), then DOM-based XSS is possible.
            
            
            Once the malicious script is injected, the attacker can perform a variety of malicious activities. The attacker could transfer private information, such as cookies that may include session information, from the victim's machine to the attacker. The attacker could send malicious requests to a web site on behalf of the victim, which could be especially dangerous to the site if the victim has administrator privileges to manage that site. Phishing attacks could be used to emulate trusted web sites and trick the victim into entering a password, allowing the attacker to compromise the victim's account on that web site. Finally, the script could exploit a vulnerability in the web browser itself possibly taking over the victim's machine, sometimes referred to as "drive-by hacking."
            In many cases, the attack can be launched without the victim even being aware of it. Even with careful users, attackers frequently use a variety of methods to encode the malicious portion of the attack, such as URL encoding or Unicode, so the request looks less suspicious.
         
         

Fix information:
repo_url: https://github.com/getkirby/kirby
commit_details: repo_url: https://github.com/getkirby/kirby
author: Lukas Bestle
author_date: 2023-07-23 22:17:50+02:00
msg: Fix MIME detection vulnerability

https://github.com/getkirby/kirby/security/advisories/GHSA-8fv7-wq38-f5c9
repository: repo_url: https://github.com/getkirby/kirby
repo_name: getkirby/kirby
description: Kirby's core application folder
repo_language: PHP
owner: getkirby
file_changes: filename: Response.php
change_type: ModificationType.MODIFY
diff: @@ -176,6 +176,18 @@ class Response
 			'type' => F::extensionToMime(F::extension($file))
 		], $props);
 
+		// if we couldn't serve a correct MIME type, force
+		// the browser to display the file as plain text to
+		// harden against attacks from malicious file uploads
+		if ($props['type'] === null) {
+			if (isset($props['headers']) !== true) {
+				$props['headers'] = [];
+			}
+
+			$props['type'] = 'text/plain';
+			$props['headers']['X-Content-Type-Options'] = 'nosniff';
+		}
+
 		return new static($props);
 	}
 

programming_language: PHP
filename: ResponseTest.php
change_type: ModificationType.MODIFY
diff: @@ -188,13 +188,41 @@ class ResponseTest extends TestCase
 
 	public function testFile()
 	{
-		$file = __DIR__ . '/fixtures/download.txt';
+		$file = __DIR__ . '/fixtures/download.json';
+
+		$response = Response::file($file);
+
+		$this->assertSame('application/json', $response->type());
+		$this->assertSame(200, $response->code());
+		$this->assertSame('{"foo": "bar"}', $response->body());
+
+		$response = Response::file($file, [
+			'code'    => '201',
+			'headers' => [
+				'Pragma' => 'no-cache'
+			]
+		]);
+
+		$this->assertSame('application/json', $response->type());
+		$this->assertSame(201, $response->code());
+		$this->assertSame('{"foo": "bar"}', $response->body());
+		$this->assertSame([
+			'Pragma' => 'no-cache'
+		], $response->headers());
+	}
+
+	public function testFileInvalid()
+	{
+		$file = __DIR__ . '/fixtures/download.xyz';
 
 		$response = Response::file($file);
 
 		$this->assertSame('text/plain', $response->type());
 		$this->assertSame(200, $response->code());
 		$this->assertSame('test', $response->body());
+		$this->assertSame([
+			'X-Content-Type-Options' => 'nosniff',
+		], $response->headers());
 
 		$response = Response::file($file, [
 			'code'    => '201',
@@ -207,7 +235,8 @@ class ResponseTest extends TestCase
 		$this->assertSame(201, $response->code());
 		$this->assertSame('test', $response->body());
 		$this->assertSame([
-			'Pragma' => 'no-cache'
+			'Pragma' => 'no-cache',
+			'X-Content-Type-Options' => 'nosniff',
 		], $response->headers());
 	}
 

programming_language: PHP
filename: download.json
change_type: ModificationType.ADD
diff: @@ -0,0 +1 @@
+{"foo": "bar"}
\ No newline at end of file

programming_language: SQL