I appreciate you writing back. But we'll have to agree to disagree. Your security scenarios are just bizarre. It's a lot easier to hack people then going through all the interations you suggest. For one, I've been a sys admin for 20 years and NEVER created a private folder under a public folder. Not in my Novell days, not in my Windows days. The only time I've seen a private folder created under a public folder is the \Users folder, and in that case, the users only have Read and List access to the parent \Users folder, and then Full Control to their own folders. I mean let's debate why users get Full Control to their own folders in the first place. That's a common scenario (it's on nearly every network) and its almost always too many permissions. Do I want my regular end-users changing their folder's security permissions? No. Should any regular end-user have Full Control to any share? No, for the same reason. These are valid, common, security points that really do beg further discussion. You're just making up crap up that isn't overly realistic in the world, then going further to assume that a bonehead administrator compounds the problem by making further insecure decisions. You are essentially say, "If you misconfigure your system and make further insecure choices, someone can hack you." Duh. There's a reason why your "announcements" aren't making the news media...because it isn't news. With that said, you have something valid to say, but so far it just isn't a "security vulnerability" that people need to be aware of. You're a smart person, concentrate on issues that will really give us bang for the buck discussions and issues. Roger ***************************************************************** *Roger A. Grimes, InfoWorld, Security Columnist *CPA, CISSP, MCSE: Security (2000/2003/MVP), CEH, yada...yada... *email: roger_grimes@xxxxxxxxxxxxx or roger@xxxxxxxxxxxxxx *Author of Professional Windows Desktop and Server Hardening (Wrox) *http://www.amazon.com/gp/product/0764599909 ***************************************************************** -----Original Message----- From: 3APA3A [mailto:3APA3A@xxxxxxxxxxxxxxxx] Sent: Friday, March 09, 2007 7:09 AM To: Roger A. Grimes Cc: bugtraq@xxxxxxxxxxxxxxxxx; full-disclosure@xxxxxxxxxxxxxxxxx Subject: Re[2]: Microsoft Windows Vista/2003/XP/2000 file management security issues Dear Roger A. Grimes, --Friday, March 9, 2007, 7:31:54 AM, you wrote to 3APA3A@xxxxxxxxxxxxxxxx: RAG> If Alice deletes Bob's folder (which she could do in some scenarios RAG> because she has the write/modify permission) and re-creates it, she RAG> becomes the Creator Owner and now Bob no longer has the ability to RAG> set permissions on it. As a folder owner Alice can give any permissions to Bob she wants. RAG> If I take your strange assumptions, Bob could re-discover the newly RAG> created folder that Alice made, just like she did (I mean if you RAG> make up crap scenarios, why can't I), and do the same trick back to her. He can, if he knows he must. RAG> And Windows does have a umask-like function. It's called Creator Owner. RAG> It's a well known SID, and the default permissions for it can be RAG> set so that any granular permission you want can be set to be default. I see nothing similar between Creator Owner and umask. BTW, the same article explains why Creator Owner is not 100% solution and why you should not rely on Creator Owner in case of DFS replication. RAG> Vista does have symbolic links, and Windows has supported Junction RAG> Points (similar to symbolic links) since Windows 2000. The main RAG> difference is that Junction Points could only point to local RAG> resources and symbolic links can do remote resources as well. Junction points are very close to Unix mounts, I see no any likeness to symbolic links. Junctions points (and by default, symbolic links in Vista) can only be created by administrators, it prevents symlink attack. And it's right choice. RAG> You've come up with some strange scenarios below, and in all cases RAG> I could easily defeat the problem you are suggesting by using RAG> basic, recommended, security settings. "You never know what is enough unless you know more than enough." William Blake It's quite hard to defeat the threat without knowing it. I'm disagree with you about "recommended security settings". I never saw "disconnect all users and close access to the share" or "check you are still folder owner before copy the data" in instructions on how to create file/folder with restricted access inside public one. Or "xcopy /O doesn't guarantee file can not be accessed during copy operation" or "Do not rely on Creator Owner in case of replication". RAG> Why do you spend your time coming up with such weird scenarios to RAG> focus on? Roger, have you ever used robocopy or xcopy /O? I'm not security columnist, I am system administrator/engineer. For last 10 years I develop and implement a lot of corporate directory structures, replications, and backup/restore policies for many very different organizations. I explain mistakes I can personally make and sometimes I personally did (mixing secure and insecure data, implementing automatic replication to unprotected folders, implementing data restore policies where user can ask system administrator to restore some directory structure to user accessible folder, etc). May be I'm only dumb person who does mistakes like that, most probably not. I call it "properly placed rakes to step on". RAG> You're obviously a creative guy with some Windows security RAG> smarts. Thanks. RAG> Why not focus on more realistic scenarios with more real-world RAG> use? There's plenty of them for us to focus on and to try and RAG> solve. Roger, of cause next time I should concentrate on a single-packet exploitable overflow in IPv6 stack to interest InfoWorld readers. I will not, because it's nothing interesting for me in searching yet another buffer overflow. Let another creative guys who are professional in vulnerability researching to dig it. They have tools, time and money. For me, most valuable vulnerability is one simple enough to be exploited with notepad, because it can be noted by everyone, but was unnoticed for 10 years. RAG> Roger RAG> ***************************************************************** RAG> *Roger A. Grimes, InfoWorld, Security Columnist *CPA, CISSP, MCSE: RAG> Security (2000/2003/MVP), CEH, yada...yada... 3APA3A. MCSE/MCT since Windows NT 4.0. RAG> *email: roger_grimes@xxxxxxxxxxxxx or roger@xxxxxxxxxxxxxx *Author RAG> of Professional Windows Desktop and Server Hardening (Wrox) RAG> *http://www.amazon.com/gp/product/0764599909 RAG> ***************************************************************** RAG> -----Original Message----- RAG> From: 3APA3A [mailto:3APA3A@xxxxxxxxxxxxxxxx] RAG> Sent: Thursday, March 08, 2007 2:59 PM RAG> To: bugtraq@xxxxxxxxxxxxxxxxx; full-disclosure@xxxxxxxxxxxxxxxxx RAG> Subject: Microsoft Windows Vista/2003/XP/2000 file management RAG> security issues RAG> This is an article I promised to publish after Windows RAG> ReadDirectoryChangesW (CVE-2007-0843) [1] issue. It should RAG> explain why you must never place secure data inside insecure directory. RAG> Title: Microsoft Windows Vista/2003/XP/2000 file management RAG> security issues RAG> Author: 3APA3A, http://securityvulns.com/ RAG> Vendor: Microsoft (and potentially another vendors) RAG> Products: Microsoft Windows Vista/2003/XP/2000, Microsoft resource kit RAG> for Windows 2000 and different utilities. RAG> Access Vector: Local RAG> Type: multiple/complex (weak design, insecure file operations, etc) RAG> Original advisory: http://securityvulns.com/advisories/winfiles.asp RAG> Securityvulns.com news: RAG> http://security.nnov.ru/news/Microsoft/Windows/files.html RAG> 0. Intro RAG> This article contains a set of attack scenarios to demonstrate RAG> security weakness in few very common Windows management practices. RAG> Neither of the problem explained is critical, yet combined together they should force RAG> you to review your security practices. I can't even say RAG> "vulnerabilities" because there is no something you can call RAG> "vulnerability". It's just something you believe is secure and it's not. RAG> 1.1 Problem: inability to create secured file / folder in public one. RAG> Attack: folder hijack attack RAG> First, it's simply impossible with standard Windows interface to RAG> create something secured in insecure folder. RAG> Scenario 1.1: RAG> Bob wishes to create "Bob private data" folder in "Public" RAG> folder to place few private files. "Public" has at least "Write" RAG> permissions for "User" group. Bob: RAG> I Creates "Bob private data" folder RAG> II Sets permission for folder to only allow access to folder RAG> himself RAG> III Copies private files into folder RAG> Alice wants to get access to folder Bob created. She RAG> Ia Immediately after folder is created, deletes "Bob private RAG> data" folder and creates "Bob private data" folder again (or RAG> simply takes ownership under "Bob private data" folder if RAG> permissions allow). It makes Alice folder owner. RAG> IIa Immediately after Bob sets permissions, she grants herself RAG> full control under folder. She can do it as a folder owner. RAG> IIIa Reads Bob's private files, because files permissions are RAG> inherited from folder RAG> Alice can use "Spydir" RAG> (http://securityvulns.com/soft/) tool to RAG> monitor files access and automate this process. As you can see, [1] RAG> elevates this problem significantly. RAG> This is not new attack. Unix has "umask" command to protect RAG> administrators and users. Currently, Windows has nothing similar. RAG> CreateFile() API supports setting file ACL on file creation (just like RAG> open() allows to set mode on POSIX systems). ACL can be securely set RAG> only on newly created files. This raises a problem of secure file RAG> creation. RAG> 1.2 Problem: Inability to lock / securely change permissions of already RAG> created file RAG> Attack: pre-open file/directory attack. RAG> There are few classes of insecure file creation attack (attempt to RAG> open existing file), exploitable under Unix with hardlinks or RAG> symlinks. It's believed Windows is not vulnerable to this attacks RAG> because RAG> I. There is no symlinks under Windows. Symlink attacks are not RAG> possible. RAG> II. Security information in NTFS is not stored as a part of RAG> directory entry, it's a part of file data. Hard link attacks are RAG> not possible. RAG> III. File locks in Windows are mandatory. It means, if one RAG> application locks the file, another application can not open RAG> this file, if user doesn't have backup privileges. It mitigate RAG> different file-based attacks. RAG> There is at least one scenario, attacker can succeed without symbolic RAG> link: to steal data written to file created without check for file RAG> existence regardless of file locks and permissions. RAG> Attack description: if attacker can predict filename to be written, he RAG> can create file, open it and share this file for all types of access. RAG> Because locking and permissions are only checked on file open, RAG> attacker retain access to the file even if it's locked and it's RAG> permissions are changed to deny file access to attacker. RAG> Exploit (or useful tool): RAG> http://securityvulns.com/files/spyfile.c RAG> Opens file, shares it for different types of access and logs changes, RAG> keeping the file open. RAG> Compiled version is available from http://securityvulns.com/soft/ RAG> Scenario 1.2.1: RAG> Bob is now aware about folder hijack attack. He use xcopy /O /U /S to RAG> synchronize his files to newly created folder. xcopy /O copies RAG> security information (ownership and permissions) before writing data RAG> to file. RAG> Alice use "Spydir" to monitor newly created folders and files in RAG> Bob's directory. She use Spyfile to create spoofed files in target RAG> directory and waits for Bob to run xcopy. Now, she has full control RAG> under content of Bob's files despite the fact she has no permissions RAG> to access these files. RAG> In a same way directory content may be monitored by pre-opening RAG> directory. RAG> Scenario 1.2.2: RAG> Enterprise directory structure is replicated every day to another RAG> user-writable location in order to alow users to recover suddenly RAG> deleted or modified files. xcopy or robocopy (from resource kit) is RAG> used for replication. Attacker can hijack content of newly created RAG> files in newly created folders. RAG> Same problem may happen on archive extraction or backup restoration. RAG> Vulnerable applications: RAG> xcopy (from all Windows versions), RAG> robocopy (Windows 2000 Resource Kit), RAG> different archivers RAG> backup restoration utilities RAG> By default, xcopy warns user the file exists, unless /Y or /U key is RAG> specified. But RAG> I. /Y is always specified for replication RAG> II. /Y can be specified via COPYCMD environment variable. COPYCMD RAG> environment variable can be created in autoexec.bat file. RAG> Different situations are possible, where autoexec.bat is writable by RAG> attacker, if: RAG> - Default Windows 2000 permissions are used or applied with domain RAG> policy [2]. RAG> - One can try to re-create autoexec.bat using POSIX subsystem RAG> III. Neither xcopy nor other utilities warn user on existing RAG> directory. Pre-open directory attack will always succeed. RAG> As you can see, [1] again dramatically elevates this problem. RAG> 1.3 Problem: user can completely block access to the files RAG> Attack: open file deletion RAG> (including Windows file replication service DoS) RAG> If files is deleted while it's open, it still present in file system RAG> under it's old name until close. Any operation on this file RAG> (including attributes requests) fails, regardless of application RAG> rights and permissions (including backup ones). RAG> Exploit: use spyfile, delete file while it's spied. Now, without RAG> closing spyfile, attempt any operation on this file (e.g. try to RAG> find it's ownership). RAG> Scenario 1.3.1 RAG> Now Bob found an copy application to securely copy files. It deletes RAG> old file before creating new one. But it fails if Alice tries to spy RAG> on Bob files, because attempt to delete file succeeds, but file RAG> still present and is unmanageable. RAG> Scenario 1.3.2 RAG> Windows file replication service (FRS) is used to replicate data RAG> between 2 public DFS folders to distribute load. Folder has RAG> permissions: RAG> Everyone: Add & read RAG> Creator Owner: Full Control RAG> Thouse, Alice has no permissions to delete files created by Bob. RAG> Replicated folder is available as a share on 2 different servers: RAG> \\SERVER1\Share and \\SERVER2\Share. Bob is connected RAG> to \\SERVER1\Share. RAG> Alice uses "Spydir" to monitor files creation by Bob. Every time Bob RAG> creates new file on \\SERVER1\Share, Alice use spyfile to create RAG> file with same name on \\SERVER2\Share. It effectively leads to FRS RAG> collision. While trying to resolve collision, FRS fails to delete RAG> file created by Alice and Bob file is deleted (original file is RAG> moved to special hidden folder only accessible by administrator). RAG> Workaround: never try to use creator-owner based permissions in RAG> replicated folders. RAG> Again, [1] seriously escalates this problem. RAG> 2. Conclusion: RAG> It's simply impossible to securely create something in public folder. RAG> At least DoS conditions are always possible. RAG> Developers should not consider mandatory file locking as a security RAG> feature. RAG> Developers should care about secure file creation to store sensitive RAG> information. CREATE_NEW should always be used and ACL should be set RAG> with lpSecurityAttributes of CreateFile. No attempt to open existing RAG> file should be made. RAG> Never try to create secure folder in public one. If you are forced, RAG> disconnect all users before this operation. RAG> Never use replication, archive extraction or backup restore to RAG> user-accessible folder. RAG> Bob and Alice should finally marry. RAG> 3. Vendor: RAG> All timelines are same with [1]. RAG> [1]. Microsoft Windows ReadDirectoryChangesW information leak RAG> (CVE-2007-0843) RAG> http://security.nnov.ru/news/Microsoft/Windows/ReadDirector.html RAG> [2]. Windows 2000 system partition weak default permissions RAG> http://securityvulns.ru/news2205.html RAG> -- RAG> http://securityvulns.com/ RAG> /\_/\ RAG> { , . } |\ RAG> +--oQQo->{ ^ }<-----+ \ RAG> | ZARAZA U 3APA3A } You know my name - look up my number (The RAG> Beatles) RAG> +-------------o66o--+ / RAG> |/ -- ~/ZARAZA http://securityvulns.com/ Но ведь кому угодно могут прийти в голову яйца, пятки и епископы. (Лем)
