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Windows Vista

Windows Vista. Security model and vulnerabilities. Features of Vista Security Model. User account protection (UAP) New in Vista Goal: implement least-privilege user accounts

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Windows Vista

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  1. Windows Vista Security model and vulnerabilities

  2. Features of Vista Security Model • User account protection (UAP) • New in Vista • Goal: implement least-privilege user accounts • Accounts created during installation are protected administrators and subject to UAP, and are limited user accounts (LUA) • When executing without restrictions, a protected administrator user can make changes to key registry, start services, and perform all privileged functions • However, processes launched by that user (including programs) do not inherit this full range of privileges

  3. LUA (continued) • Some processes cannot run properly without administrator privileges • These processes can be allowed to inherit the full privileges from the administrator at launch • A pop-up box will require the user to approve privilege escalation • Claim: no process escalate its privileges without explicit consent from the protected administrator

  4. Integrity levels (privilege levels)

  5. Unprivileged user accounts • Windows Vista (as XP) allows for the creation of standard user accounts (without administrator privileges) • Creation of such accounts require additional steps • Reasonable to expect that non-administrative accounts will be the default in well-managed corporate networks • Reasonable to expect that administrative user accounts will be used by home users for all activities, including browsing the web

  6. Mandatory Integrity Control (MIC) • Also referred as Integrity Levels • New in Vista • Controlled by Access Control Entries (ACE) in System Access Control List (SACL) • Applies to all securable objects (files, processes, registry keys, etc.) • Spawned process inherit parent’s privileges • MIC is enabled/disabled through a windows registry entry

  7. SACL ACE types

  8. Integrity enforcement • A process cannot interact with another process at a higher integrity level directly • However, it is possible for a higher integrity process to directly interact with a lower privilege process • It is possible for a process with any privilege to interact through IPC (named pipes,etc.) • A lower integrity server to impersonate a higher integrity client using calls such as ImpersonateNamedPipeClient, as long as the impersonation level of the client allows it?! • Registry entry keys have associated privilege levels. • For instance, if IE has been given low privileges, it will only have access to a limited section of the registry even if launched by a protected administrator

  9. Other restrictions • A process is not generally able to send windowing messages to higher-privilege processes sharing the desktop • Need to have explicit UI privileges in SACL • Mechanisms to create processes that inherit only some of the user’s privileges via CreateRestrictedToken API. E.g: • Removed privileges • Match only DENY rules for an SID type

  10. Elevation of process privileges • Installer applications • Has extension .msi, matches common installers, or has name SETUP.EXE • Application has a compatibility entry in the registry key or a entry in the compatibility database • Manifest file contains requestedExecutionLevel or requireAdministrator entries • User manually selects “Run Elevated…” by right-clicking the application in Windows Explorer • Lauched through a privileged process without using the restricted API • Fixed bug: Launched through TaskManager • COM objects configured as such in the registry (either builti-in or through user consent)

  11. Lauching from Windows Explorer • Windows explorer has a restricted token and medium integrity level • To launch processes at higher integrity levels, it requests it to AppInfo Admin Broker • RunAsAdminProcesssystem call • Requets user consent (pop-up box) • Triggers CreateProcessAsUser

  12. Registry virtualization • Application developers have traditionally assumed administrator privileges • User-area registry files are written transparently if application requests to write to registry and fails, lacking privilege • User-area registry overrides system registry for that user • Augmented by file virtualization: • C:\Progra~1 (C:\Program Files) to: %UserProfile%\AppData\Local\VirtualStore\C\P rogra~1 • In this fashion, unprivileged applications can modify a localized win.ini, for instance • Special virtualization rules apply to low-integrity processes such as IE

  13. IE7 in Protected Mode Integrity Mechanism IEInstal.exe Admin Broker (High IL) Administrative Rights Required IE7 in protected mode (Low IL) IEUser.exe User Broker (Medium IL) User Rights Required CompatibilityLayer Low Rights Required

  14. Registry protection • Not only files protected, but registry entries • Modifications of system files made only through trusted installer • Trusted installer called for updates (only accepts signed updates) • Resolves a major security issue with earlier windows versions

  15. Privilege escalation • Processes by the same user can be running with medium or high privileges • Since a medium privilege process can write to the current user registry, it can modify entries that control the behavior of the same user’s high-privilege processes (if written to that user’s registry) • By default, user processes and files have medium integrity level, while IE7 (as before) is low integrity • Examples of privilege escalation from low  medium  high  local system are provided by Matthew Conover, Principal Security Researcher, Symantec Corporation, in “Analysis of the Windows Vista Security Model,” a SYMANTEC ADVANCED THREAT RESEARCH technical report

  16. Low to Medium • IE7 cannot write files in the user account or the medium integrity area of the user registry, including adding startup items • But it may be able to connect through the loopback interface to a file sharing service and achieve the same result

  17. Medium to High • Program runs in the background, listening to calls to consent.exe • When it is called, it checks if it has write privileges to the caller • Overwrite the caller with its own malicious code • Launched w/ high privileges

  18. High to LocalSystem • If the high integrity process launched is not LUA restricted, it can • Take ownership of security objects • Change all registry files to grant administrators full privilege to system modification • Apply patches to libraries that disabled signature checking for system files • Modify the operating system arbitrarily • There is no longer monitoring of modification of system files • Still, overall a much stronger security architecture than earlier versions of windows

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