Faiblesses connexes
CWE-ID |
Nom de la faiblesse |
Source |
CWE-863 |
Incorrect Authorization The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check. This allows attackers to bypass intended access restrictions. |
|
Metrics
Metric |
Score |
Sévérité |
CVSS Vecteur |
Source |
V3.0 |
8.8 |
HIGH |
CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
Base: Exploitabilty MetricsThe Exploitability metrics reflect the characteristics of the thing that is vulnerable, which we refer to formally as the vulnerable component. Attack VectorThis metric reflects the context by which vulnerability exploitation is possible. A vulnerability exploitable with Local access means that the vulnerable component is not bound to the network stack, and the attacker's path is via read/write/execute capabilities. In some cases, the attacker may be logged in locally in order to exploit the vulnerability, otherwise, she may rely on User Interaction to execute a malicious file. Attack ComplexityThis metric describes the conditions beyond the attacker's control that must exist in order to exploit the vulnerability. Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component. Privileges RequiredThis metric describes the level of privileges an attacker must possess before successfully exploiting the vulnerability. The attacker is authorized with (i.e. requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources. User InteractionThis metric captures the requirement for a user, other than the attacker, to participate in the successful compromise of the vulnerable component. The vulnerable system can be exploited without interaction from any user. Base: Scope MetricsAn important property captured by CVSS v3.0 is the ability for a vulnerability in one software component to impact resources beyond its means, or privileges. ScopeFormally, Scope refers to the collection of privileges defined by a computing authority (e.g. an application, an operating system, or a sandbox environment) when granting access to computing resources (e.g. files, CPU, memory, etc). These privileges are assigned based on some method of identification and authorization. In some cases, the authorization may be simple or loosely controlled based upon predefined rules or standards. For example, in the case of Ethernet traffic sent to a network switch, the switch accepts traffic that arrives on its ports and is an authority that controls the traffic flow to other switch ports. An exploited vulnerability can affect resources beyond the authorization privileges intended by the vulnerable component. In this case the vulnerable component and the impacted component are different. Base: Impact MetricsThe Impact metrics refer to the properties of the impacted component. Confidentiality ImpactThis metric measures the impact to the confidentiality of the information resources managed by a software component due to a successfully exploited vulnerability. There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact. For example, an attacker steals the administrator's password, or private encryption keys of a web server. Integrity ImpactThis metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component. Availability ImpactThis metric measures the impact to the availability of the impacted component resulting from a successfully exploited vulnerability. There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable). Temporal MetricsThe Temporal metrics measure the current state of exploit techniques or code availability, the existence of any patches or workarounds, or the confidence that one has in the description of a vulnerability. Environmental Metrics
|
[email protected] |
V2 |
4.6 |
|
AV:L/AC:L/Au:N/C:P/I:P/A:P |
[email protected] |
EPSS
EPSS est un modèle de notation qui prédit la probabilité qu'une vulnérabilité soit exploitée.
EPSS Score
Le modèle EPSS produit un score de probabilité compris entre 0 et 1 (0 et 100 %). Plus la note est élevée, plus la probabilité qu'une vulnérabilité soit exploitée est grande.
EPSS Percentile
Le percentile est utilisé pour classer les CVE en fonction de leur score EPSS. Par exemple, une CVE dans le 95e percentile selon son score EPSS est plus susceptible d'être exploitée que 95 % des autres CVE. Ainsi, le percentile sert à comparer le score EPSS d'une CVE par rapport à d'autres CVE.
Informations sur l'Exploit
Exploit Database EDB-ID : 46162
Date de publication : 2019-01-13 23:00 +00:00
Auteur : Google Security Research
EDB Vérifié : Yes
Windows: COM Desktop Broker Elevation of Privilege
Platform: Windows 10 1809 (almost certainly earlier versions as well).
Class: Elevation of Privilege
Security Boundary (per Windows Security Service Criteria): AppContainer Sandbox
Summary:
The COM Desktop Broker doesn’t correctly check permissions resulting in elevation of privilege and sandbox escape.
Description:
Windows 10 introduced “Brokered Windows Runtime Components for side-loaded applications” which allows a UWP application to interact with privileged components by allowing developers to write a custom broker in .NET. Rather than handling this with the existing Runtime Broker a new “Desktop Broker” was created and plumbed into the COM infrastructure. This required changes in COMBASE to instantiate the broker class and RPCSS to control access to the broker.
The stated purpose is only for use by sideloaded enterprise applications, specifically .NET based ones. Looking at the checks in RPCSS for the activation of the broker we can see the check as follows:
HRESULT IsSideLoadedPackage(LPCWSTR *package_name, bool *is_sideloaded) {
PackageOrigin origin;
*is_sideloaded = false;
HRESULT hr = GetStagedPackageOrigin(package_name, &origin);
if (FAILED(hr))
return hr;
*is_sideloaded = origin != PackageOrigin_Store;
return S_OK;
}
This check is interesting because it considered anything to be sideloaded that hasn’t come from the Store. Looking at the PackageOrigin enumeration this includes Inbox applications such as Cortana and Edge both of which process potentially untrusted content from the network. Of course this isn’t an issue if the broker is secure, but…
For a start, as long as RPCSS thinks the current package is side-loaded this feature doesn’t require any further capability to use, or at least nothing checks for one during the process. Even in the side loading case this isn’t ideal, it means that even though a side loaded application is in the sandbox this would allow the application to escape without giving the installer of the application any notice that it has effectively full trust. Contrast this with Desktop Bridge UWP applications which require the “fullTrust” capability to invoke a Win32 application outside the sandbox. This is even more important for a sandbox escape from an Inbox application as you can’t change the capabilities at all without having privileged access. Now, technically you’re supposed to have the appropriate configuration inside the application’s manifest to use this, but that only applies if you’re activating through standard COM Runtime activation routes, instead you can just create an instance of the broker’s class (which is stored in the registry, but at least seems to always be C8FFC414-946D-4E61-A302-9B9713F84448). This class is running in a DLL surrogate at normal user privileges. Therefore any issue with this interface is a sandbox escape. The call implements a single interface, IWinRTDesktopBroker, which looks like:
class IWinRTDesktopBroker : public IUnknown {
HRESULT GetClassActivatorForApplication(HSTRING dir, IWinRTClassActivator** ppv);
};
This interface has only one method, GetClassActivatorForApplication which takes the path to the brokered components directory. No verification of this directory takes place, it can be anywhere you specify. I’d have assumed it might have at least been limited to a special subdirectory of the package installation, but I’d clearly be wrong. Passing an arbitrary directory to this method, you get back the following interface:
class IWinRTClassActivator : public IUnknown {
HRESULT ActivateInstance(HSTRING activatableClassId, IInspectable** ppv);
HRESULT GetActivationFactory(HSTRING activatableClassId, REFIID riid, IUnknown** ppv);
};
So to escape the sandbox with this you can create directory somewhere, copy in a WinRT component winmd file then activate it. The activation process will run class constructors and give you arbitrary code execution outside the sandbox.
However, even if the directory was checked in some way as long as you can get back the IWinRTClassActivator interface you could still escape the sandbox as the object is actually an instance of the System.Runtime.InteropServices.WindowsRuntime.WinRTClassActivator class which is implemented by the .NET BCL. This means that it exposes a managed DCOM object to a low-privileged caller which is pretty simple to exploit using my old serialization attacks (e.g. MSRC case 37122). The funny thing is MSRC wrote a blog post [1] about not using Managed DCOM across security boundaries almost certainly before this code was implemented but clearly it wasn’t understood.
[1] https://blogs.technet.microsoft.com/srd/2014/10/14/more-details-about-cve-2014-4073-elevation-of-privilege-vulnerability/
There are some caveats, as far as I can tell you can’t create this broker from an LPAC Edge content process, more because the connection to the broker fails rather than any activation permissions check. Therefore to exploit from Edge you’d need to get into the MicrosoftEdge process (or another process outside of LPAC). This is left as an exercise for the reader.
Fixing wise, I’d guess unless you’re actually using this for Inbox applications at a minimum you probably should only Developer and LOB origins. Ideally you’d probably want to require a capability for its use but the horse may have bolted on that one. Anyway you might not consider this an issue as it can’t easily be used from LPAC and side-loading is an issue unto itself.
Proof of Concept:
I’ve provided a PoC as a solution containing the C# PoC and Brokered Component as well as a DLL which can be injected into Edge to demonstrate the issue. The PoC will inject the DLL into a running MicrosoftEdge process and run the attack. Note that the PoC needs to know the relative location of the ntdll!LdrpKnownDllDirectoryHandle symbol for x64 in order to work. It should be set up for the initial release of RS5 (17763.1) but if you need to run it on another machine you’ll need to modify GetHandleAddress in the PoC to check the version string from NTDLL and return the appropriate location (you can get the offset in WinDBG using ‘? ntdll!LdrpKnownDllDirectoryHandle-ntdll). Also before you ask, the injection isn’t a CIG bypass you need to be able to create an image section from an arbitrary file to perform the injection which you can do inside a process running with CIG.
1) Compile the solution in “Release” mode for “Any CPU”. It’ll need to pull NtApiDotNet from NuGet to build.
2) Start a copy of Edge.
3) Execute the PoC from the x64\Release directory.
Expected Result:
Creating the broker fails.
Observed Result:
The broker creation succeeds and notepad executes outside the sandbox.
Proof of Concept:
https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/46162.zip
Products Mentioned
Configuraton 0
Microsoft>>Windows_10 >> Version -
Microsoft>>Windows_10 >> Version 1607
Microsoft>>Windows_10 >> Version 1703
Microsoft>>Windows_10 >> Version 1709
Microsoft>>Windows_10 >> Version 1803
Microsoft>>Windows_10 >> Version 1809
Microsoft>>Windows_8.1 >> Version -
Microsoft>>Windows_rt_8.1 >> Version -
Microsoft>>Windows_server_2012 >> Version r2
Microsoft>>Windows_server_2016 >> Version -
Microsoft>>Windows_server_2016 >> Version 1709
Microsoft>>Windows_server_2016 >> Version 1803
Microsoft>>Windows_server_2019 >> Version -
References