CVE-2019-1089 : Détail

CVE-2019-1089

7.8
/
Haute
0.05%V3
Local
2019-07-15
16h56 +00:00
2019-07-18
18h06 +00:00
CVE.org
NVD
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Descriptions du CVE

An elevation of privilege vulnerability exists in rpcss.dll when the RPC service Activation Kernel improperly handles an RPC request. To exploit this vulnerability, a low level authenticated attacker could run a specially crafted application. The security update addresses this vulnerability by correcting how rpcss.dll handles these requests., aka 'Windows RPCSS Elevation of Privilege Vulnerability'.

Informations du CVE

Faiblesses connexes

CWE-ID Nom de la faiblesse Source
CWE Other No informations.

Métriques

Métriques Score Gravité CVSS Vecteur Source
V3.0 7.8 HIGH CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Base: Exploitabilty Metrics

The Exploitability metrics reflect the characteristics of the thing that is vulnerable, which we refer to formally as the vulnerable component.

Attack Vector

This metric reflects the context by which vulnerability exploitation is possible.

Local

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 Complexity

This metric describes the conditions beyond the attacker's control that must exist in order to exploit the vulnerability.

Low

Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.

Privileges Required

This metric describes the level of privileges an attacker must possess before successfully exploiting the vulnerability.

Low

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 Interaction

This metric captures the requirement for a user, other than the attacker, to participate in the successful compromise of the vulnerable component.

None

The vulnerable system can be exploited without interaction from any user.

Base: Scope Metrics

An 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.

Scope

Formally, 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.

Unchanged

An exploited vulnerability can only affect resources managed by the same authority. In this case the vulnerable component and the impacted component are the same.

Base: Impact Metrics

The Impact metrics refer to the properties of the impacted component.

Confidentiality Impact

This metric measures the impact to the confidentiality of the information resources managed by a software component due to a successfully exploited vulnerability.

High

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 Impact

This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information.

High

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 Impact

This metric measures the impact to the availability of the impacted component resulting from a successfully exploited vulnerability.

High

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 Metrics

The 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 7.2 AV:L/AC:L/Au:N/C:C/I:C/A:C [email protected]

EPSS

EPSS est un modèle de notation qui prédit la probabilité qu'une vulnérabilité soit exploitée.

Score EPSS

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.

Percentile EPSS

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.
EPSS First.org

Informations sur l'Exploit

Exploit Database EDB-ID : 47135

Date de publication : 2019-07-17 22h00 +00:00
Auteur : Google Security Research
EDB Vérifié : Yes

Windows: RPCSS Activation Kernel Security Callback EoP Platform: Windows 10 1903/1809 (not tested earlier) Class: Elevation of Privilege Security Boundary (per Windows Security Service Criteria): User boundary Summary: The RPCSS Activation Kernel RPC server’s security callback can be bypassed resulting in EoP. Description: The RPCSS service is split into two components, RPCSS which runs as a low-privileged service account and the DCOM launch service which runs as SYSTEM and is responsible for creating new COM processes. Communication between the two services is over an RPC service named Activation Kernel (actkernel). When RPCSS receives a DCOM activation request it will pass that request on to the actkernel service to create new processes. The actkernel RPC service implements various privileged operations, therefore it shouldn’t be callable from a normal user account. However the service must know who made the activation request to RPCSS. This is acheived by RPCSS impersonating the activator while making the RPC request to actkernel which means the ALPC port used by actkernel must be accessible by any process capable of activating a DCOM object, including AC and LPAC. To limit the call to only RPCSS the service implements a security callback on the RPC server which checks the caller process ID the RPCSS service, this should block arbitrary users on the system calling the service. Unfortunately there’s a flaw in this design, RPC defaults to caching the results on these security checks and actkernel doesn’t disable this feature. What this means is once a call is made to actkernel from RPCSS with a user’s token the security result is cached. Now that same user can access actkernel directly as the security callback will not be made and the PID will not be checked. The caching is done primarily on the token’s modified ID, which doesn’t change as often as you’d expect including across ALPC impersonation. As long as the user has made some activation request (such as creating an OOP COM server) then the result is cached and the process can access privileged operations. Looking at what the service exposes an AC sandbox escape might be the best approach. For example the service exposes PrivGetPsmToken which will set an arbitrary SYSAPPID value to a token and return it to the caller. If done from an AC this token is still an AC token in the original package, but with an arbitrary SYSAPPID set which means that security checks which rely on that value can be bypassed. As the AC sid isn’t changed this means it can be impersonated by the caller. This could allow sandbox escape via Browser Broker or Desktop Broker by pretending to be Edge or a side-loaded application. Fixing wise if performance is acceptable then setting the RPC_IF_SEC_NO_CACHE flag on the interface registration should ensure the security callback is always made. You’d probably want to do a search for similar interfaces on Windows. Actkernel might be special in doing a PID check and allowing arbitrary callers via another route but I can’t be sure it’s the only one. Proof of Concept: I’ve provided a PoC as a C# project. It will use the vulnerability to get a token with an arbitrary SYSAPPID. It first respawns the PoC as the calculator AC, then gets a token for MicrosoftEdge. It doesn’t attempt to escape the sandbox, but I’m confident it’d be possible to achieve. 1) Compile the C# project. It’ll need to pull NtApiDotNet from NuGet to build. 2) As a normal user run the PoC. 3) The PoC should print the subkeys of the SAM hive. Expected Result: Accessing the actkernel RPC service should fail with an RPC fault. Observed Result: The actkernel RPC service grants access Proof of Concept: https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/47135.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_10 >> Version 1903

Microsoft>>Windows_7 >> Version -

Microsoft>>Windows_8.1 >> Version -

Microsoft>>Windows_rt_8.1 >> Version -

Microsoft>>Windows_server_2008 >> Version -

Microsoft>>Windows_server_2008 >> Version r2

Microsoft>>Windows_server_2008 >> Version r2

Microsoft>>Windows_server_2012 >> Version -

Microsoft>>Windows_server_2012 >> Version r2

Microsoft>>Windows_server_2016 >> Version -

Microsoft>>Windows_server_2016 >> Version 1803

Microsoft>>Windows_server_2016 >> Version 1903

Microsoft>>Windows_server_2019 >> Version -

Références