CVE-2018-8625 : Détail

CVE-2018-8625

7.5
/
Haute
Memory Corruption
83.96%V3
Network
2018-12-11
23h00 +00:00
2018-12-21
09h57 +00:00
CVE.org
NVD
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Descriptions du CVE

A remote code execution vulnerability exists in the way that the VBScript engine handles objects in memory, aka "Windows VBScript Engine Remote Code Execution Vulnerability." This affects Internet Explorer 9, Internet Explorer 11, Internet Explorer 10.

Informations du CVE

Faiblesses connexes

CWE-ID Nom de la faiblesse Source
CWE-416 Use After Free
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.

Métriques

Métriques Score Gravité CVSS Vecteur Source
V3.0 7.5 HIGH CVSS:3.0/AV:N/AC:H/PR:N/UI:R/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.

Network

A vulnerability exploitable with network access means the vulnerable component is bound to the network stack and the attacker's path is through OSI layer 3 (the network layer). Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable one or more network hops away (e.g. across layer 3 boundaries from routers).

Attack Complexity

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

High

A successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected.

Privileges Required

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

None

The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.

User Interaction

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

Required

Successful exploitation of this vulnerability requires a user to take some action before the vulnerability can be exploited. For example, a successful exploit may only be possible during the installation of an application by a system administrator.

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 7.6 AV:N/AC:H/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 : 46022

Date de publication : 2018-12-19 23h00 +00:00
Auteur : Google Security Research
EDB Vérifié : Yes

There is an reference leak in Microsoft VBScript that can be turned into an use-after-free given sufficient time. The vulnerability has been confirmed in Internet Explorer on various Windows versions with the latest patches applied. Details: VbsErase function is used to reset and free the contents of a VBScript array. When this function is called on a VBScript variable of the type array (implemented as a VAR structure containing a type followed by a value, in this case a pointer to a SafeArray object), the function follows these steps: 1. Get the pointer to a SafeArray object from the VBScript variable and store it locally 2. Set the pointer value in the VBScript variable to 0 (null) 3. Release the array members (by calling SafeArrayDestroyData) 4. Restore the pointer from step 2 5. Destroy the array object itself (by calling SafeArrayDestroyDescriptor) 6. Once again, set the pointer value in the VBScript variable to null The dance with setting the pointer to null and restoring it was made to address previously reported vulnerabilities described in http://blogs.360.cn/post/from-a-patched-itw-0day-to-remote-code-execution-part-i-from-patch-to-new-0day.html. However, this also introduced another bug. Specifically, if during SafeArrayDestroyData a user-defined callback runs, the callback can set the value of the VBScript variable passed to VbsErase to some other object (which increases the reference count of the object). If that happens, in steps 4 and 6 above, the pointer to the object will be overwritten, thus preventing its reference count to get properly decremented when the VBScript variable is assigned some other value. Consider the following code snippet: ==================================== Class class1 End Class Class class2 Private Sub Class_Terminate() ' increase the reference count of c set a = c End Sub End Class ' create an object of class1 and increase its reference count c = new class1 a = Array(0) set a(0) = new class2 ' call Class_Terminate of class2 Erase a ' a has been set to null so the following line doesn't affect c in any way a = 1 ' decrease the reference count of c c = 1 ' at this point the referenc couter of c is 1 instead of 0 ==================================== When the code snippet finishes, the class1 object createad on the first line continues to live, even though all references to it have been lost so it should have been destroyed. This same principle can be used to increase the reference count of an arbitrary object any number of times without incurring a memory cost, eventually overflowing the 32-bit reference counter. Note that, while custom classes in VBScript have protection against overflowing a reference counter, this isn't the case for built-in objects (compare VBScriptClass::AddRef to AddRef methods of other classes). Because of this, the PoCs below use a RegExp object. The only problem is that for every reference counter increment, a new array has to be created and destroyed and a user-defined Class_Terminate needs to run which all takes time. Overflowing the 32-bit reference counter can take around 2 hours (depending on the CPU) and way longer if page heap is enabled for the iexplore.exe process. leak1.html (in attachment) contains the full PoC and leak1.txt contains a debug log for this. If you don't want to wait, a quicker way to demonstrate the issue is to just run the reference counter increase for certain number of iterations, and then increase it further (close to overflowing) via a debugger. leak2.html demonstrates this and leak2.txt contains the debug log (obtained in a 64 bit process with page heap enabled). Proof of Concept: https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/46022.zip

Products Mentioned

Configuraton 0

Microsoft>>Internet_explorer >> Version 9

Microsoft>>Windows_server_2008 >> Version -

Configuraton 0

Microsoft>>Internet_explorer >> Version 10

Microsoft>>Windows_server_2012 >> Version -

Configuraton 0

Microsoft>>Internet_explorer >> Version 11

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_7 >> Version -

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_2019 >> Version -

Références

http://www.securityfocus.com/bid/106122
Tags : vdb-entry, x_refsource_BID
https://www.exploit-db.com/exploits/46022/
Tags : exploit, x_refsource_EXPLOIT-DB