Operating System:

[Win]

Published:

24 September 2019

Protect yourself against future threats.

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===========================================================================
                         AUSCERT Security Bulletin

                              ASB-2019.0272.2
        Microsoft Internet Explorer memory corruption vulnerability
                             24 September 2019

===========================================================================

        AusCERT Security Bulletin Summary
        ---------------------------------

Product:              Internet Explorer 9
                      Internet Explorer 11
Operating System:     Windows
Impact/Access:        Execute Arbitrary Code/Commands -- Remote with User Interaction
Resolution:           Patch/Upgrade
CVE Names:            CVE-2019-1367  
Member content until: Thursday, October 24 2019

Revision History:     September 24 2019: Microsoft advise that the
                                         vulnerability is being exploited
                                         in the wild.
                      September 24 2019: Initial Release

OVERVIEW

        Microsoft has released a security update for Internet Explorer
        versions 9 and 11 to address a memory corruption vulnerability. [1]
        
        It is being exploited in the wild. [1] [2]


IMPACT

        "A remote code execution vulnerability exists in the way that the scripting
        engine handles objects in memory in Internet Explorer. The vulnerability could
        corrupt memory in such a way that an attacker could execute arbitrary code in
        the context of the current user. An attacker who successfully exploited the
        vulnerability could gain the same user rights as the current user. If the
        current user is logged on with administrative user rights, an attacker who
        successfully exploited the vulnerability could take control of an affected
        system. An attacker could then install programs; view, change, or delete data;
        or create new accounts with full user rights.
        
        In a web-based attack scenario, an attacker could host a specially crafted
        website that is designed to exploit the vulnerability through Internet Explorer
        and then convince a user to view the website, for example, by sending an email." [1]


MITIGATION

        Microsoft has published security updates for all platforms. [1]
        
        There are also workarounds available for administrators unable to
        install these updates yet:
        "Restrict access to JScript.dll
        
        For 32-bit systems, enter the following command at an administrative command
        prompt:
        
            takeown /f %windir%\system32\jscript.dll cacls %windir%\system32\jscript.dll
            /E /P everyone:N
        
        For 64-bit systems, enter the following command at an administrative command
        prompt:
        
            takeown /f %windir%\syswow64\jscript.dll cacls %windir%\syswow64\jscript.dll
            /E /P everyone:N takeown /f %windir%\system32\jscript.dll cacls
            %windir%\system32\jscript.dll /E /P everyone:N
        
        Impact of Workaround
        
        Implementing these steps might result in reduced functionality for components or
        features that rely on jscript.dll. To be fully protected, Microsoft recommends
        the update be installed as soon as possible. Please revert the mitigation steps
        before installing the update to return to a full state.
        
        By default, IE11, IE10, and IE9 uses Jscript9.dll which is not impacted by this
        vulnerability. This vulnerability only affects certain websites that utilize
        jscript as the scripting engine.
        
        How to undo the workaround
        
        For 32-bit systems, enter the following command at an administrative command
        prompt:
        
            cacls %windir%\system32\jscript.dll /E /R everyone    
        
        For 64-bit systems, enter the following command at an administrative command
        prompt:
        
            cacls %windir%\system32\jscript.dll /E /R everyone    cacls
            %windir%\syswow64\jscript.dll /E /R everyone" [1]


REFERENCES

        [1] CVE-2019-1367 | Scripting Engine Memory Corruption Vulnerability
            https://portal.msrc.microsoft.com/en-us/security-guidance/advisory/CVE-2019-1367

        [2] Microsoft releases out-of-band security update to fix IE zero-day &
            Defender bug
            https://www.zdnet.com/article/microsoft-releases-out-of-band-security-update-to-fix-ie-zero-day-defender-bug/

AusCERT has made every effort to ensure that the information contained
in this document is accurate.  However, the decision to use the information
described is the responsibility of each user or organisation. The decision to
follow or act on information or advice contained in this security bulletin is
the responsibility of each user or organisation, and should be considered in
accordance with your organisation's site policies and procedures. AusCERT
takes no responsibility for consequences which may arise from following or
acting on information or advice contained in this security bulletin.

===========================================================================
Australian Computer Emergency Response Team
The University of Queensland
Brisbane
Qld 4072

Internet Email: auscert@auscert.org.au
Facsimile:      (07) 3365 7031
Telephone:      (07) 3365 4417 (International: +61 7 3365 4417)
                AusCERT personnel answer during Queensland business hours 
                which are GMT+10:00 (AEST).
                On call after hours for member emergencies only.
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