CVE-2021-26419

Scripting Engine Memory Corruption Vulnerability

Recent assessments:

architect00 at May 14, 2021 10:33am UTC reported:

Details

The vulnerability affects Internet Explorer 11 on all Windows Versions. It is located in the jscript9.dll library, which is used to execute javascript.

Possible attack vectors:

• website content

• activeX components in office documents

Google Project Zero released a PoC on 13.05.2021, which triggers the vulnerability and causes a crash. At the time of writing I could not find any weaponized exploit.

The CVSS rating of the vulnerability differs between Windows desktop versions and server versions. In server versions the CVSS Privileges Required is set to High. Desktop versions are rated with CVSS None. The reason could be, that IE enhanced protection mode is disabled on Windows desktop versions and enabled on server versions by default.

Rating explanation

My rating of the exploitability score was affected by the availability of the PoC and the Microsoft exploitability rating. In year 2020, Operation PowerFall was using a similar vulnerability (CVE-2020-1380) in IE. I expect to see exploits for CVE-2021-26419 in a similar context.

Attackers might gain direct control over the host after exploitation without a sandbox escape. IE 11 does have a enhanced protected mode (EPM), which runs IE in an AppContainer and acts as a sandbox. EPM was introduced with Windows 8 and is disabled by default on Windows desktop versions.

Sources

• <https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-26419&gt;

• <https://threatpost.com/wormable-windows-bug-dos-rce/166057/&gt;

• <https://bugs.chromium.org/p/project-zero/issues/detail?id=2157&gt;

• <https://securelist.com/ie-and-windows-zero-day-operation-powerfall/97976/&gt;

• <https://securityintelligence.com/internet-explorer-ie-10-enhanced-protected-mode-epm-sandbox-research/&gt;

• <https://docs.microsoft.com/en-us/troubleshoot/browsers/enhanced-protected-mode-add-on-compatibility&gt;

Assessed Attacker Value: 3
Assessed Attacker Value: 3Assessed Attacker Value: 3