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HighCISA KEVExploited in the wildPublic exploit

Windows MSHTML Platform Remote Code Execution Vulnerability

IdentifiersCVE-2021-33742CWE-94

CVE-2021-33742 is a remote code execution vulnerability in the Windows MSHTML platform, the Internet Explorer browser engine used by IE and by applications that embed the WebBrowser/MSHTML component. The provided content states that Google TAG reported this Internet Explorer zero-day was used in 2021 via malicious Office documents and that Microsoft patched it in June 2021. Based on the available information, exploitation involved delivering a crafted Office document that triggered the MSHTML/IE engine to process attacker-controlled web content, resulting in code execution on the target system. The content does not provide the specific vulnerable function or root-cause details beyond identifying the affected component as MSHTML.

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ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation can result in remote code execution on the victim system in the security context of the current user. In the reported activity, the vulnerability was used as part of Candiru-linked intrusion chains to compromise selected targets. This would allow an attacker to execute payloads, install spyware such as DevilsTongue, access data available to the user, and establish further footholds on the host. Impact severity depends on the privileges of the user opening the malicious document; users with administrative rights would expose the system to broader compromise.

Mitigation

If you can’t patch tonight, do this now.

Until patching is complete, reduce exposure by blocking or strictly controlling delivery of untrusted Office documents, especially documents received via email or external messaging. Use Protected View, application control, and attack surface reduction rules to limit Office from launching or retrieving active content. Restrict or disable use of the Internet Explorer/MSHTML engine where operationally feasible, and monitor for suspicious Office child processes, abnormal mshtml-related activity, and document-initiated network requests to attacker-controlled infrastructure. Least-privilege user configurations reduce post-exploitation impact.

Remediation

Patch, then assume compromise.

Apply Microsoft's June 2021 security update addressing CVE-2021-33742 on all supported Windows systems. Prioritize patching endpoints that use Microsoft Office and any applications that invoke the MSHTML/Internet Explorer rendering engine. Validate that legacy IE components and embedded browser controls are updated through normal Windows security servicing. Where possible, reduce or eliminate dependence on the MSHTML/IE engine in enterprise workflows.
PUBLIC EXPLOITS

Exploits

No public exploits tracked yet. Mallory keeps watching.

VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType
Microsoft CorporationWindows 10 1507operating_system
Microsoft CorporationWindows 10 1607operating_system
Microsoft CorporationWindows 10 1809operating_system
Microsoft CorporationWindows 10 1909operating_system
Microsoft CorporationWindows 10 2004operating_system
Microsoft CorporationWindows 10 20h2operating_system
Microsoft CorporationWindows 10 21h1operating_system
Microsoft CorporationWindows 7operating_system
Microsoft CorporationWindows 8.1operating_system
Microsoft CorporationWindows Rt 8.1operating_system
Microsoft CorporationWindows Server 2008operating_system
Microsoft CorporationWindows Server 2008 R2operating_system
Microsoft CorporationWindows Server 2008 Sp2operating_system
Microsoft CorporationWindows Server 2012operating_system
Microsoft CorporationWindows Server 2012 R2operating_system
Microsoft CorporationWindows Server 2016operating_system
Microsoft CorporationWindows Server 2019operating_system

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

2 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.

2 SOURCESView more in app
What this page doesn’t show

The version that knows your environment.

This page is what’s public. Mallory adds the parts that aren’t: which of your assets are affected, which adversaries are exploiting it right now, which detections to deploy, and what to do tonight.
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Exposure mapping

Query your assets running an affected version, and investigate the blast radius.

Threat actor evidence2

Every observed campaign linking this CVE to a named adversary.

Associated malware2

Malware families riding this exploit, with evidence and IOCs.

Detection signatures2

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity

Community discussion across Reddit, Mastodon, and other social sources.

EXTERNAL REFERENCES
MITRE CVE
cve.org · CVE-2021-33742
NVD
nvd.nist.gov/vuln/detail/CVE-2021-33742
MITRE CWE · CWE-94
cwe.mitre.org
Patch
portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-33742
US Government Resource
cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-33742