Threats / Microsoft / CVE-2021-40444
CVE-2021-40444
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-06-22
Microsoft MSHTML vulnerability
Microsoft MSHTML remote code execution vulnerability exploited in active ransomware campaigns. EPSS score 0.94 indicates high likelihood of exploitation.
Verdict
Today item, not a backlog item.
Critical remote code execution in MSHTML rendering engine. Active exploitation in ransomware operations. Path traversal component suggests file access abuse enabling code execution. Immediate patching required.
CISA KEV Yes · 2021-11-033Ransomware use Flagged3EPSS 0.97242 (verify live)4Exploit Weaponized · public PoC5
01
Is it exploitable?
— the evidence, ranked above the scoreExploit available
Fully weaponized — public exploit code is cataloged for this vulnerability.We link the existence of the exploit; we do not host or redistribute payloads.
Reported exploitation
41 independent public reports of in-the-wild exploitation are cataloged.Distinct reporting sources (vendor, incident response, government); open them for the underlying claims.
Exploited in the wild
Listed in the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03), flagged for known ransomware use.
Probability (EPSS)
EPSS 0.97242 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.
Severity / affected
Affected: Microsoft, MSHTML. Confirm exact fixed builds in the vendor advisory.
Weakness (CWE)
Mapped to CWE-22 Path Traversal — weakness family: Path traversal / file.CWE assignment from the public NVD record; the weakness class drives how the flaw is exploited.
02
Who’s exploiting it?
— attribution turns risk into urgencyAttribution not established
No confirmed (advisory-backed) threat-actor attribution is established for this record. Absence of a named actor is not absence of compromise — see Coverage & confidence.
03
Why it matters
— the attack path, told twice: adversary, then board1
Front door — unauthenticated access narrative 1
Attacker
I craft a malicious document or web content that exploits MSHTML rendering to execute arbitrary code on the target system.
Business
Attackers gain initial code execution foothold, enabling lateral movement and ransomware deployment across enterprise infrastructure.
2
Keys to the kingdom — privilege/identity takeover narrative 2
Attacker
I leverage path traversal to access restricted files or resources during the exploitation chain, escalating my capabilities within the compromised system.
Business
Attackers obtain sensitive data and system configuration details needed to propagate ransomware and establish persistence.
3
Lateral reach — past segmentation narrative 3
Attacker
I deploy ransomware payloads across the network using the established code execution and elevated access.
Business
Critical business systems become encrypted and inaccessible, forcing operational shutdown and potential ransom demands.
04
What to do
— defensible action- Remediate per the vendor advisory — confirm the fixed build for your version and verify exposure.1
Say it to the boardA vulnerability with this evidence profile is a defensible budget line, not a backlog ticket — fund the change against the proof above.
05