Threats / Microsoft / CVE-2021-42278
CVE-2021-42278
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-08-04
Microsoft Active Directory vulnerability
Microsoft Active Directory Domain Services contains an input validation vulnerability enabling privilege escalation. Actively exploited in ransomware campaigns.
Verdict
Today item, not a backlog item.
An unauthenticated or low-privileged attacker can exploit improper input validation in Active Directory to escalate privileges to domain administrator level, facilitating lateral movement and full domain compromise.
CISA KEV Yes · 2022-04-115Ransomware use Flagged5EPSS 0.70207 (verify live)6Exploit Public PoC7CVSS 7.53CISA SSVC Exploitation: active · Automatable: no · Impact: total4
01
Is it exploitable?
— the evidence, ranked above the scoreExploit available
Public proof-of-concept exploit code is cataloged for this vulnerability.We link the existence of the exploit; we do not host or redistribute payloads.
Reported exploitation
15 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 2022-04-11), flagged for known ransomware use.
Probability (EPSS)
EPSS 0.70207 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.
Severity / affected
CVSS 7.5 (CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C) · Affected: Microsoft, Active Directory. Confirm exact fixed builds in the vendor advisory.CVSS — CNA-assigned (CVE.org), version 3.1, set at disclosure.
Weakness (CWE)
Mapped to CWE-20 Improper Input Validation.CWE assignment from the public NVD record (may be stale); the weakness class drives how the flaw is exploited.
CISA SSVC (triage disposition)
Exploitation: active · Automatable: no · Technical Impact: totalCISA's own stakeholder-specific triage inputs, published in the CVE record (CISA Coordinator role). NOTE: this is CISA's three decision points; the final Act/Attend/Track decision also requires a Mission & Well-being input not published here, so no overall decision is asserted.
Currency of the record
CISA added this to its KEV catalog 152 days after the CVE record was published.KEV lag = CISA-KEV dateAdded − CVE.org datePublished; a floor on how long the known-exploited flaw sat in the public record before the federal catalog listed it. Severity/weakness here is CNA- or CISA-assigned (current at disclosure), independent of NVD's analysis backlog.
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 request with specially formatted input to bypass Active Directory validation controls.
Business
Attacker gains unauthorized elevated privileges within the directory service.
2
Keys to the kingdom — privilege/identity takeover narrative 2
Attacker
I leverage elevated privileges to modify directory objects and grant myself domain administrator rights.
Business
Attacker achieves persistent administrative access across the entire Active Directory domain.
3
Lateral reach — past segmentation narrative 3
Attacker
I move laterally across domain-joined systems using administrator credentials.
Business
Attacker establishes presence on critical infrastructure and user endpoints.
4
Data at risk — exfiltration narrative 4
Attacker
I deploy ransomware payloads across the compromised domain.
Business
Organization experiences widespread encryption of business-critical data and operational shutdown.
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