Threats / Microsoft / CVE-2020-17144
CVE-2020-17144
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-09-19
Microsoft Exchange Server vulnerability
Microsoft Exchange Server improperly validates cmdlet arguments, allowing remote code execution through deserialization of untrusted data.
Verdict
Today item — known-exploited.
An unauthenticated attacker can execute arbitrary code on vulnerable Exchange Server instances by exploiting insufficient argument validation in PowerShell cmdlets. This vulnerability has been actively exploited in the wild.
CISA KEV Yes · 2021-11-035EPSS 0.36514 (verify live)6Exploit Weaponized · public PoC7CVSS 8.43CISA SSVC Exploitation: active · Automatable: yes · Impact: total4
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
3 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).
Probability (EPSS)
EPSS 0.36514 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.
Severity / affected
CVSS 8.4 (CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:H/I:H/A:H/E:P/RL:O/RC:C) · Affected: Microsoft, Exchange Server. Confirm exact fixed builds in the vendor advisory.CVSS — CNA-assigned (CVE.org), version 3.1, set at disclosure.
Weakness (CWE)
Mapped to CWE-502 Deserialization of Untrusted Data — weakness family: Injection.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: yes · 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 329 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 containing a serialized object designed to bypass cmdlet argument validation.
Business
The organization's Exchange infrastructure becomes a direct attack surface accessible from the network perimeter.
2
Keys to the kingdom — privilege/identity takeover narrative 2
Attacker
I send the crafted payload to the vulnerable Exchange Server endpoint, triggering unsafe deserialization.
Business
The server processes untrusted data without proper validation, creating an execution pathway.
3
Lateral reach — past segmentation narrative 3
Attacker
I achieve remote code execution with the privileges of the Exchange Server process.
Business
The attacker gains control of a critical messaging system and can access sensitive communications, user data, and internal infrastructure.
4
Data at risk — exfiltration narrative 4
Attacker
I establish persistence and move laterally through the network using compromised Exchange credentials and access.
Business
The breach expands beyond email to compromise domain controllers, file servers, and other enterprise systems.
5
Lights out — disruption & extortion narrative 5
Attacker
I exfiltrate data or deploy additional malware for long-term access.
Business
The organization faces data loss, regulatory penalties, operational disruption, and reputational damage from a preventable vulnerability.
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
Coverage & confidence
— what we know, and what we don’tEstablished (cited)
Coverage gaps — stated, not hidden
Disclosure & credit2
Catalogued by microsoftCNA
Credited with finding itzcgonvh from A-TEAM of Legendsec at Qi'anxin Groupfinder
Found an error? Propose a correction.
A correction is a cited counter-claim — it must cite a source,
gets reviewed by a second human, and is never auto-applied. See the
correction convention and our identity
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