CVE-2021-34523 · ProxyShell
No source can show you its own past. This one can.
Print this page to keep the view as it stands on this date. Everything hidden behind a disclosure opens, and every receipt prints with its value.
Microsoft Exchange Server Elevation of Privilege Vulnerability
rank 70 = 40 + 19 + 0 + 5 + 6
rank@v1 · act now
Someone is already using it
CISA KEV catalog · public proof-of-concept · FIRST EPSS
EPSS 0.99990 · CISA KEV listed · without this subject the record ranks 30
What it costs you if it fires
NVD CVSS base score, then the CNA's own
CVSS 7.5, from NVD · without this subject the record ranks 51
It is getting worse, not staying still
FIRST EPSS series, rescorings and bad loads removed
no persisting rise in 365 days · without this subject the record ranks 70
How much of the world it touches
NVD CPE configurations
3 products in the CPE ranges · without this subject the record ranks 65
Someone else already set the date
CISA KEV remediation due date
CISA remediation date held · without this subject the record ranks 64
$4.40M = $4.99M incident cost x 0.8814887365328109 exposure x 0.9999 likelihood
udv@v1 · unaudited · wrong for you until you say what you run
$4.99M is the cost of a breach that happened, from IBM Cost of a Data Breach Report 2026, global average. It is not the value of any asset of yours. That average already covers breaches of every severity, so scaling it by exposure understates a partial-impact record. That is an assumption, not a measurement. Your own asset value goes in the decision record.
Hindsight · the state
Foresight · where to check next
No weakness class or product neighbourhood is held for this record, so this index cannot name anywhere to check next. That is an absence in the record, not a finding about the software.
Sources disagree here.
Both shown, dated. We don't pick winners. disagreement-rules@v1
Running Microsoft Exchange Server 2013 Cumulative…? Check your version
A deterministic range check against the ranges this record publishes. It tells you where a version sits in the record, not whether your deployment is exploitable. No account needed.
Watch this record
Matches your own product list against every record this index holds, and tells you when one of them moves.
Set up a watchlist (needs a Practitioner account)
Record your call
Keep your verdict, your reason and the evidence together. The record takes its date when you save it.
AcceptDeferPatch by…Not affectedMitigatedChoose your verdict, then sign in or use an email link. Your first 100 records are free. Evidence is frozen when the record is created.
Private to your organization unless you share it. Put the proof link in your ticket so a reviewer can inspect the basis for your call. See how decision records work.
Harm, if it fires from the vector and the weakness
Written for the ticket you're about to file.
CISA KEV & Federal Remediation Deadline from the record and CISA
The fix, and how long it's been waiting.
Exploit Status & Known PoCs a ladder, not a score
Current rung: Ransomware campaign use known, 2021-11-03.
Affected & Fixed Versions as published
A rung lights from a row in the index, never from an assessment. "Held sources" is the true scope of the claim: this index reads the CVE record, NVD, CISA KEV, FIRST's EPSS and public proof-of-concept repositories, and it does not observe attacks.
What it is stated by the CNA
ProxyShell is the common name for CVE-2021-34523. Microsoft Exchange Server Elevation of Privilege Vulnerability cve-aliases@2026-08-27
NVD's analysis a second authority
- severity
- 7.5 AV:N/AC:L/Au:N/C:P/I:P/A:P
- affected versions
- microsoft exchange server 2013; microsoft exchange server 2016; microsoft exchange server 2019
- also scored by
- [email protected] 9 CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N · [email protected] 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
The CNA scored it 9 and NVD 7.5. Both are shown because both were published; we do not pick one.
check it yourself msrc.microsoft.com receipt
Dated events
Movement the material steps
This score more than doubled inside 72 hours. Both observations are in the full history below.
Show all 116 observations
116 observations held. A highlighted step crossed a promotion threshold. A step marked with a scoring model moved because the instrument was replaced, not because the vulnerability changed. receipt
The full biography
Listed by CISA 112 days after it published, exploit probability more than doubled between 2021-07-20 and 2021-07-23 (0.00624 → 0.06701) and the record had been public for 5 years, 1 month when this index was last written.
No material movement in 24 days as of the last ingest this index recorded.
Siblings and hubs
Records related to this one
Its defect family
microsoft exchange server
Of the 12 records in this family, this is the only one with public proof-of-concept code, and it holds 2 references to it.
Grouped by shared product and weakness, not by shared vulnerability. Each record's own state is on its own page.
Family membership: computed, pro@dim2000
This record is one of a group, and the group's page describes all of them. This page is kept and dated, and the defect family's own page is the one we offer for indexing: the whole group.
Browse the index from here
These are index-wide views, not findings about CVE-2021-34523.
What usually comes next
Everything above needs no account. What is below is work: assembling it, scoping it to your estate, watching it, and handing it to someone else.