BlackTreeCVE Intelligence
← Back to the CVE catalogue
Full vulnerability report · 2021
CVE-2021-34473High confidence

Microsoft Exchange Server Remote Code Execution Vulnerability

Microsoft · Exchange Server

9.1CriticalCVSS 3.1
Recommended action
Patch now

CISA confirms exploitation in the wild and lists 2021-11-17 as the remediation due date.

Patch available
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityCriticalOperational priority:Critical, unchanged from published severity.unchanged

Evidence used

  • CISA confirms exploitation in the wild.
  • A structured source references public exploit or proof-of-concept material.
  • The selected CVSS metric records a network-reachable, unauthenticated path with no user interaction.
  • EPSS is 100.00% for the current model date.

Compensating controls

  • Validate the affected product branch and deploy the verified fixed release.
  • Restrict the affected network interface to trusted sources where business-safe.
  • Increase monitoring for the attack path and post-exploitation behaviour described in the report.

Verification

  1. Confirm that the asset runs Microsoft Exchange Server and falls inside the recorded affected range.
  2. Verify the installed build against the product-specific fixed version after deployment.
  3. Validate exposure, authentication requirements and compensating controls in the actual environment.
  4. Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Mitigation target: Within 3 daysRemediation target: Within 90 days

This automated reassessment organises public evidence. It does not know asset exposure, business impact or control effectiveness and does not replace CVSS or a human risk decision.

Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Choose official national sources for this report. Each advisory shows its original language. Your selection is remembered on this device and included in shared links.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2021-21128

CISA KEV mirrored by ENISA

Microsoft Exchange Server Remote Code Execution Vulnerability

EUVD state
Present in the current official mapping
Known exploitation
Recorded by ENISA since 3 Nov 2021. Evidence sources: cisa_kev.
ENISA score
9.1 · CVSS 3.1
Advisory evidence
1 linked advisory record
Recommended actionPatch now

CISA confirms exploitation in the wild and lists 2021-11-17 as the remediation due date.

Patch available
01

What, why and how

Microsoft Exchange Server contains an unspecified vulnerability that allows for remote code execution.

What

Microsoft Exchange Server contains an unspecified vulnerability that allows for remote code execution.

Why

The server follows an attacker-influenced destination, allowing requests to systems or services the attacker cannot reach directly.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may execute code or commands in the affected security context.

What

Microsoft Exchange Server contains an unspecified vulnerability that allows for remote code execution.

Why

The server follows an attacker-influenced destination, allowing requests to systems or services the attacker cannot reach directly.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may execute code or commands in the affected security context.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
Confirmed in the wild

CISA added this CVE to its Known Exploited Vulnerabilities catalogue on 2021-11-03. Known ransomware campaign use is recorded.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
Reference recorded

A structured CVE source labels at least one public reference as exploit material. BlackTree has not independently validated that it is safe, reliable or weaponised.

Likely attack path
a network path → Server-Side Request Forgery (SSRF) → execute code or commands in the affected security context
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Unchanged: impact remains within the vulnerable component's security authority
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-918 ↗

CWE-918: Server-Side Request Forgery (SSRF). The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N/E:U/RL:O/RC:C

Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.

AVNetworkAttack vector: The vulnerable component can be reached over a network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CHighConfidentiality impact: A successful attack can cause a major loss.IHighIntegrity impact: A successful attack can cause a major loss.ANoneAvailability impact: No direct loss is represented by this metric.
Post-exploitation / living off the land
After compromise, an attacker may use built-in shells, scripting engines, scheduled tasks and native network utilities for discovery, persistence or movement. This is a plausible LoTL path, not evidence that it has occurred for every attack.
NetworkUnauthenticatedRemote code executionCWE-918CISA KEVPublic exploit reference
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

ENISA EUVD · EUVD-2021-21128Known-exploited evidence recorded

Microsoft Exchange Server Remote Code Execution Vulnerability

Official EUVD record ↗
BSI · German · WID-SEC-2024-1897Microsoft Exchange Server: Mehrere Schwachstellen

Ein entfernter, anonymer Angreifer kann mehrere Schwachstellen in Microsoft Exchange Server 2013, Microsoft Exchange Server 2016 und Microsoft Exchange Server 2019 ausnutzen, um beliebigen Programmcode auszuführen, um seine Privilegien zu erhöhen und um Informationen offenzulegen.

Official advisory ↗
Canadian Centre for Cyber Security · English · AL21-017Ongoing Exploitation of ProxyShell Exploit Chain

The Cyber Centre is aware of ongoing scanning and exploitation of the ProxyShell exploit chain affecting unpatched Microsoft Exchange Servers. Microsoft has previously released updates to remediate these vulnerabilities in April and May of 2021.

Official advisory ↗
Cyber Security Agency of Singapore · English · CSA-SB-20210721Security Bulletin 21 Jul 2021

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 21 Jul 2021, published on 21 July 2021. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
CERT-FR · French · CERTFR-2021-AVI-522Multiples vulnérabilités dans les produits Microsoft

d?id=CVE-2021-33768 Référence CVE CVE-2021-33775 https://www.cve.org/CVERecord?id=CVE-2021-33775 Référence CVE CVE-2021-33776 https://www.cve.org/CVERecord?id=CVE-2021-33776 Référence CVE CVE-2021-33777 https://www.cve.org/CVERecord?id=CVE-2021-33777 Référence CVE CVE-2021-33778 https://www.cve.org/CVERecord?id=CVE-2021-33778 Référence CVE CVE-2021-34452 https://www.cve.org/CVERecord?id=CVE-2021-34452 Référence CVE CVE-2021-34464 https://www.cve.org/CVERecord?id=CVE-2021-34464 Référence CVE CVE-2021-34469 https://www.cve.org/CVERecord?id=CVE-2021-34469 Référence CVE CVE-2021-34470 https://www.cve.org/CVERecord?id=CVE-2021-34470 Référence CVE CVE-2021-34473 https://www.cve.org/CVERecord?id=CVE-2021-34473 Référence CVE CVE-2021-34474 https://www.cve.org/CVERecord?id=CVE-2021-34474 Référence CVE CVE-2021-34479 https://www.cve.org/CVERecord?id=CVE-2021-34479 Référence CVE CVE-2021-34501 https://www.cve.org/CVERecord?id=CVE-2021-34501 Référence CVE CVE-2021-34522 https://www.cve.org/CVERecord?id=CVE-2021-34522 Référence CVE CVE-2021-34523 https://www.cve.org/CVERecord?id=CVE-2021-34523 Référence CVE CVE-2021-34528 https://www.cve.org/CVERecord?id=CVE-2021-34528 Référence CVE CVE-2021-34529 https://www.cve.org/CVERecord?id=CVE-2021-34529 Gestion détaillée du document le 15 juillet 2021 Version initi

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-002172Microsoft Exchange Server におけるリモートでコードを実行される脆弱性

Microsoft Exchange Server には、リモートでコードを実行される脆弱性が存在します。 本脆弱性は、CVE-2021-31196 および CVE-2021-31206 とは異なる脆弱性です。

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-002110Microsoft Exchange Server におけるリモートでコードを実行される脆弱性

Microsoft Exchange Server には、リモートでコードを実行される脆弱性が存在します。 本脆弱性は、CVE-2021-31196 および CVE-2021-34473 とは異なる脆弱性です。

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-002109Microsoft Exchange Server におけるリモートでコードを実行される脆弱性

Microsoft Exchange Server には、リモートでコードを実行される脆弱性が存在します。 本脆弱性は、CVE-2021-31206 および CVE-2021-34473 とは異なる脆弱性です。

Official advisory ↗
KISA KrCERT/CC · Korean · KNVD-5365MS Exchange Server ProxyShell 취약점 보안 업데이트 권고

Exhcange Server에서 발생하는 원격코드실행 취약점(CVE-2021-34473) [2]

Official advisory ↗
KISA KrCERT/CC · Korean · KNVD-5338MS 7월 보안 위협에 따른 정기 보안 업데이트 권고

al.msrc.microsoft.com/ko-kr/security-guidance [2] (영문) https://portal.msrc.microsoft.com/en-us/security-guidance [3] https://msrc.microsoft.com/update-guide/releaseNote/2021-Jul [4] https://msrc.microsoft.com/update-guide o 취약점 요약 정보 제품 카테고리 CVE 번호 CVE 제목 Active Directory Federation Services CVE-2021-33779 Windows ADFS 보안 기능 우회 취약성 Common Internet File System CVE-2021-34476 Bowser.sys 서비스 거부 취약성 Dynamics Business Central Control CVE-2021-34474 Dynamics Business Central 원격 코드 실행 취약성 Microsoft Bing CVE-2021-33753 Microsoft Bing Search 스푸핑 취약성 Microsoft Exchange Server CVE-2021-34523 Microsoft Exchange Server 권한 상승 취약성 Microsoft Exchange Server CVE-2021-34473 Microsoft Exchange Server 원격 코드 실행 취약성 Microsoft Exchange Server CVE-2021-34470 Microsoft Exchange Server 권한 상승 취약성 Microsoft Exchange Server CVE-2021-33768 Microsoft Exchange Server 권한 상승 취약성 Microsoft Exchange Server CVE-2021-33766 Microsoft Exchange 정보 유출 취약성 Microsoft Exchange Server CVE-2021-31206 Microsoft Exchange Server 원격 코드 실행 취약성 Microsoft Exchange Server CVE-2021-31196 Microsoft Exchange Server 원격 코드 실행 취약성 Microsoft Graphics Component CVE-2021-34498 Windows GDI 권한 상승 취약성 Microsoft Graphics Component CVE-2021-34496 Windows GDI 정보 유출 취약성 Microsoft Graphics Component CVE-2021-34489 DirectWrite 원격 코드 실행 취약성 Microsoft Graphics Compon

Official advisory ↗
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Patch available
Affected
Fixed
An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
Action
Review the linked authoritative reference and apply the recorded fixed release appropriate to the affected product branch.
Workaround
No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04

Evidence and provenance

Published 14 Jul 2021 · Last source change 10 Aug 2026, 15:11 UTC · CWE-918 · Server-Side Request Forgery (SSRF)

CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2021-21128
Product sourceCISA KEV
Remediation sourceCVE/CNA references
CWE sourceCISA ADP
NVD statusNVD enriched

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates ↗
  1. Affected versionsThe structured affected or fixed version information changed.
    Before
    15.00.0 < 15.00.1497.015; 15.01.0 < 15.01.2176.012; 15.01.0 < 15.01.2242.008; 15.02.0 < 15.02.0792.013; 15.02.0 < 15.02.0858.010 · Fixed: An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
    After
    Microsoft Exchange Server 2013 Cumulative Update 23: 15.00.0 < 15.00.1497.015; Microsoft Exchange Server 2016 Cumulative Update 19: 15.01.0 < 15.01.2176.012; Microsoft Exchange Server 2016 Cumulative Update 20: 15.01.0 < 15.01.2242.008; Microsoft Exchange Server 2019 Cumulative Update 8: 15.02.0 < 15.02.0792.013; Microsoft Exchange Server 2019 Cumulative Update 9: 15.02.0 < 15.02.0858.010 · Fixed: An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
    CNA ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Added to CISA KEV
Fixed release or patch reference recorded
ENISA EUVD · EUVD-2021-21128↗CISA KEV record↗CVE authority or vendor reference↗Patch or update reference↗Public exploit reference↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2021-34473 · cve.blacktree.nl