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Full vulnerability report · 2021
CVE-2021-33766High confidence

Microsoft Exchange Server Information Disclosure

Microsoft · Exchange Server

7.3HighCVSS 3.1
Recommended action
Patch now

CISA confirms exploitation in the wild and lists 2022-02-01 as the remediation due date.

Patch available
Optional official sources

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

Select the national-authority views to include. The exact source language is shown on each matched advisory. Your choice is remembered on this device and encoded in the shareable URL.

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-2021-20443

CISA KEV mirrored by ENISA

Microsoft Exchange Server Information Disclosure Vulnerability

EUVD state
Present in the current official mapping
Known exploitation
Recorded by ENISA since 18 Jan 2022. Evidence sources: cisa_kev.
ENISA score
7.3 · CVSS 3.1
Advisory evidence
1 linked advisory record
Recommended actionPatch now

CISA confirms exploitation in the wild and lists 2022-02-01 as the remediation due date.

Patch available
01

What, why and how

Microsoft Exchange Server contains an information disclosure vulnerability which can allow an unauthenticated attacker to steal email traffic from target.

What

Microsoft Exchange Server contains an information disclosure vulnerability which can allow an unauthenticated attacker to steal email traffic from target.

Why

The affected component does not establish the requesting party's identity reliably before granting access.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may obtain information outside the intended access boundary.

What

Microsoft Exchange Server contains an information disclosure vulnerability which can allow an unauthenticated attacker to steal email traffic from target.

Why

The affected component does not establish the requesting party's identity reliably before granting access.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may obtain information outside the intended access boundary.

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 2022-01-18.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path
a network path → Improper Authentication → obtain information outside the intended access boundary
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-287 ↗

CWE-287: Improper Authentication. When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.

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:L/I:L/A:L/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.CLowConfidentiality impact: A successful attack can cause a limited loss.ILowIntegrity impact: A successful attack can cause a limited loss.ALowAvailability impact: A successful attack can cause a limited loss.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
NetworkUnauthenticatedCWE-287CISA KEV
A

Official authority intelligence

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

ENISA EUVD · EUVD-2021-20443Known-exploited evidence recorded

Microsoft Exchange Server Information Disclosure 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 ↗
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

ne élévation de privilèges. Solution Se référer au bulletin de sécurité de l'éditeur pour l'obtention des correctifs (cf. section Documentation). Documentation Bulletin de sécurité Microsoft du 14 juillet 2021 https://msrc.microsoft.com/update-guide/ Référence CVE CVE-2021-31196 https://www.cve.org/CVERecord?id=CVE-2021-31196 Référence CVE CVE-2021-31206 https://www.cve.org/CVERecord?id=CVE-2021-31206 Référence CVE CVE-2021-31947 https://www.cve.org/CVERecord?id=CVE-2021-31947 Référence CVE CVE-2021-31984 https://www.cve.org/CVERecord?id=CVE-2021-31984 Référence CVE CVE-2021-33753 https://www.cve.org/CVERecord?id=CVE-2021-33753 Référence CVE CVE-2021-33766 https://www.cve.org/CVERecord?id=CVE-2021-33766 Référence CVE CVE-2021-33767 https://www.cve.org/CVERecord?id=CVE-2021-33767 Référence CVE CVE-2021-33768 https://www.cve.org/CVERecord?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=

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-002101Microsoft Exchange Server における情報を公開される脆弱性

Microsoft Exchange Server には、情報を公開される脆弱性が存在します。

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

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 Component CVE-2021-34440 GDI+ 정보 유출 취약성 Microsoft Graphics Component CVE-2021-34438 Windows 글꼴 드라이버 호스트 원격 코드 실행 취약성 Microsoft Office CVE-2021-34469 Microsoft Office 보안 기능 우회 취약성 Microsoft Office CVE-2021-34452 Microsoft Word 원격 코드 실행 취약성 M

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-287 · Improper Authentication

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-2021-20443
Product sourceCNA
Remediation sourceCVE/CNA references
CWE sourceCISA KEV
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-2021-20443↗CISA KEV record↗CVE authority or vendor reference↗Patch or update 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-2021-33766 · cve.blacktree.nl