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Full vulnerability report · 2021
CVE-2021-26412High confidence

Microsoft Exchange Server Remote Code Execution Vulnerability

Microsoft · Microsoft Exchange Server 2013 Cumulative Update 23

9.1CriticalCVSS 3.1
Recommended action
Within 72 hours

Critical technical impact and a public exploit reference; no CISA KEV confirmation is currently recorded.

Patch available
R
Operational reassessment

Published severity in operational context

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

Evidence used

  • No CISA KEV confirmation is currently recorded.
  • A structured source references public exploit or proof-of-concept material.
  • EPSS is 33.76% 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 Microsoft Exchange Server 2013 Cumulative Update 23 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-2021-13218

No EUVD known-exploited evidence

Microsoft Exchange Server Remote Code Execution Vulnerability

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
9.1 · CVSS 3.1
Advisory evidence
No linked advisory details stored yet
Recommended actionWithin 72 hours

Critical technical impact and a public exploit reference; no CISA KEV confirmation is currently recorded.

Patch available
01

What, why and how

Microsoft Exchange Server Remote Code Execution Vulnerability

What

Microsoft Exchange Server Remote Code Execution Vulnerability

Why

The current structured CVE record identifies a security weakness, but the root cause requires confirmation in the linked vendor material.

How

An attacker operating through a network path may attempt exploitation with elevated privileges. If successful, the issue may execute code or commands in the affected security context.

What

Microsoft Exchange Server Remote Code Execution Vulnerability

Why

The current structured CVE record identifies a security weakness, but the root cause requires confirmation in the linked vendor material.

How

An attacker operating through a network path may attempt exploitation with elevated privileges. 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.
No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

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

CISA Vulnrichment records proof-of-concept exploitation in its SSVC data. BlackTree has not independently executed or validated exploit material.

Likely attack path
a network path → vulnerable operation → execute code or commands in the affected security context
Attack surface
Network
Privileges required
High: elevated access is required
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Changed: exploitation can affect a different security authority
Weakness
?CWE means Common Weakness Enumeration.
CWE not yet assigned
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:H/UI:N/S:C/C:H/I:H/A:H/E:P/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.PRHighPrivileges required: The attacker needs elevated or administrative privileges.UINoneUser interaction: No action by another user is required.SChangedScope: The attack can affect a component governed by a different security authority.CHighConfidentiality impact: A successful attack can cause a major loss.IHighIntegrity impact: A successful attack can cause a major loss.AHighAvailability impact: A successful attack can cause a major loss.
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.
NetworkRemote code executionPublic exploit reference
A

Official authority intelligence

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

ENISA EUVD · EUVD-2021-13218Official EUVD mapping

Microsoft Exchange Server Remote Code Execution Vulnerability

Official EUVD record ↗
Cyber Security Agency of Singapore · English · CSA-SB-20210310Security Bulletin 10 Mar 2021

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 10 Mar 2021, published on 10 March 2021. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
CERT-FR · French · CERTFR-2021-AVI-156Multiples vulnérabilités dans Microsoft Exchange Server

De multiples vulnérabilités ont été découvertes dans Microsoft Exchange Server. Elles permettent à un attaquant de provoquer une exécution de code arbitraire à distance.

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-001172Microsoft 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-2021-26412、CVE-2021-26854、CVE-2021-26855、CVE-2021-26857、CVE-2021-26858、CVE-2021-27065 とは異なる脆弱性です。

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-001133Microsoft 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-2021-26412、CVE-2021-26854、CVE-2021-26857、CVE-2021-26858、CVE-2021-27065、CVE-2021-27078 とは異なる脆弱性です。

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-001131Microsoft 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-2021-26854、CVE-2021-26855、CVE-2021-26857、CVE-2021-26858、CVE-2021-27065、CVE-2021-27078 とは異なる脆弱性です。

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-001171Microsoft 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-2021-26412、CVE-2021-26854、CVE-2021-26855、CVE-2021-26857、CVE-2021-26858、CVE-2021-27078 とは異なる脆弱性です。

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-001170Microsoft 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-2021-26412、CVE-2021-26854、CVE-2021-26855、CVE-2021-26857、CVE-2021-27065、CVE-2021-27078 とは異なる脆弱性です。

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-001169Microsoft 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-2021-26412、CVE-2021-26854、CVE-2021-26855、CVE-2021-26858、CVE-2021-27065、CVE-2021-27078 とは異なる脆弱性です。

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-001132Microsoft 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-2021-26412、CVE-2021-26855、CVE-2021-26857、CVE-2021-26858、CVE-2021-27065、CVE-2021-27078 とは異なる脆弱性です。

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 2 Mar 2021 · Last source change 19 Aug 2026, 16:30 UTC · CWE not yet assigned

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-2021-13218
Product sourceCNA
Remediation sourceCVE/CNA references
CWE sourceUnavailable
NVD statusNVD modified after enrichment

Missing structured fields: CWE classification. Missing data is not evidence of low risk; review the primary advisory.

Material change intelligence

What changed after publication

View recent updates ↗
  1. Vendor guidanceAuthoritative vendor guidance changed: added remediation: portal.msrc.microsoft.com/CVE-2021-26412; removed patch: msrc.microsoft.com/CVE-2021-26412; removed remediation: msrc.microsoft.com/CVE-2021-26412.
    Before
    patch: msrc.microsoft.com/CVE-2021-26412 · patch: portal.msrc.microsoft.com/CVE-2021-26412 · remediation: msrc.microsoft.com/CVE-2021-26412
    After
    patch: portal.msrc.microsoft.com/CVE-2021-26412 · remediation: portal.msrc.microsoft.com/CVE-2021-26412
    portal.msrc.microsoft.com ↗
  2. Vendor guidanceAuthoritative vendor guidance changed: added patch: msrc.microsoft.com/CVE-2021-26412; added remediation: msrc.microsoft.com/CVE-2021-26412; removed remediation: portal.msrc.microsoft.com/CVE-2021-26412.
    Before
    patch: portal.msrc.microsoft.com/CVE-2021-26412 · remediation: portal.msrc.microsoft.com/CVE-2021-26412
    After
    patch: msrc.microsoft.com/CVE-2021-26412 · patch: portal.msrc.microsoft.com/CVE-2021-26412 · remediation: msrc.microsoft.com/CVE-2021-26412
    msrc.microsoft.com ↗
  3. Affected versionsThe structured affected or fixed version information changed.
    Before
    15.00.0 < publication; 15.02.0 < publication; 15.01.0 < publication · 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
    15.00.0 < 15.00.1497.012; 15.01.0 < 15.01.2106.013; 15.01.0 < 15.01.2176.009; 15.02.0 < 15.02.0721.013; 15.02.0 < 15.02.0792.010 · 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
Fixed release or patch reference recorded
ENISA EUVD · EUVD-2021-13218↗CISA Vulnrichment SSVC evidence↗Patch or update reference↗CVE authority or vendor 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-2021-26412 · cve.blacktree.nl