CVE-2021-31207Known exploitationPublic exploitNetwork attack vector

Arbitrary file write via crafted PST export

Published May 11, 2021 · Updated Oct 21, 2025

Path traversal in Microsoft Exchange Server allows remote authenticated users to write files outside the intended PST export path. New-MailboxExportRequest accepts a crafted export filename and decodes embedded mailbox content while writing the PST as a web-executable file. Exploitation requires mailbox-export privileges; placing the resulting file in a web directory enables web-shell execution.

CVSS severity6.6
Medium
EPSS probability99.78%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Path traversal in Microsoft Exchange Server allows remote authenticated users to write files outside the intended PST export path. New-MailboxExportRequest accepts a crafted export filename and decodes embedded mailbox content while writing the PST as a web-executable file. Exploitation requires mailbox-export privileges; placing the resulting file in a web directory enables web-shell execution.

The record

CVE
CVE-2021-31207
Published
May 11, 2021
Updated
Oct 21, 2025
Vendor
Microsoft
Product
Microsoft Exchange Server 2013 Cumulative Update 23
Classifications
CWE-22, T1505.003
Attack vector
network
Privileges
admin

Timeline

How it unfolded

  1. May 11, 2021CVE publishedPublication date reported by the CVE source.
  2. Oct 21, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=15.00.0 <15.00.1497.018

What conditions does exploitation require?

Attack vectornetwork
Required privilegesadmin

What is affected?

Microsoft · Microsoft Exchange Server 2013 Cumulative Update 23version=15.00.0 <15.00.1497.018
Microsoft · Microsoft Exchange Server 2016 Cumulative Update 19version=15.01.0 <15.01.2176.014
Microsoft · Microsoft Exchange Server 2019 Cumulative Update 8version=15.02.0 <15.02.0792.015
Microsoft · Microsoft Exchange Server 2019 Cumulative Update 9version=15.02.0 <15.02.0858.012
Microsoft · Microsoft Exchange Server 2016 Cumulative Update 20version=15.01.0 <15.01.2242.010

Published CVSS scores

6.6MicrosoftCVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
7.2NIST NVDCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesadmin
Known exploitationReported
Public exploitPublished

Weakness, pattern, technique

CWE-22Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
T1505.003Server Software Component: Web Shell

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Reported exploitation

Technologies

Your stack

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Your stack

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