CVE-2021-20838Network attack vector

Conversion hang via unrestricted XML entity processing

Published Nov 1, 2021 · Updated Aug 3, 2024

XXE in Office Server Document Converter 7.2MR4 and earlier and 7.1MR7 and earlier allows remote attackers to exhaust server resources. During Office-document conversion, the XML parser resolves entity references in embedded crafted XML, causing processing not to terminate and resource use to grow. No authentication or user interaction is required; the bounded impact is a hung conversion process and resource exhaustion on the server.

CVSS severity5.3
Medium
EPSS probability1.52%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

XXE in Office Server Document Converter 7.2MR4 and earlier and 7.1MR7 and earlier allows remote attackers to exhaust server resources. During Office-document conversion, the XML parser resolves entity references in embedded crafted XML, causing processing not to terminate and resource use to grow. No authentication or user interaction is required; the bounded impact is a hung conversion process and resource exhaustion on the server.

The record

CVE
CVE-2021-20838
Published
Nov 1, 2021
Updated
Aug 3, 2024
Vendor
Antenna House, Inc.
Product
Office Server Document Converter
Classifications
CWE-611, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 1, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record 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=V7.2MR4 and earlier and V7.1MR7 and earlier

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Antenna House, Inc. · Office Server Document Converterversion=V7.2MR4 and earlier and V7.1MR7 and earlier

Published CVSS scores

5.0JPCERT/CC and IPAAV:N/AC:L/Au:N/C:N/I:N/A:P
5.3JPCERT/CC and IPACVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-611Improper Restriction of XML External Entity Reference
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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

Technologies

Your stack

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Your stack

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