CVE-2021-40439Network attack vector

Denial of service via nested XML entities

Published Oct 7, 2021 · Updated Aug 4, 2024

XML entity expansion in Apache OpenOffice 4.1.10 and earlier allows remote attackers to exhaust resources via a crafted ODF file. The bundled Expat parser recursively materializes nested entity replacements from an ODF member XML file without an effective resource bound. A user must open the attacker-supplied document, after which resource consumption can hang or crash the application; no confidentiality or integrity impact is reported.

CVSS severity6.5
Medium
EPSS probability3.87%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

XML entity expansion in Apache OpenOffice 4.1.10 and earlier allows remote attackers to exhaust resources via a crafted ODF file. The bundled Expat parser recursively materializes nested entity replacements from an ODF member XML file without an effective resource bound. A user must open the attacker-supplied document, after which resource consumption can hang or crash the application; no confidentiality or integrity impact is reported.

The record

CVE
CVE-2021-40439
Published
Oct 7, 2021
Updated
Aug 4, 2024
Vendor
The Apache Software Foundation
Product
Apache OpenOffice
Classifications
CWE-611, T1499, T1204.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 7, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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=Apache OpenOffice <=4.1.10
  2. Affected versionversion=OpenOffice.org <=3.4

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Apache Software Foundation · Apache OpenOfficeversion=Apache OpenOffice <=4.1.10; version=OpenOffice.org <=3.4

Published CVSS scores

6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:N/A:P

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
T1499Endpoint Denial of Service
T1204.002Malicious File

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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