CVE-2021-23926Network attack vector

Denial of service via recursive entity expansion

Published Jan 14, 2021 · Updated Feb 13, 2025

XML entity expansion in Apache XMLBeans 2.6.0 and earlier allows remote attackers to exhaust memory by parsing crafted XML. The XMLBeans-created parser leaves DTD entity-expansion security properties unset, so recursive entities expand exponentially. An application must pass attacker-controlled XML to the library; successful exploitation can hang or crash that application through resource exhaustion.

CVSS severity9.1
Critical
EPSS probability6.21%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

XML entity expansion in Apache XMLBeans 2.6.0 and earlier allows remote attackers to exhaust memory by parsing crafted XML. The XMLBeans-created parser leaves DTD entity-expansion security properties unset, so recursive entities expand exponentially. An application must pass attacker-controlled XML to the library; successful exploitation can hang or crash that application through resource exhaustion.

The record

CVE
CVE-2021-23926
Published
Jan 14, 2021
Updated
Feb 13, 2025
Vendor
The Apache Software Foundation
Product
Apache XMLBeans
Classifications
CWE-776, CAPEC-197, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 14, 2021CVE publishedPublication date reported by the CVE source.
  2. Feb 13, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=Apache XMLBeans <=2.6.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Apache Software Foundation · Apache XMLBeansversion=Apache XMLBeans <=2.6.0

Published CVSS scores

9.1GitHub Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-776Improper Restriction of Recursive Entity References in DTDs ('XML Entity Expansion')
CAPEC-197Exponential Data Expansion
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

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo