CVE-2021-4040Network attack vector

Denial of service via unchecked XID lengths

Published Aug 24, 2022 · Updated Aug 3, 2024

Denial of service in Red Hat AMQ Broker 7.9.0 and earlier allows remote attackers to interrupt broker availability with crafted messages. The XidCodecSupport decoder allocates branch-qualifier and global-transaction byte arrays directly from attacker-declared lengths without checking the readable buffer size. Network access to a broker acceptor is sufficient; sustained malicious messages can exhaust JVM memory and partially interrupt message delivery.

CVSS severity5.3
Medium
EPSS probability3.13%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Red Hat AMQ Broker 7.9.0 and earlier allows remote attackers to interrupt broker availability with crafted messages. The XidCodecSupport decoder allocates branch-qualifier and global-transaction byte arrays directly from attacker-declared lengths without checking the readable buffer size. Network access to a broker acceptor is sufficient; sustained malicious messages can exhaust JVM memory and partially interrupt message delivery.

The record

CVE
CVE-2021-4040
Published
Aug 24, 2022
Updated
Aug 3, 2024
Vendor
389 Directory Server
Product
Red Hat AMQ Broker
Classifications
CWE-400, CWE-787, T1499.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 24, 2022CVE 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=Fixed in v2.19.1, v2.20.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

389 Directory Server · Red Hat AMQ Brokerversion=Fixed in v2.19.1, v2.20.0

Published CVSS scores

5.3NIST National Vulnerability DatabaseCVSS:3.1/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 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-400Uncontrolled Resource Consumption
CWE-787Out-of-bounds Write
T1499.002Service Exhaustion Flood

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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