CVE-2021-30639Network attack vector

Service interruption via persistent request error flag

Published Jul 12, 2021 · Updated Aug 3, 2024

Improper error handling in Apache Tomcat 10.0.3 through 10.0.4, 9.0.44, and 8.5.64 allows remote attackers to interrupt service. The Request object retains its error flag after a non-blocking I/O error, causing later requests assigned to that reused object to fail. Only applications using non-blocking I/O are exposed; dropping a connection can poison a reused Request object and disrupt subsequent traffic.

CVSS severity7.5
High
EPSS probability6.89%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper error handling in Apache Tomcat 10.0.3 through 10.0.4, 9.0.44, and 8.5.64 allows remote attackers to interrupt service. The Request object retains its error flag after a non-blocking I/O error, causing later requests assigned to that reused object to fail. Only applications using non-blocking I/O are exposed; dropping a connection can poison a reused Request object and disrupt subsequent traffic.

The record

CVE
CVE-2021-30639
Published
Jul 12, 2021
Updated
Aug 3, 2024
Vendor
The Apache Software Foundation
Product
Apache Tomcat
Classifications
CWE-755, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 12, 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=Apache Tomcat 10 10.0.3 to 10.0.4
  2. Affected versionversion=Apache Tomcat 8.5 8.5.64
  3. Affected versionversion=Apache Tomcat 9 9.0.44

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Apache Software Foundation · Apache Tomcatversion=Apache Tomcat 10 10.0.3 to 10.0.4; version=Apache Tomcat 8.5 8.5.64; version=Apache Tomcat 9 9.0.44

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
5.0NIST NVDAV:N/AC:L/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-755Improper Handling of Exceptional Conditions
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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