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Vulnerabilities

Vulnerability · CVE-2021-30639

A vulnerability in Apache Tomcat allows an attacker to remotely trigger a denial of service.

Published Jul 12, 2021 · catalog updated Jun 17, 2026 · A vulnerability in Apache

Last checked Nov 6, 2026. A connected source was read within the last 7 days.

Check if you run it

No confirmed exploitation is on record for CVE-2021-30639. EPSS is 6.89%. Act only if a listed version of A vulnerability in Apache is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (A vulnerability in Apache).
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.

Same product and reporting

Severity
High7.5
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
6.89%
Remediation
Version ranges on file
Affected products
cpe apache/tomcat · cpe mcafee/epolicy orchestrator

A vulnerability in Apache Tomcat allows an attacker to remotely trigger a denial of service. An error introduced as part of a change to improve error handling during non-blocking I/O meant that the error flag associated with the Request object was not reset between requests. This meant that once a non-blocking I/O error occurred, all future requests handled by that request object would fail. Users were able to trigger non-blocking I/O errors, e.g. by dropping a connection, thereby creating the possibility of triggering a DoS. Applications that do not use non-blocking I/O are not exposed to this vulnerability. This issue affects Apache Tomcat 10.0.3 to 10.0.4; 9.0.44; 8.5.64.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe apache/tomcat10.0.3
  • cpe apache/tomcat10.0.4
  • cpe apache/tomcat8.5.64
  • cpe apache/tomcat9.0.44
  • cpe mcafee/epolicy orchestrator5.10.0
  • cpe mcafee/epolicy orchestrator< 5.10.0

How to fix CVE-2021-30639

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2021-30639. EPSS is 6.89%. Act only if a listed version of A vulnerability in Apache is installed.

Which versions are affected?

Compare what you have installed with mcafee/epolicy orchestrator 5.10.0; mcafee/epolicy orchestrator < 5.10.0. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-755: Improper Handling of Exceptional Conditions. EPSS 6.89%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Technology hubs

Apache Tomcat security

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. Jul 12, 2021 · Monitored products — critical

    Detected

    A vulnerability in Apache Tomcat allows an attacker to remotely trigger a denial of service. An error introduced as part of a change to improve error handling during non-blocking I/O meant that the error flag associated with the Request object was not reset between requests. This meant that once a non-blocking I/O error occurred, all future requests handled by that request object would fail. Users

  2. Jun 17, 2026 · Monitored products — critical

    Updated

    A vulnerability in Apache Tomcat allows an attacker to remotely trigger a denial of service. An error introduced as part of a change to improve error handling during non-blocking I/O meant that the error flag associated with the Request object was not reset between requests. This meant that once a non-blocking I/O error occurred, all future requests handled by that request object would fail. Users

Sources

  • CVE.orgVulnerability recordCVE-2021-30639

    Official CVE identifier

    cve.org
  • Monitored products — criticalVendor advisoryCVE-2021-30639

    A vulnerability in Apache Tomcat allows an attacker to remotely trigger a denial of service. An error introduced as part of a change to improve error handling during non-blocking I/O meant that the error flag associated with the Request object was not reset between requests. This meant that once a non-blocking I/O error occurred, all future requests handled by that request object would fail. Users

    nvd.nist.gov

References

Freshness

Last verified in this catalog Nov 6, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.

  • CVE.orgNov 4, 2026
  • Monitored products — criticalNov 3, 2026