LiveActive security incident?Get immediate response
CVE Record

CVE-2021-30639: DoS after non-blocking IO error

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.

UnknownCVSS not scoredNot KEV-listedUpdated
Discuss exposureBack to CVEs
Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

This Apache Tomcat flaw can let a remote user cause service disruption in specific Tomcat releases. The issue is not described as data theft or code execution. Exposure depends on using non-blocking I/O; applications that do not use it are not exposed according to the CVE description.

Executive priority

Treat this as a service availability risk for affected Tomcat deployments. Prioritize internet-facing or business-critical applications first, especially where non-blocking I/O is enabled. Urgency is lower than a confirmed exploited code-execution issue.

Technical view

A Request object's error flag was not reset after a non-blocking I/O error. If a user triggered such an error, for example by dropping a connection, later requests handled by that object could fail, creating a denial-of-service condition in affected Tomcat versions.

Likely exposure

Exposure is limited to Apache Tomcat 10.0.3-10.0.4, 9.0.44, and 8.5.64 deployments that use non-blocking I/O. Systems not using non-blocking I/O are described as not exposed.

Exploitation context

The source bundle says the condition can be remotely triggered by causing non-blocking I/O errors, such as dropping a connection. KEV is false, and the provided sources do not state active exploitation.

Researcher notes

The bundle provides affected versions and root cause but no CVSS vector, CWE, exact fixed versions, or exploit-in-the-wild evidence. Do not assume exposure without confirming non-blocking I/O use.

Mitigation direction

  • Inventory Tomcat versions and identify the listed affected releases.
  • Confirm whether affected applications use non-blocking I/O.
  • Review Apache and downstream vendor advisories for fixed release guidance.
  • Upgrade or remediate according to Apache or product-vendor instructions.
  • Monitor availability and request-failure rates until remediation is complete.

Validation and detection

  • Verify running Tomcat version against the affected version list.
  • Confirm application or connector use of non-blocking I/O.
  • Review logs for dropped connections followed by repeated request failures.
  • Validate service stability after applying vendor-directed remediation.
Prepared
Confidence
high
Sources
9

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cve · low confidence lookup

CVE-2021-30639 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

Open ATT&CK lookup
Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
0Timeline events
0ADP providers
8Source links

CVSS and timeline data

No CVSS vectors or timeline events were available in the normalized CVE source material.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
Apache Software FoundationApache TomcatApache Tomcat 10 10.0.3 to 10.0.4, Apache Tomcat 9 9.0.44, Apache Tomcat 8.5 8.5.64Listed
Weakness

CWE details

No CWE listed

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.