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Fencer Vulns
high 7.5

CVE-2021-30639 json

DoS after non-blocking IO error

published 2021-07-12 5 y ago modified 2026-09-08 2 mo ago also BIT-tomcat-2021-30639 , EUVD-2021-1554 , GHSA-44qp-qhfv-c7f6

cvss
7.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
6.9%
EPSS 6.9% chance of exploitation in 30 days, percentile 94%
public exploits
0
none known

Summary

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.

Patch / fix

  • maven org.apache.tomcat:tomcat 8.5.65, 9.0.45, 10.0.5
  • bitnami tomcat 8.5.65, 9.0.45, 10.0.4, 10.0.5
  • mcafee epolicy_orchestrator 5.10.0
  • oracle big_data_spatial_and_graph 23.1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-30639 updated cvss 7.5

tomcat: non-blocking I/O error flag is not reset between requests

  • Red Hat OpenStack Platform 10 (Newton) opendaylight Red Hat OpenStack Platform 13 (Queens) opendaylight
    affected: no fix planned “Out of support scope”
  • Red Hat Decision Manager 7 tomcat Red Hat Enterprise Linux 6 tomcat6, tomcat6-lib, tomcat6-log4j, tomcat6-javadoc, tomcat6-webapps, tomcat6-el-2.1-api, +4 more Red Hat Enterprise Linux 7 tomcat, tomcat-lib, tomcat-jsvc, tomcat-javadoc, tomcat-webapps, tomcat-el-2.2-api, +4 more Red Hat Enterprise Linux 8 pki-servlet-engine, pki-servlet-4.0-api Red Hat Enterprise Linux 9 tomcat, tomcat-lib, tomcat-webapps, tomcat-el-3.0-api, tomcat-docs-webapp, tomcat-jsp-2.3-api, +2 more Red Hat Fuse 7 tomcat
    +8 more products
    Red Hat JBoss Data Grid 6 jbossweb jbossweb Red Hat JBoss Data Virtualization 6 jbossweb jbossweb Red Hat JBoss Enterprise Application Platform 6 jbossweb jbossweb Red Hat JBoss Fuse 6 tomcat Red Hat JBoss Web Server 3 tomcat Red Hat JBoss Web Server 5 tomcat Red Hat Process Automation 7 tomcat Red Hat support for Spring Boot tomcat
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

6.89% chance of exploitation in the next 30 days, higher than 94% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
GitHub 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD 2.0 5.0 AV:N/AC:L/Au:N/C:N/I:N/A:P
OSV 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
maven org.apache.tomcat:tomcat
>=10.0.3, <10.0.5
>=9.0.0, <9.0.45
<8.5.65
10.0.5
9.0.45
8.5.65
bitnami tomcat
>=8.5.64, <8.5.65
>=9.0.44, <9.0.45
>=10.0.3, <10.0.4
>=10.0.4, <10.0.5
8.5.65
9.0.45
10.0.4
10.0.5

Affected products

  • Apache Software Foundation Apache Tomcat

Classification

Weakness
  • CWE-755 Improper Handling of Exceptional Conditions

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.