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NVD / CVE Program· CNA apache

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

Noroxi assessment

Priority: Monitor (action score 32/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 6.8% (FIRST EPSS); higher than 94% of all records.
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: org.apache.tomcat:tomcat (Maven) 10.0.5, 9.0.45, 8.5.65.
  • Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to org.apache.tomcat:tomcat (Maven) 10.0.5, 9.0.45, 8.5.65 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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.

HighCVSS 7.5 · v3.1—No exploit Fix available
Published
Jul 12, 2021
Updated
Jun 16, 2026
EPSS
6.8% · 94th percentile

Report tools

JSON

Action score

32

Monitor

Low priority for now.

CVSS
30 / 40 · 7.5 / 10
CISA KEV
0 / 30 · Not listed
EPSS
2 / 30 · 6.8%

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

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When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
apachetomcat
mcafeeepolicy orchestrator
oraclebig data spatial and graph

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • apache tomcat10.0.3
  • apache tomcat10.0.4
  • apache tomcat8.5.64
  • apache tomcat9.0.44
  • mcafee epolicy orchestratorbefore 5.10.0
  • mcafee epolicy orchestrator5.10.0
  • oracle big data spatial and graphbefore 23.1

Versions reported by the vendor

Affected version ranges reported by the assigning authority (apache). Independent of NVD's CPE analysis and usually ahead of it.

  • Apache Software Foundation Apache Tomcat

    • Apache Tomcat 10 10.0.3 to 10.0.4, Apache Tomcat 9 9.0.44, Apache Tomcat 8.5 8.5.64affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Mavenorg.apache.tomcat:tomcatfrom 10.0.3 · before 10.0.510.0.5
Mavenorg.apache.tomcat:tomcatfrom 9.0.0 · before 9.0.459.0.45
Mavenorg.apache.tomcat:tomcatbefore 8.5.658.5.65

Same product

apache: all records

Other highest-scoring records for the same primary product.

  • CVE-2025-24813Apache Tomcat: Potential RCE and/or information disclosure and/or information corruption with partial PUTKEV
    99Now
  • CVE-2016-8735Remote code execution is possible with Apache Tomcat before 6.0.48, 7.x before 7.0.73, 8.x before 8.0.39, 8.5.x before 8.5.7, and 9.x beforeKEV
    96Now
  • CVE-2017-12617When running Apache Tomcat versions 9.0.0.M1 to 9.0.0, 8.5.0 to 8.5.22, 8.0.0.RC1 to 8.0.46 and 7.0.0 to 7.0.81 with HTTP PUTs enabled (e.g.KEV
    92Now

Published before and after this one in the same product

  • ← EarlierCVE-2021-25122Mar 1, 2021 · Apache Tomcat h2c request mix-up
    35Monitor
  • ← EarlierCVE-2021-25329Mar 1, 2021 · Incomplete fix for CVE-2020-9484
    31Monitor
  • Later →CVE-2021-30640Jul 12, 2021 · Auth weakness in JNDIRealm
    29Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Maven:org.apache.tomcat:tomcat10.0.5Package registry (OSV)
Maven:org.apache.tomcat:tomcat8.5.65Package registry (OSV)
Maven:org.apache.tomcat:tomcat9.0.45Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

All national notices →

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
none
Integrity
none
Availability
high · the service can be disrupted
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
None
Integrity impact
None
Availability impact
High

Weakness class (CWE)

CWE-755 · Improper Handling of Exceptional Conditions

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (6 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records