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Full vulnerability report · 2021
CVE-2021-42340High confidence

DoS via memory leak with WebSocket connections

Apache Software Foundation · Apache Tomcat

7.5HighCVSS 3.1
Recommended action
Within 7 days

High technical severity; prioritise exposed affected systems while verifying vendor guidance.

Patch available
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityHighOperational priority:Critical, raised one band.upgradedsince 5 Oct 2026

Evidence used

  • No CISA KEV confirmation is currently recorded.
  • The selected CVSS metric records a network-reachable, unauthenticated path with no user interaction.
  • EPSS is 11.80% for the current model date.

Compensating controls

  • Validate the affected product branch and deploy the verified fixed release.
  • Restrict the affected network interface to trusted sources where business-safe.
  • Monitor vendor guidance and exploitation sources for a material change.

Verification

  1. Confirm that the asset runs Apache Software Foundation Apache Tomcat and falls inside the recorded affected range.
  2. Verify the installed build against the product-specific fixed version after deployment.
  3. Validate exposure, authentication requirements and compensating controls in the actual environment.
  4. Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Mitigation target: Within 3 daysRemediation target: Within 90 days

This automated reassessment organises public evidence. It does not know asset exposure, business impact or control effectiveness and does not replace CVSS or a human risk decision.

Distribution package intelligence

Release-specific package status

Debian findings are scoped to the named distribution, release and source package. An absent finding does not mean a package is unaffected.

4 package states
Repository candidate not checked

A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.

Distribution releaseSource packageVendor stateFixed versionEvidence
Debian trixietrixie · sourcetomcat9Vendor fix publishedDebian records a fixed source-package version for this release.9.0.54-1Debian Security Tracker ↗Source updated 5 Oct 2026
Debian bookwormbookworm · sourcetomcat9Vendor fix publishedDebian records a fixed source-package version for this release.9.0.54-1Debian Security Tracker ↗Source updated 5 Oct 2026
Debian forkyforky · sourcetomcat9Vendor fix publishedDebian records a fixed source-package version for this release.9.0.54-1Debian Security Tracker ↗Source updated 5 Oct 2026
Debian sidsid · sourcetomcat9Vendor fix publishedDebian records a fixed source-package version for this release.9.0.54-1Debian Security Tracker ↗Source updated 5 Oct 2026
Direct vendor intelligence

Authoritative vendor CSAF and VEX advisories

Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.

1 current
CVE-2021-42340 · CSAF 2.0 · revision 3 · finalRed Hat Product Securitytomcat: OutOfMemoryError caused by HTTP upgrade connection leak could lead to DoS
4 known affected

The vendor explicitly identifies these products as affected by this CVE.

  • tomcat as a component of Red Hat JBoss Fuse 6
  • opendaylight.src as a component of Red Hat OpenStack Platform 10 (Newton)
  • opendaylight as a component of Red Hat OpenStack Platform 13 (Queens)
  • opendaylight.src as a component of Red Hat OpenStack Platform 13 (Queens)
Summary
A memory leak flaw was found in Apache Tomcat, where an HTTP upgrade connection does not release for WebSocket connections once the WebSocket connection is closed. If a sufficient number of such requests are made, an OutOfMemoryError occurs, leading to a denial of service. The highest threat from this vulnerability is to system availability.
Remediation
Before applying this update, make sure all previously released errata relevant to your system have been applied. For details on how to apply this update, refer to: https://access.redhat.com/articles/11258
Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Choose official national sources for this report. Each advisory shows its original language. Your selection is remembered on this device and included in shared links.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2021-2266

No EUVD known-exploited evidence

ENISA has published the identifier mapping but no EUVD description has been stored yet.

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
Not supplied in the stored EUVD record
Advisory evidence
No linked advisory details stored yet
Recommended actionWithin 7 days

High technical severity; prioritise exposed affected systems while verifying vendor guidance.

Patch available
01

What, why and how

The fix for bug 63362 present in Apache Tomcat 10.1.0-M1 to 10.1.0-M5, 10.0.0-M1 to 10.0.11, 9.0.40 to 9.0.53 and 8.5.60 to 8.5.71 introduced a memory leak. The object introduced to collect metrics for HTTP upgrade connections was not released for WebSocket connections once the connection was closed. This created a memory leak that, over time, could lead to a denial of service via an OutOfMemoryError.

What

The fix for bug 63362 present in Apache Tomcat 10.1.0-M1 to 10.1.0-M5, 10.0.0-M1 to 10.0.11, 9.0.40 to 9.0.53 and 8.5.60 to 8.5.71 introduced a memory leak. The object introduced to collect metrics for HTTP upgrade connections was not released for WebSocket connections once the connection was closed. This created a memory leak that, over time, could lead to a denial of service via an OutOfMemoryError.

Why

The product does not release a resource after its effective lifetime has ended, i.e., after the resource is no longer needed.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may disrupt the affected service.

What

The fix for bug 63362 present in Apache Tomcat 10.1.0-M1 to 10.1.0-M5, 10.0.0-M1 to 10.0.11, 9.0.40 to 9.0.53 and 8.5.60 to 8.5.71 introduced a memory leak. The object introduced to collect metrics for HTTP upgrade connections was not released for WebSocket connections once the connection was closed. This created a memory leak that, over time, could lead to a denial of service via an OutOfMemoryError.

Why

The product does not release a resource after its effective lifetime has ended, i.e., after the resource is no longer needed.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may disrupt the affected service.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path
a network path → Missing Release of Resource after Effective Lifetime → disrupt the affected service
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Unchanged: impact remains within the vulnerable component's security authority
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-772 ↗

CWE-772: Missing Release of Resource after Effective Lifetime. The product does not release a resource after its effective lifetime has ended, i.e., after the resource is no longer needed.

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.

AVNetworkAttack vector: The vulnerable component can be reached over a network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CNoneConfidentiality impact: No direct loss is represented by this metric.INoneIntegrity impact: No direct loss is represented by this metric.AHighAvailability impact: A successful attack can cause a major loss.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
NetworkUnauthenticatedDenial of serviceCWE-772
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

BSI · German · WID-SEC-2024-1238HPE HP-UX: Mehrere Schwachstellen

Ein anonymer oder lokaler Angreifer kann mehrere Schwachstellen in HPE HP-UX Tomcat Servlet Engine ausnutzen, um Sicherheitsmaßnahmen zu umgehen, einen Denial-of-Service-Zustand zu verursachen, vertrauliche Informationen offenzulegen oder Dateien zu manipulieren.

Official advisory ↗
BSI · German · WID-SEC-2022-1375JFrog Artifactory: Mehrere Schwachstellen

Ein entfernter, anonymer Angreifer kann mehrere Schwachstellen in JFrog Artifactory ausnutzen, um seine Privilegien zu erweitern, beliebigen Code auszuführen, Sicherheitsmaßnahmen zu umgehen, vertrauliche Informationen offenzulegen und einen Denial-of-Service-Zustand auszulösen.

Official advisory ↗
BSI · German · WID-SEC-2022-0607Red Hat FUSE: Mehrere Schwachstellen

Ein entfernter, anonymer, authentisierter oder lokaler Angreifer kann mehrere Schwachstellen in Red Hat FUSE ausnutzen, um vertrauliche Informationen offenzulegen, beliebigen Code auszuführen, einen Denial of Service Zustand herbeizuführen, Sicherheitsmaßnahmen zu umgehen, Daten und Informationen zu manipulieren und seine Privilegien zu erweitern.

Official advisory ↗
BSI · German · WID-SEC-2022-0169Oracle MySQL: Mehrere Schwachstellen

Ein entfernter, anonymer Angreifer kann mehrere Schwachstellen in Oracle MySQL ausnutzen, um die Vertraulichkeit, Integrität und Verfügbarkeit zu gefährden.

Official advisory ↗
BSI · German · WID-SEC-2022-1121Apache Tomcat: Schwachstelle ermöglicht Denial of Service

Ein entfernter, anonymer Angreifer kann eine Schwachstelle in Apache Tomcat ausnutzen, um einen Denial of Service Angriff durchzuführen.

Official advisory ↗
Cyber Security Agency of Singapore · English · CSA-SB-20211020Security Bulletin 20 Oct 2021

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 20 Oct 2021, published on 20 October 2021. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
CERT-FR · French · CERTFR-2024-AVI-0958Multiples vulnérabilités dans les produits IBM

port/pages/node/7175196 Référence CVE CVE-2017-11468 https://www.cve.org/CVERecord?id=CVE-2017-11468 Référence CVE CVE-2017-7500 https://www.cve.org/CVERecord?id=CVE-2017-7500 Référence CVE CVE-2017-7501 https://www.cve.org/CVERecord?id=CVE-2017-7501 Référence CVE CVE-2020-25659 https://www.cve.org/CVERecord?id=CVE-2020-25659 Référence CVE CVE-2020-36242 https://www.cve.org/CVERecord?id=CVE-2020-36242 Référence CVE CVE-2021-35937 https://www.cve.org/CVERecord?id=CVE-2021-35937 Référence CVE CVE-2021-35938 https://www.cve.org/CVERecord?id=CVE-2021-35938 Référence CVE CVE-2021-35939 https://www.cve.org/CVERecord?id=CVE-2021-35939 Référence CVE CVE-2021-42340 https://www.cve.org/CVERecord?id=CVE-2021-42340 Référence CVE CVE-2021-42694 https://www.cve.org/CVERecord?id=CVE-2021-42694 Référence CVE CVE-2021-43618 https://www.cve.org/CVERecord?id=CVE-2021-43618 Référence CVE CVE-2021-43980 https://www.cve.org/CVERecord?id=CVE-2021-43980 Référence CVE CVE-2021-46939 https://www.cve.org/CVERecord?id=CVE-2021-46939 Référence CVE CVE-2021-47018 https://www.cve.org/CVERecord?id=CVE-2021-47018 Référence CVE CVE-2021-47231 https://www.cve.org/CVERecord?id=CVE-2021-47231 Référence CVE CVE-2021-47257 https://www.cve.org/CVERecord?id=CVE-2021-47257 Référence CVE CVE-2021-47284 https://www.cve.org/CVERecord?id=

Official advisory ↗
CERT-FR · French · CERTFR-2024-AVI-0240Multiples vulnérabilités dans les produits IBM

nées. Solution Se référer au bulletin de sécurité de l'éditeur pour l'obtention des correctifs (cf. section Documentation). Documentation Bulletin de sécurité IBM 7144861 du 20 mars 2024 https://www.ibm.com/support/pages/node/7144861 Bulletin de sécurité IBM 7144944 du 21 mars 2024 https://www.ibm.com/support/pages/node/7144944 Référence CVE CVE-2021-22060 https://www.cve.org/CVERecord?id=CVE-2021-22060 Référence CVE CVE-2021-22096 https://www.cve.org/CVERecord?id=CVE-2021-22096 Référence CVE CVE-2021-3923 https://www.cve.org/CVERecord?id=CVE-2021-3923 Référence CVE CVE-2021-41079 https://www.cve.org/CVERecord?id=CVE-2021-41079 Référence CVE CVE-2021-42340 https://www.cve.org/CVERecord?id=CVE-2021-42340 Référence CVE CVE-2022-21216 https://www.cve.org/CVERecord?id=CVE-2022-21216 Référence CVE CVE-2022-22950 https://www.cve.org/CVERecord?id=CVE-2022-22950 Référence CVE CVE-2022-22970 https://www.cve.org/CVERecord?id=CVE-2022-22970 Référence CVE CVE-2022-22971 https://www.cve.org/CVERecord?id=CVE-2022-22971 Référence CVE CVE-2022-22976 https://www.cve.org/CVERecord?id=CVE-2022-22976 Référence CVE CVE-2022-22978 https://www.cve.org/CVERecord?id=CVE-2022-22978 Référence CVE CVE-2022-22980 https://www.cve.org/CVERecord?id=CVE-2022-22980 Référence CVE CVE-2022-25762 https://www.cve.org/CVERecord?id=

Official advisory ↗
CERT-FR · French · CERTFR-2022-AVI-386Multiples vulnérabilités dans IBM QRadar SIEM

d?id=CVE-2021-38869 Référence CVE CVE-2021-38874 https://www.cve.org/CVERecord?id=CVE-2021-38874 Référence CVE CVE-2021-38878 https://www.cve.org/CVERecord?id=CVE-2021-38878 Référence CVE CVE-2021-38919 https://www.cve.org/CVERecord?id=CVE-2021-38919 Référence CVE CVE-2021-38939 https://www.cve.org/CVERecord?id=CVE-2021-38939 Référence CVE CVE-2021-41035 https://www.cve.org/CVERecord?id=CVE-2021-41035 Référence CVE CVE-2021-41182 https://www.cve.org/CVERecord?id=CVE-2021-41182 Référence CVE CVE-2021-41183 https://www.cve.org/CVERecord?id=CVE-2021-41183 Référence CVE CVE-2021-41184 https://www.cve.org/CVERecord?id=CVE-2021-41184 Référence CVE CVE-2021-42340 https://www.cve.org/CVERecord?id=CVE-2021-42340 Référence CVE CVE-2022-22345 https://www.cve.org/CVERecord?id=CVE-2022-22345 Gestion détaillée du document le 26 avril 2022 Version initiale Alertes Avis Bulletins d’actualités Mentions légales Conditions générales À propos Contact cyber.gouv.fr service-public.fr legifrance.gouv.fr info.gouv.fr france.fr info.gouv.fr/risques Premier Ministre / Secrétariat Général de la Défense et de la Sécurité Nationale / Agence nationale de la sécurité des systèmes d'information

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-003083Apache Tomcat におけるサービス運用妨害（DoS）の脆弱性

Apache Tomcat には、サービス運用妨害（DoS）の脆弱性が存在します。 The Apache Software Foundation から、Apache Tomcat の脆弱性に対するアップデートが公開されました。 　* サービス運用妨害（DoS）- CVE-2021-42340 HTTP アップグレード接続のメトリクスを収集するために導入されているオブジェクトが WebSocket 接続が閉じられても解放されずに、メモリリークが発生し、時間経過により OutOfMemoryError となる可能性があります。

Official advisory ↗
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Patch available
Affected
Fixed
Action
Before applying this update, make sure all previously released errata relevant to your system have been applied. For details on how to apply this update, refer to: https://access.redhat.com/articles/11258
Workaround
No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04

Evidence and provenance

Published 14 Oct 2021 · Last source change 4 Aug 2024, 03:30 UTC · CWE-772 · Missing Release of Resource after Effective Lifetime

CVE recordCVE.org · 5.1
CVSS sourceNIST NVD
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2021-2266
Product sourceVendor CSAF · Red Hat Product Security
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceCNA
NVD statusNVD modified after enrichment

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates ↗
  1. Affected versionsThe structured affected or fixed version information changed.
    Before
    Apache Tomcat 10 10.0.0-M10 to 10.0.11; Apache Tomcat 10 10.1.0-M1 to 10.1.0-M5; Apache Tomcat 9 9.0.40 to 9.0.53; Apache Tomcat 8 8.5.60 to 8.5.71 · Fixed: An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
    After
    Apache Tomcat 10 10.0.0-M10 to 10.0.11; Apache Tomcat 10 10.1.0-M1 to 10.1.0-M5; Apache Tomcat 9 9.0.40 to 9.0.53; Apache Tomcat 8 8.5.60 to 8.5.71 · Fixed: Before applying this update, make sure all previously released errata relevant to your system have been applied. For details on how to apply this update, refer to: https://access.redhat.com/articles/11258
    Red Hat Product Security ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Fixed release or patch reference recorded
Fixed release recorded from official guidance
ENISA EUVD · EUVD-2021-2266↗Red Hat Product Security security advisory↗CVE authority or vendor reference↗Patch or update reference↗Patch or update reference↗Patch or update reference↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2021-42340 · cve.blacktree.nl