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Full vulnerability report · 2021
CVE-2021-41079High confidence

Apache Tomcat DoS with unexpected TLS packet

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:High, unchanged from published severity.unchanged

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 7.18% 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 30 daysRemediation target: Within 180 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.9.0.53-1Debian Security Tracker ↗Source updated 6 Oct 2026
Debian bookwormbookworm · sourcetomcat9Vendor fix publishedDebian records a fixed source-package version for this release.9.0.53-1Debian Security Tracker ↗Source updated 6 Oct 2026
Debian forkyforky · sourcetomcat9Vendor fix publishedDebian records a fixed source-package version for this release.9.0.53-1Debian Security Tracker ↗Source updated 6 Oct 2026
Debian sidsid · sourcetomcat9Vendor fix publishedDebian records a fixed source-package version for this release.9.0.53-1Debian Security Tracker ↗Source updated 6 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-2021-41079 · CSAF 2.0 · revision 3 · finalRed Hat Product Securitytomcat: Infinite loop while reading an unexpected TLS packet when using OpenSSL JSSE engine
8 known affected

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

  • pki-servlet-4.0-api (pki-deps:10.6) as a component of Red Hat Enterprise Linux 8
  • pki-servlet-engine.src (pki-deps:10.6) as a component of Red Hat Enterprise Linux 8
  • pki-servlet-engine (pki-deps:10.6) as a component of Red Hat Enterprise Linux 8
  • pki-servlet-4.0-api as a component of Red Hat Enterprise Linux 9
  • pki-servlet-engine as a component of Red Hat Enterprise Linux 9
  • pki-servlet-engine.src as a component of Red Hat Enterprise Linux 9
  • tomcat as a component of Red Hat JBoss Fuse 6
  • opendaylight.src as a component of Red Hat OpenStack Platform 10 (Newton)
Summary
A flaw was found in Apache Tomcat. When Tomcat was configured to use NIO+OpenSSL or NIO2+OpenSSL for TLS, a specially crafted packet can trigger an infinite loop, resulting in 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-2021-1985

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

Apache Tomcat 8.5.0 to 8.5.63, 9.0.0-M1 to 9.0.43 and 10.0.0-M1 to 10.0.2 did not properly validate incoming TLS packets. When Tomcat was configured to use NIO+OpenSSL or NIO2+OpenSSL for TLS, a specially crafted packet could be used to trigger an infinite loop resulting in a denial of service.

What

Apache Tomcat 8.5.0 to 8.5.63, 9.0.0-M1 to 9.0.43 and 10.0.0-M1 to 10.0.2 did not properly validate incoming TLS packets. When Tomcat was configured to use NIO+OpenSSL or NIO2+OpenSSL for TLS, a specially crafted packet could be used to trigger an infinite loop resulting in a denial of service.

Why

The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.

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

Apache Tomcat 8.5.0 to 8.5.63, 9.0.0-M1 to 9.0.43 and 10.0.0-M1 to 10.0.2 did not properly validate incoming TLS packets. When Tomcat was configured to use NIO+OpenSSL or NIO2+OpenSSL for TLS, a specially crafted packet could be used to trigger an infinite loop resulting in a denial of service.

Why

The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.

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 → Improper Input Validation → 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-20 ↗

CWE-20: Improper Input Validation. The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.

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-20
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-2022-0607Red 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-2024-0673Apache 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-20210922Security Bulletin 22 Sep 2021

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 22 Sep 2021, published on 22 September 2021. Open the linked bulletin for the product, severity and reference information published in that issue.

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

une exécution de code arbitraire et une atteinte à la confidentialité des données. 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=

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-002489Apache Tomcat におけるサービス運用妨害（DoS）の脆弱性

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-2021-41079 TLS に NIO と OpenSSL または NIO2 と OpenSSL を使用したシステム構成の場合、細工されたパケットを受信すると、TLS の内部処理において無限ループが引き起こされる可能性があります。

Official advisory ↗
NCSC-NL · Dutch · NCSC-2025-0123Kwetsbaarheden verholpen in Oracle Database Producten

De kwetsbaarheden stellen ongeauthenticeerde kwaadwillenden in staat om een Denial-of-Service te veroorzaken of om ongeautoriseerde toegang te verkrijgen tot gevoelige gegevens en gegevens te manipuleren. Subcomponenten als de RDBMS Listener, Java VM, en andere componenten zijn specifiek kwetsbaar, met CVSS-scores variërend van 5.3 tot 7.5, wat duidt op een gematigd tot hoog risico.

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 16 Sept 2021 · Last source change 4 Aug 2024, 02:59 UTC · CWE-20 · Improper Input Validation

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-2021-1985
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 8.5 8.5.0 to 8.5.63; Apache Tomcat 9 9.0.0-M1 to 9.0.43; Apache Tomcat 10 10.0.0-M1 to 10.0.2 · Fixed: No fixed version is explicitly recorded in the structured CVE data.
    After
    Apache Tomcat 8.5 8.5.0 to 8.5.63; Apache Tomcat 9 9.0.0-M1 to 9.0.43; Apache Tomcat 10 10.0.0-M1 to 10.0.2 · 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 ↗
  2. Remediation statusRemediation status changed from Awaiting fix to Patch available.
    Before
    Awaiting fix
    After
    Patch available
    Red Hat Product Security ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Fixed release recorded from official guidance
ENISA EUVD · EUVD-2021-1985↗Red Hat Product Security security advisory↗CVE authority or vendor 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-2021-41079 · cve.blacktree.nl