dbcve.org
TomcatWeb server / proxy · Apache

CVE-2021-41079

HIGH · 7.5 CVSS v3.1 Published 2021-09-16
Fix available
A fix is available. Upgrade to 8.5.64 / 9.0.44 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Apache Tomcat versions 8.5.0-8.5.63, 9.0.0-M1-9.0.43, and 10.0.0-M1-10.0.2 fail to validate incoming TLS packets properly. When configured with NIO+OpenSSL or NIO2+OpenSSL connectors, a specially crafted malformed TLS packet triggers an infinite loop in the processing logic, causing a denial of service condition.

MitigationUpgrade to Tomcat 8.5.64+, 9.0.44+, or 10.0.3+ which contain the fix, or reconfigure Tomcat to use alternative TLS connectors (NIO or BIO) if upgrading is not immediately feasible.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
TomcatWeb server / proxy
Affected:>= 8.5.0, < 8.5.64>= 9.0.0, < 9.0.44>= 10.0.0, <= 10.0.2
Debian LinuxOperating system
Affected:= 9.0= 10.0= 11.0
Management Services For Element Software And Netapp HciApplication
Affected:all versions

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify installed Tomcat version
    Run `catalina.sh version` or check the jar file name in the Tomcat lib directory, such as catalina.jar metadata
    Affected if version is 8.5.0-8.5.63, 9.0.0-9.0.43, or 10.0.0-10.0.2
  2. Locate server.xml configuration file
    Find the server.xml file in the Tomcat conf directory (commonly $CATALINA_HOME/conf/server.xml)
    Affected if file exists and contains connector definitions
  3. Check connector protocol implementation
    Search server.xml for connector elements with protocol attribute set to org.apache.coyote.http11.Http11Nio2Protocol or org.apache.coyote.http11.Http11NioProtocol combined with SSLEnabled="true" and configured to use OpenSSL (check for openssl.* or SSLImplementation attributes)
    Affected if connector uses NIO+OpenSSL or NIO2+OpenSSL configuration
  4. Verify OpenSSL usage in connector
    Examine the connector for OpenSSL-specific attributes such as SSLImplementation="org.apache.tomcat.util.net.openssl.OpenSSLImplementation" or similar OpenSSL class references in the connector configuration
    Affected if OpenSSL is explicitly configured as the SSL implementation for the NIO or NIO2 connector

You are affected if your Tomcat version falls within 8.5.0-8.5.63, 9.0.0-9.0.43, or 10.0.0-10.0.2 AND you have a connector configured with NIO+OpenSSL or NIO2+OpenSSL protocols.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 8.5.64 / 9.0.44 or later
Fixed in 8.5.649.0.44
Interim mitigation

Upgrade to Tomcat 8.5.64+, 9.0.44+, or 10.0.3+ which contain the fix, or reconfigure Tomcat to use alternative TLS connectors (NIO or BIO) if upgrading is not immediately feasible.

Recommended fix High confidence

Apache Tomcat 8.5.64+ / 9.0.44+ / 10.0.3+ (choose the branch matching your major version)

  1. Identify the currently running Tomcat version using the version.sh script or by checking the release notes
  2. For Tomcat 8.5.x: Upgrade to version 8.5.64 or later by replacing the Tomcat installation files
  3. For Tomcat 9.0.x: Upgrade to version 9.0.44 or later by replacing the Tomcat installation files
  4. For Tomcat 10.0.x: Upgrade to version 10.0.3 or later by replacing the Tomcat installation files
  5. After upgrading, restart the Tomcat service
  6. Verify the TLS configuration uses NIO+OpenSSL or NIO2+OpenSSL connector and test that normal TLS connections work
Caveat Ensure application compatibility with the new Tomcat version before deploying to production

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Tomcat Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
7.0 hours of engineering $1,240
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,984.

Scan for this in your stack

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-41079 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data