TomcatWeb server / proxy · Apache
CVE-2016-6817
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 · uneditedThe HTTP/2 header parser in Apache Tomcat 9.0.0.M1 to 9.0.0.M11 and 8.5.0 to 8.5.6 entered an infinite loop if a header was received that was larger than the available buffer. This made a denial of service attack possible.
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 confidenceThe HTTP/2 header parser in Apache Tomcat 9.0.0.M1-M11 and 8.5.0-8.5.6 enters an infinite loop when processing a header that exceeds the available buffer size, causing the server to hang and enabling a denial of service attack.
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
= 8.5.0= 8.5.1= 8.5.2= 8.5.3= 8.5.4= 8.5.5= 8.5.6= 9.0.0CVSS 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 checksWork through these to decide whether this CVE applies to you.
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Confirm HTTP/2 protocol support is enabledInspect your server.xml configuration file for an HTTP/2 connector definition. Look for the <UpgradeProtocol> element with className="org.apache.coyote.http2.Http2Protocol" inside a Connector element, or check for protocol="HTTP/1.1" with optional http2Upgrade="true" attribute.Affected if HTTP/2 is enabled via connector configuration - the vulnerability only applies when HTTP/2 protocol handling is active
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Identify the installed Tomcat versionLocate the RELEASE-NOTE file in the Tomcat installation directory, or run the version.sh/version.bat script in the bin folder, or check the catalina.jar manifest file for the Implementation-Version attribute.Affected if The installed version is 8.5.0 through 8.5.6 inclusive, or 9.0.0.M1 through 9.0.0.M11 inclusive
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Compare against affected version rangesReview the version number obtained from the previous step and compare it to the known vulnerable versions: 8.5.0-8.5.6 and 9.0.0.M1-9.0.0.M11.Affected if The version falls within the 8.5.0-8.5.6 range or the 9.0.0.M1-9.0.0.M11 range
A user is affected if they are running Tomcat 8.5.0-8.5.6 or 9.0.0.M1-M11 with HTTP/2 protocol support enabled, as the infinite loop condition in the HTTP/2 header parser requires both a vulnerable version and active HTTP/2 handling.
Generated from the published advisory. Verify against your own configuration.
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.
From vendor dataUpgrade to Apache Tomcat 9.0.0.M12, 8.5.7, or later which contain the fix for this vulnerability.
Fix this in Tomcat
Scoped from the published advisory
- Consultation2.0 h
- Implementation4.0 h
- Testing8.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,288.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2016-6817 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2016-6817 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- 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
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