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JettyApplication · Eclipse

CVE-2019-17638

CRITICAL · 9.4 CVSS v3.1 Published 2020-07-09
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
100/100
Remediation priority · Urgent
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
In Eclipse Jetty, versions 9.4.27.v20200227 to 9.4.29.v20200521, in case of too large response headers, Jetty throws an exception to produce an HTTP 431 error. When this happens, the ByteBuffer containing the HTTP response headers is released back to the ByteBufferPool twice. Because of this double release, two threads can acquire the same ByteBuffer from the pool and while thread1 is about to use the ByteBuffer to write response1 data, thread2 fills the ByteBuffer with other data. Thread1 then proceeds to write the buffer that now contains different data. This results in client1, which issued request1 seeing data from another request or response which could contain sensitive data belonging to client2 (HTTP session ids, authentication credentials, etc.). If the Jetty version cannot be upgraded, the vulnerability can be significantly reduced by configuring a responseHeaderSize significantly larger than the requestHeaderSize (12KB responseHeaderSize and 8KB requestHeaderSize).

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

A double-release vulnerability in Eclipse Jetty's ByteBufferPool causes HTTP response buffer reuse between threads. When response headers exceed the limit and trigger an HTTP 431 error, the ByteBuffer is released twice to the pool, allowing two threads to acquire the same buffer. This causes response data mixing between clients, leaking sensitive information like session IDs and authentication credentials.

MitigationUpgrade to Jetty 9.4.30 or later; alternatively, configure responseHeaderSize to 12KB and requestHeaderSize to 8KB as a workaround.

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
JettyApplication
Affected:= 9.4.27= 9.4.28= 9.4.29

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
High
Integrity
High
Availability
Low

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

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. Determine Jetty version
    Locate the Jetty version by checking the jetty-version.txt file in the Jetty distribution, or inspect the startup logs for the version string (e.g., 'Jetty=9.4.x')
    Affected if The installed version is exactly 9.4.27, 9.4.28, or 9.4.29
  2. Confirm HTTP server is active
    Verify that the Jetty instance is running as an HTTP server (not purely as a servlet container without network listeners) by checking active network listeners or connector configurations
    Affected if Jetty is actively handling HTTP connections and using the ByteBufferPool for response buffer management
  3. Check header size limits
    Review the server connector configuration for 'responseHeaderSize' and 'requestHeaderSize' settings, or test by sending a request with headers exceeding typical limits (e.g., larger than 8KB)
    Affected if Header size limits are configured large enough that oversized headers can trigger an HTTP 431 (Request Header Fields Too Large) response, which activates the vulnerable code path

You are affected if running Jetty 9.4.27, 9.4.28, or 9.4.29 as an HTTP server where request headers can exceed configured limits and trigger HTTP 431 errors, causing the double-release in ByteBufferPool.

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
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade to Jetty 9.4.30 or later; alternatively, configure responseHeaderSize to 12KB and requestHeaderSize to 8KB as a workaround.

Recommended fix High confidence

Jetty 9.4.30 or later

  1. Upgrade Eclipse Jetty from versions 9.4.27, 9.4.28, or 9.4.29 to version 9.4.30 or later.
  2. Verify the upgrade in your environment by testing HTTP responses with large headers.
  3. Alternatively, if upgrade is not immediately feasible, mitigate by configuring the ServerConnector with responseHeaderSize set to 12KB and requestHeaderSize set to 8KB (or similar ratio where responseHeaderSize > requestHeaderSize).
Caveat Review release notes for 9.4.30 for any compatibility changes; minor version upgrade within 9.4.x typically has low breaking change risk

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

Fix this in Jetty Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,080
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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-2019-17638 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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