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ZookeeperApplication · Apache

CVE-2017-5637

HIGH · 7.5 CVSS v3.0 Published 2017-10-10
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
84/100
Remediation priority · High
High EPSS 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
Two four letter word commands "wchp/wchc" are CPU intensive and could cause spike of CPU utilization on Apache ZooKeeper server if abused, which leads to the server unable to serve legitimate client requests. Apache ZooKeeper thru version 3.4.9 and 3.5.2 suffer from this issue, fixed in 3.4.10, 3.5.3, and later.

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 ZooKeeper versions 3.4.9 and earlier and 3.5.2 and earlier contain a denial-of-service vulnerability where two four-letter word commands (wchp and wchc) trigger excessive CPU consumption when executed, rendering the server unable to serve legitimate client requests.

MitigationUpgrade Apache ZooKeeper to version 3.4.10, 3.5.3, or later. If immediate upgrade is not possible, restrict network access to the ZooKeeper client port (2181) to prevent unauthorized four-letter command execution.

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
ZookeeperApplication
Affected:= 3.4.0= 3.4.1= 3.4.2= 3.4.3= 3.4.4= 3.4.5= 3.4.6= 3.4.7= 3.4.8= 3.4.9= 3.5.0= 3.5.1
Debian LinuxOperating system
Affected:= 8.0

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:3.0/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 ZooKeeper version
    Run 'echo stat | nc <zookeeper_host> 2181' or check the ZooKeeper startup logs for the version number. Alternatively, use 'zookeeper-server-ctl version' if available.
    Affected if The installed version is 3.4.9 or earlier, or 3.5.2 or earlier (specifically 3.4.0 through 3.4.9 or 3.5.0 through 3.5.1). Compare your version to these ranges.
  2. Check if wchp command is accessible
    Send the four-letter command 'wchp' to ZooKeeper: run 'echo wchp | nc <zookeeper_host> 2181' or use 'telnet <zookeeper_host> 2181' and type 'wchp'.
    Affected if The command returns output (a list of watches) without immediate server slowdown, indicating the command is enabled and the vulnerability is present.
  3. Check if wchc command is accessible
    Send the four-letter command 'wchc' to ZooKeeper: run 'echo wchc | nc <zookeeper_host> 2181' or use 'telnet <zookeeper_host> 2181' and type 'wchc'.
    Affected if The command returns output (a list of watches by session) without immediate server slowdown, indicating the command is enabled and the vulnerability is present.
  4. Verify network exposure
    Check if the ZooKeeper client port 2181 is bound to a public or untrusted network interface. Run 'netstat -tlnp | grep 2181' or 'ss -tlnp | grep 2181' to see listening addresses.
    Affected if Port 2181 is listening on 0.0.0.0 or an exposed network interface, meaning unauthenticated attackers can execute the four-letter commands remotely.

You are affected if ZooKeeper version is 3.4.0-3.4.9 or 3.5.0-3.5.1, the wchp/wchc commands are accessible, and port 2181 is exposed to untrusted networks.

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.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade Apache ZooKeeper to version 3.4.10, 3.5.3, or later. If immediate upgrade is not possible, restrict network access to the ZooKeeper client port (2181) to prevent unauthorized four-letter command execution.

Fix this in Zookeeper Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,930
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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-2017-5637 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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