Description
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.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| Apache Software Foundation | Apache ZooKeeper | 3.4.0 to 3.4.9, 3.5.0 to 3.5.2 | — |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | zookeeper | 3.4.9-3 | — |
| Debian 13 | zookeeper | 3.4.9-3 | — |
| Debian 12 | zookeeper | 3.4.9-3 | — |
| Debian 8 | zookeeper | 3.4.5+dfsg-2+deb8u2 | DSA-3871-1 |
| Debian 7 | zookeeper | 3.4.5+dfsg-2+deb7u1 | DLA-986-1 |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu Pro 16.04 LTS | zookeeper | 3.4.8-1ubuntu0.1~esm1 | USN-4789-1 |
| Ubuntu Pro 14.04 LTS | zookeeper | 3.4.5+dfsg-1ubuntu0.1~esm1 | USN-4789-1 |
SUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SUSE OpenStack Cloud Crowbar 8 | crowbar-core | 5.0+git.1585575551.16781d00d-3.38.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud Crowbar 8 | crowbar-ha | 5.0+git.1585316176.344190f-3.32.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud Crowbar 8 | crowbar-openstack | 5.0+git.1585304226.2164b7895-4.37.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud Crowbar 8 | documentation-suse-openstack-cloud-deployment +3 | 8.20200319-1.23.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud Crowbar 8 | memcached | 1.5.17-3.3.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud Crowbar 8 | openstack-manila | 5.1.1~dev5-3.26.2 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud Crowbar 8 | openstack-manila-doc | 5.1.1~dev5-3.26.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud Crowbar 8 | openstack-neutron | 11.0.9~dev63-3.30.2 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud Crowbar 8 | openstack-neutron-doc | 11.0.9~dev63-3.30.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud Crowbar 8 | openstack-nova | 16.1.9~dev61-3.35.2 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud Crowbar 8 | openstack-nova-doc | 16.1.9~dev61-3.35.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud Crowbar 8 | python-amqp | 2.4.2-3.9.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud Crowbar 8 | rubygem-puma | 2.16.0-3.6.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud Crowbar 8 | zookeeper | 3.4.10-3.6.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | ardana-ansible | 8.0+git.1583432621.24fa60e-3.70.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | ardana-barbican | 8.0+git.1585152761.8ef3d61-4.33.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | ardana-db | 8.0+git.1583944923.03cca6c-3.31.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | ardana-monasca | 8.0+git.1583944894.38f023a-3.24.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | ardana-mq | 8.0+git.1583944811.dc14403-3.19.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | ardana-neutron | 8.0+git.1584715262.e4ea620-3.39.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | ardana-octavia | 8.0+git.1585171918.418f5cf-3.26.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | ardana-tempest | 8.0+git.1585311051.6ab5488-3.33.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | documentation-suse-openstack-cloud-user +8 | 8.20200319-1.23.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | memcached | 1.5.17-3.3.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | openstack-manila | 5.1.1~dev5-3.26.2 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | openstack-manila-doc | 5.1.1~dev5-3.26.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | openstack-neutron | 11.0.9~dev63-3.30.2 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | openstack-neutron-doc | 11.0.9~dev63-3.30.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | openstack-nova | 16.1.9~dev61-3.35.2 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | openstack-nova-doc | 16.1.9~dev61-3.35.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | pdns | 4.1.2-3.6.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | python-amqp | 2.4.2-3.9.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | venv-openstack-aodh | 5.1.1~dev7-12.24.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | venv-openstack-barbican | 5.0.2~dev3-12.25.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | venv-openstack-ceilometer | 9.0.8~dev7-12.22.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | venv-openstack-cinder | 11.2.3~dev23-14.25.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | venv-openstack-designate | 5.0.3~dev7-12.23.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | venv-openstack-freezer | 5.0.0.0~xrc2~dev2-10.20.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | venv-openstack-glance | 15.0.3~dev3-12.23.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | venv-openstack-heat | 9.0.8~dev22-12.25.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | venv-openstack-ironic | 9.1.8~dev8-12.25.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | venv-openstack-keystone | 12.0.4~dev5-11.26.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | venv-openstack-magnum | 5.0.2_5.0.2_5.0.2~dev31-11.24.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | venv-openstack-manila | 5.1.1~dev5-12.29.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | venv-openstack-monasca-ceilometer | 1.5.1_1.5.1_1.5.1~dev3-8.20.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | venv-openstack-murano | 4.0.2~dev2-12.20.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | venv-openstack-neutron | 11.0.9~dev63-13.28.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | venv-openstack-nova | 16.1.9~dev61-11.26.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | venv-openstack-octavia | 1.0.6~dev3-12.25.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | venv-openstack-sahara | 7.0.5~dev4-11.24.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | venv-openstack-trove | 8.0.2~dev2-11.24.1 | SUSE-SU-2020:1066-1 |
| SUSE OpenStack Cloud 8 | zookeeper | 3.4.10-3.6.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | ardana-ansible | 8.0+git.1583432621.24fa60e-3.70.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | ardana-barbican | 8.0+git.1585152761.8ef3d61-4.33.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | ardana-db | 8.0+git.1583944923.03cca6c-3.31.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | ardana-monasca | 8.0+git.1583944894.38f023a-3.24.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | ardana-mq | 8.0+git.1583944811.dc14403-3.19.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | ardana-neutron | 8.0+git.1584715262.e4ea620-3.39.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | ardana-octavia | 8.0+git.1585171918.418f5cf-3.26.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | ardana-tempest | 8.0+git.1585311051.6ab5488-3.33.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | documentation-hpe-helion-openstack-user +5 | 8.20200319-1.23.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | memcached | 1.5.17-3.3.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | openstack-manila | 5.1.1~dev5-3.26.2 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | openstack-manila-doc | 5.1.1~dev5-3.26.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | openstack-neutron | 11.0.9~dev63-3.30.2 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | openstack-neutron-doc | 11.0.9~dev63-3.30.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | openstack-nova | 16.1.9~dev61-3.35.2 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | openstack-nova-doc | 16.1.9~dev61-3.35.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | pdns | 4.1.2-3.6.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | python-amqp | 2.4.2-3.9.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | venv-openstack-aodh | 5.1.1~dev7-12.24.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | venv-openstack-barbican | 5.0.2~dev3-12.25.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | venv-openstack-ceilometer | 9.0.8~dev7-12.22.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | venv-openstack-cinder | 11.2.3~dev23-14.25.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | venv-openstack-designate | 5.0.3~dev7-12.23.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | venv-openstack-freezer | 5.0.0.0~xrc2~dev2-10.20.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | venv-openstack-glance | 15.0.3~dev3-12.23.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | venv-openstack-heat | 9.0.8~dev22-12.25.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | venv-openstack-ironic | 9.1.8~dev8-12.25.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | venv-openstack-keystone | 12.0.4~dev5-11.26.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | venv-openstack-magnum | 5.0.2_5.0.2_5.0.2~dev31-11.24.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | venv-openstack-manila | 5.1.1~dev5-12.29.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | venv-openstack-monasca-ceilometer | 1.5.1_1.5.1_1.5.1~dev3-8.20.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | venv-openstack-murano | 4.0.2~dev2-12.20.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | venv-openstack-neutron | 11.0.9~dev63-13.28.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | venv-openstack-nova | 16.1.9~dev61-11.26.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | venv-openstack-octavia | 1.0.6~dev3-12.25.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | venv-openstack-sahara | 7.0.5~dev4-11.24.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | venv-openstack-trove | 8.0.2~dev2-11.24.1 | SUSE-SU-2020:1066-1 |
| SUSE HPE Helion OpenStack 8 | zookeeper | 3.4.10-3.6.1 | SUSE-SU-2020:1066-1 |
Public exploits
Exploit or proof-of-concept code for this vulnerability is publicly available, which lowers the bar for attackers. Treat it as a reason to patch sooner.
Third-party code, not reviewed by us. Public PoCs are sometimes fake or contain malware. Read the code first and run it only in an isolated lab, against systems you are authorised to test.
Exploit-DB 1
- Zookeeper 3.5.2 Client - Denial of Service EDB-42294 · dos · Jul 2, 2017
Sources: PoC-in-GitHub, Metasploit Framework, Exploit-DB — updated daily. Only links are listed; no exploit code is hosted here.
Affected packages
| Ecosystem | Package | Affected | Fixed | Record |
|---|---|---|---|---|
| Maven | org.apache.zookeeper:zookeeper | >= 3.4.0, < 3.4.10 | 3.4.10 | GHSA-7cwj-j333-x7f7 |
| Maven | org.apache.zookeeper:zookeeper | >= 3.5.0, < 3.5.3 | 3.5.3 | GHSA-7cwj-j333-x7f7 |
Advisories 5
- USN-4789-1 zookeeper vulnerabilities Ubuntu Security Notices (USN) · Jun 29, 2026
- DLA-986-1 zookeeper - security update Debian Security (DSA / DLA) · Mar 9, 2026
- DSA-3871-1 zookeeper - security update Debian Security (DSA / DLA) · Mar 9, 2026
- SUSE-SU-2020:1066-1 Security update for ardana-ansible, ardana-barbican, ardana-db, ardana-monasca, ardana-mq, ardana-neutron, ardana-octavia, ardana-tempest, crowbar-core, crowbar-ha, crowbar-openstack, documentation-suse-openstack-cloud, memcached, openstack-manila, openstack-neutron, openstack-nova, pdns, python-amqp, rubygem-puma, zookeeper SUSE / openSUSE Security Updates · Feb 4, 2026
- WID-SEC-2022-0770 IBM DB2: Mehrere Schwachstellen BSI CERT-Bund (WID) · Jan 8, 2026
References
- [dev] 20171009 [SECURITY] CVE-2017-5637: DOS attack on wchp/wchc four letter words (4lw) mailing-list
- 98814 vdb-entry
- RHSA-2017:3355 vendor-advisory
- RHSA-2017:3354 vendor-advisory
- RHSA-2017:2477 vendor-advisory
- DSA-3871 vendor-advisory
- [activemq-issues] 20190820 [jira] [Created] (AMQ-7279) Security Vulnerabilities in Libraries - jackson-databind-2.9.8.jar, tomcat-servlet-api-8.0.53.jar, tomcat-websocket-api-8.0.53.jar, zookeeper-3.4.6.jar, guava-18.0.jar, jetty-all-9.2.26.v20180806 mailing-list
- [nifi-commits] 20191113 svn commit: r1869773 - /nifi/site/trunk/security.html mailing-list
- [nifi-commits] 20200123 svn commit: r1873083 - /nifi/site/trunk/security.html mailing-list
- https://www.oracle.com/security-alerts/cpujul2020.html
- https://issues.apache.org/jira/browse/ZOOKEEPER-2693
- https://www.oracle.com//security-alerts/cpujul2021.html