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CVE-2026-59969

Apache ZooKeeper: Improper validation of certificate with host mismatch in FIPS mode

7.5 HighFix available

Apache ZooKeeper quorum TLS fails to enforce peer hostname verification in FIPS-mode deployments. When sslQuorum=true, zookeeper.fips-mode=true, ssl.quorum.hostnameVerification=true, and ssl.quorum.clientHostnameVerification=true are enabled, the Java SSLSocket quorum path accepts a CA-trusted peer certificate whose SAN does not match the connected host. A malicious or misissued peer certificate can therefore join quorum traffic, participate in leader election, and enter replication flows.

Users are recommended to upgrade to version 3.8.7 or 3.9.6, which fixes the issue.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
None
Integrity
High
Availability
None

Exploit likelihood

0.33%Up 0.2 points since Sep 16, 2026
90%50%10%1%

What each source reports

CVE List Score used 7.5

Apache ZooKeeper: Improper validation of certificate with host mismatch in FIPS mode

Apache ZooKeeper quorum TLS fails to enforce peer hostname verification in FIPS-mode deployments. When sslQuorum=true, zookeeper.fips-mode=true, ssl.quorum.hostnameVerification=true, and ssl.quorum.clientHostnameVerification=true are enabled, the Java SSLSocket quorum path accepts a CA-trusted peer certificate whose SAN does not match the connected host. A malicious or misissued peer certificate can therefore join quorum traffic, participate in leader election, and enter replication flows.

Users are recommended to upgrade to version 3.8.7 or 3.9.6, which fixes the issue.

Record
CVE-2026-59969
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Weakness
CWE-297
Updated
2026-11-02
EUVDEUVD-2026-80331 7.5

Apache ZooKeeper quorum TLS fails to enforce peer hostname verification in FIPS-mode deployments. When sslQuorum=true, zookeeper.fips-mode=true, ssl.quorum.hostnameVerification=true, and ssl.quorum.clientHostnameVerification=true are enabled, the Java SSLSocket quorum path accepts a CA-trusted peer certificate whose SAN does not match the connected host. A malicious or misissued peer certificate can therefore join quorum traffic, participate in leader election, and enter replication flows.

Users are recommended to upgrade to version 3.8.7 or 3.9.6, which fixes the issue.

Record
EUVD-2026-80331
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Updated
2026-11-02
GitHub AdvisoriesGHSA-4pv3-cr63-m4ph 7.5

Apache ZooKeeper quorum TLS fails to enforce peer hostname verification in FIPS-mode deployments....

Apache ZooKeeper quorum TLS fails to enforce peer hostname verification in FIPS-mode deployments. When sslQuorum=true, zookeeper.fips-mode=true, ssl.quorum.hostnameVerification=true, and ssl.quorum.clientHostnameVerification=true are enabled, the Java SSLSocket quorum path accepts a CA-trusted peer certificate whose SAN does not match the connected host. A malicious or misissued peer certificate can therefore join quorum traffic, participate in leader election, and enter replication flows.

Users are recommended to upgrade to version 3.8.7 or 3.9.6, which fixes the issue.

Record
GHSA-4pv3-cr63-m4ph
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Weakness
CWE-297
Updated
2026-11-02
NVD 7.5

Apache ZooKeeper quorum TLS fails to enforce peer hostname verification in FIPS-mode deployments. When sslQuorum=true, zookeeper.fips-mode=true, ssl.quorum.hostnameVerification=true, and ssl.quorum.clientHostnameVerification=true are enabled, the Java SSLSocket quorum path accepts a CA-trusted peer certificate whose SAN does not match the connected host. A malicious or misissued peer certificate can therefore join quorum traffic, participate in leader election, and enter replication flows.

Users are recommended to upgrade to version 3.8.7 or 3.9.6, which fixes the issue.

Record
CVE-2026-59969
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Weakness
CWE-297
Updated
2026-11-02
OSV 7.5

Apache ZooKeeper: Improper validation of certificate with host mismatch in FIPS mode

Apache ZooKeeper quorum TLS fails to enforce peer hostname verification in FIPS-mode deployments. When sslQuorum=true, zookeeper.fips-mode=true, ssl.quorum.hostnameVerification=true, and ssl.quorum.clientHostnameVerification=true are enabled, the Java SSLSocket quorum path accepts a CA-trusted peer certificate whose SAN does not match the connected host. A malicious or misissued peer certificate can therefore join quorum traffic, participate in leader election, and enter replication flows.

Users are recommended to upgrade to version 3.8.7 or 3.9.6, which fixes the issue.

Record
CVE-2026-59969
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Weakness
CWE-297
Updated
2026-11-02
OSVDEBIAN-CVE-2026-59969 7.5

Apache ZooKeeper quorum TLS fails to enforce peer hostname verification in FIPS-mode deployments. When sslQuorum=true, zookeeper.fips-mode=true, ssl.quorum.hostnameVerification=true, and ssl.quorum.clientHostnameVerification=true are enabled, the Java SSLSocket quorum path accepts a CA-trusted peer certificate whose SAN does not match the connected host. A malicious or misissued peer certificate can therefore join quorum traffic, participate in leader election, and enter replication flows. Users are recommended to upgrade to version 3.8.7 or 3.9.6, which fixes the issue.

Record
DEBIAN-CVE-2026-59969
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Updated
2026-11-02
OSVUBUNTU-CVE-2026-59969 7.5

Apache ZooKeeper quorum TLS fails to enforce peer hostname verification in FIPS-mode deployments. When sslQuorum=true, zookeeper.fips-mode=true, ssl.quorum.hostnameVerification=true, and ssl.quorum.clientHostnameVerification=true are enabled, the Java SSLSocket quorum path accepts a CA-trusted peer certificate whose SAN does not match the connected host. A malicious or misissued peer certificate can therefore join quorum traffic, participate in leader election, and enter replication flows. Users are recommended to upgrade to version 3.8.7 or 3.9.6, which fixes the issue.

Record
UBUNTU-CVE-2026-59969
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Updated
2026-11-02
OSVBIT-zookeeper-2026-59969 No score

Apache ZooKeeper: Improper validation of certificate with host mismatch in FIPS mode

Apache ZooKeeper quorum TLS fails to enforce peer hostname verification in FIPS-mode deployments. When sslQuorum=true, zookeeper.fips-mode=true, ssl.quorum.hostnameVerification=true, and ssl.quorum.clientHostnameVerification=true are enabled, the Java SSLSocket quorum path accepts a CA-trusted peer certificate whose SAN does not match the connected host. A malicious or misissued peer certificate can therefore join quorum traffic, participate in leader election, and enter replication flows.

Users are recommended to upgrade to version 3.8.7 or 3.9.6, which fixes the issue.

Record
BIT-zookeeper-2026-59969
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
zookeeper
Bitnami
 3.8.0 up to 3.8.7, 3.9.0 up to 3.9.6
3.8.73.9.6
zookeeper
Debian:12
 All versions, plus listed versions
3.8.0-113.8.0-11+deb12u13.8.0-11+deb12u23.9.1-13.9.2-1
Show 8 moreShow less
3.9.2-23.9.3-13.9.3-23.9.4-13.9.4-23.9.5-13.9.5-23.9.6-1
 None known
zookeeper
Debian:13
 All versions, plus listed versions
3.9.3-13.9.3-1+deb13u13.9.3-23.9.4-13.9.4-23.9.5-13.9.5-23.9.6-1
 None known
zookeeper
Debian:14
 before 3.9.6-1, plus listed versions
3.9.3-13.9.3-23.9.4-13.9.4-23.9.5-13.9.5-2
3.9.6-1
zookeeper
Ubuntu:Pro:14.04:LTS
 All versions, plus listed versions
3.4.5+dfsg-13.4.5+dfsg-1ubuntu0.1~esm13.4.5+dfsg-1ubuntu0.1~esm3
 None known
zookeeper
Ubuntu:Pro:16.04:LTS
 All versions, plus listed versions
3.4.6-83.4.7-13.4.8-13.4.8-1ubuntu0.1~esm13.4.8-1ubuntu0.1~esm2
 None known
zookeeper
Ubuntu:Pro:18.04:LTS
 All versions, plus listed versions
3.4.10-23.4.10-33.4.13-33.4.13-3ubuntu0.1~esm1
 None known
zookeeper
Ubuntu:20.04:LTS
 All versions, plus listed versions
3.4.13-13.4.13-33.4.13-3build13.4.13-43.4.13-53.4.13-5build13.4.13-5ubuntu0.1
 None known
zookeeper
Ubuntu:22.04:LTS
 All versions, plus listed versions
3.4.13-5ubuntu43.4.13-6ubuntu23.4.13-6ubuntu33.4.13-6ubuntu43.4.13-6ubuntu4.1
 None known
zookeeper
Ubuntu:24.04:LTS
 All versions, plus listed versions
3.8.0-113.9.1-13.9.1-1build13.9.1-1build2
 None known
zookeeper
Ubuntu:26.10
 All versions, plus listed versions
3.9.5-13.9.5-2
 None known
zookeeper
Ubuntu:26.04:LTS
 All versions, plus listed versions
3.9.3-1build23.9.3-1build33.9.4-13.9.5-1
 None known

History

History
RecordedChangedSources
first indexedCVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-59969 is a high vulnerability (CVSS 7.5) in Apache Zookeeper, published September 16, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.33%, the 26th percentile. Fixed in zookeeper 3.8.7.

References

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