VulnerabilityPublished 16 Sep 2026Updated 17 Sep 2026

CVE-2026-59969: Apache ZooKeeper · Improper Validation of Certificate with Host Mismatch

Affects Apache ZooKeeperSource CVE Database V5

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Not known to be exploited · CVSS 7.5 High · fixed in 3.8.7 : patch Apache ZooKeeper soon.

Data as of 31 Oct 2026, 08:20 UTC

CVSS 3.1 base score

7.5High

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.3% chance of exploitation in 30 days – higher than 26% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 3.8.7

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: High
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 16 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

ghsa-4pv3-cr63-m4ph

What to do

Affected software

Product	Affected	Fixed in
Apache Software FoundationApache ZooKeeper	Affected >=3.9.0 <=3.9.5 >=3.8.0 <=3.8.6	Fixed in–
MavenApache Software Foundation/org.apache.zookeeper:zookeeper`pkg:maven/Apache Software Foundation/org.apache.zookeeper:zookeeper`Other threats	Affected >=3.9.0 <=3.9.5 >=3.8.0 <=3.8.6	Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Users should upgrade Apache ZooKeeper to version 3.8.7 or 3.9.6, where this vulnerability is fixed. No other mitigation or temporary workaround is indicated in the available data.

Description

Apache ZooKeeper versions 3.8.0 through 3.8.6 and 3.9.0 through 3.9.5 have a vulnerability in quorum TLS where peer hostname verification is improperly enforced in FIPS-mode deployments. This allows a CA-trusted peer certificate with a Subject Alternative Name (SAN) that does not match the connected host to join quorum traffic, participate in leader election, and enter replication flows. The issue is fixed in versions 3.8.7 and 3.9.6.

Impact

An attacker with a malicious or misissued CA-trusted certificate can impersonate a quorum peer in Apache ZooKeeper, potentially influencing leader election and replication processes. This could lead to unauthorized participation in critical cluster operations, impacting the integrity of the ZooKeeper quorum. The CVSS score of 7.5 (high) reflects the significant impact on integrity without affecting confidentiality or availability.

CWE-297Improper Validation of Certificate with Host Mismatch (opens in a new tab)
Variant weaknessLikelihood of exploit: HighOWASP Top 10 A07:2025: Authentication Failures (opens in a new tab)
The product communicates with a host that provides a certificate, but the product does not properly ensure that the certificate is actually associated with that host.
Architecture and Design
In order to ensure data integrity, the certificate must be valid, and it must pertain to the site that is being accessed.Fully check the hostname of the certificate and provide the user with adequate information about the nature of the problem and how to proceed.
Implementation
If certificate pinning is being used, ensure that all relevant properties of the certificate are fully validated before the certificate is pinned, including the hostname.
Implementation
Be careful of other weaknesses in the code that checks the hostname, since it is still possible to incorrectly check the hostname. For example, attackers could create a certificate with a name that begins with a trusted name followed by a NUL byte, which could cause some string-based comparisons to only examine the…
OWASP Cheat Sheets
OWASP Authentication (opens in a new tab)
OWASP ASVS 4.0.3
V1.14.1 (opens in a new tab)
V2.8.5 (opens in a new tab)
V2.8.4 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 18 Oct 2026, 00:28 UTC

WeaknessesCWE-297

Technical details

References

Community reviews

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