CVE-2026-100235Apache ZooKeeper time-of-check to time-of-use race
CVE-2026-100235 is a time-of-check to time-of-use race in Apache ZooKeeper, rated medium (6.0 on CVSS 4.0).
Why this priority: Medium severity, with no exploitation signal.
Published · Updated · NVD status: Awaiting Analysis
What it is
Something is checked, then changed by an attacker before it is used.
How it is reached
An attacker can exploit it over the network, with an ordinary user account, and nobody has to click anything. Success also depends on conditions the attacker does not fully control.
What an attacker gains
A successful attack can change data or behaviour. In practice, this kind of flaw lets an attacker win a timing window to bypass a check or corrupt shared state.
Is it being exploited?
There is no public report of exploitation yet. EPSS estimates a 0.34% chance of exploitation activity in the next 30 days, higher than 27% of scored CVEs.
What to do
- No fixed version is listed yet. Find every place Apache ZooKeeper runs, watch the references for a fix, and plan a replacement if it is no longer supported.
- While there is no fix, review who holds accounts that can reach it.
Description from NVD
Incorrect authorization due to a time-of-check to time-of-use (TOCTOU) race condition in the setACL request handling of Apache ZooKeeper.
When a node's ACL is changed via setACL, the pending change is not published to the server's outstanding change record for that node. Any request that is prepared (and authorized) after the setACL is submitted but before it commits is therefore checked against the previous, pre-revocation ACL, yet is applied to the data tree after the ACL change has taken effect. A client that currently holds a permission can use this window to perform operations requiring that permission through and after its revocation — for example, committing writes or deletes after losing write access, or re-granting itself full permissions, which persistently defeats the revocation. In deployments transitioning from the default OPEN_ACL_UNSAFE ACL to a restrictive ACL, any unauthenticated client can exploit this during the transition.
This issue affects Apache ZooKeeper up to and including 3.9.6. Users are recommended to upgrade to version 3.8.8 or 3.9.7, which fixes the issue.
What this means for your architecture.
A CVE names a product. Whether it matters depends on where that product sits in your systems: what reaches it, which trust boundary it guards and what it can reach once compromised. Veriom maps your components, their relationships and your trust boundaries from your code, cloud and delivery evidence, so you can see where a component like this sits. The radar itself does not look at your systems.
Components it touches
- Request handlers and jobs that share state. The flaw sits between concurrent requests or processes.
Trust boundaries in play
- Authenticated network access. An account is needed, so exposure follows who can sign in: customers, partners or staff.
- Between concurrent requests or processes. An attacker who crosses it can win a timing window to bypass a check or corrupt shared state.
Questions to answer about your own systems
- Where does Apache ZooKeeper run in your systems, and at which version?
- Which of those instances can be reached from the internet or partner networks?
- What can it reach once compromised: which data stores, secrets and services?
Sources
- CVE records and CVSS scores from the NVD CVE API. This product uses the NVD API but is not endorsed or certified by the NVD.
- Exploitation status from CISA’s Known Exploited Vulnerabilities catalog.
- Exploit likelihood from FIRST’s Exploit Prediction Scoring System (EPSS), refreshed daily.
- Explanations are written by Veriom from fixed templates over each record’s data, not by a person reviewing each CVE. Descriptions are quoted from the records as published.