CVE-2026-100235
Description
A flaw was found in Apache ZooKeeper. A time-of-check to time-of-use (TOCTOU) race condition during Access Control List (ACL) updates allows operations to be evaluated against outdated permissions. An attacker can exploit the timing window between an ACL update submission and its final commit to execute unauthorized actions, such as modifying data or re-granting full permissions after access has been revoked.
Statement
This vulnerability is rated as Moderate impact because exploiting it requires winning a precise time-of-check to time-of-use timing window specifically during active access control modifications. In standard Red Hat deployments, ZooKeeper is utilized as an internal cluster coordination service isolated from public network access, meaning an attacker must already possess network access and existing permissions on the target node prior to revocation. While an adversary could retain revoked rights or apply unauthorized changes if a request is processed in this brief window, normal operations outside of explicit permission reconfiguration remain unaffected.
Mitigation
Restrict network exposure by limiting access to ZooKeeper client listener ports (default 2181/TCP) to trusted cluster hosts only, and perform access control modifications during scheduled maintenance windows when client workloads are stopped.
To restrict access to ZooKeeper client ports using firewalld:
firewall-cmd --permanent --zone=public --remove-port=2181/tcp
firewall-cmd --permanent --zone=trusted --add-source=<trusted_ip_or_subnet>
firewall-cmd --reload
Warning: Modifying firewall rules and reloading firewalld disrupts existing network connections and may temporarily disconnect active cluster sessions. Ensure all authorized endpoints are configured before reloading.
Caveats: Restricting network reachability prevents untrusted external clients from exploiting the race condition during transitions from open access control lists. However, it does not prevent already-authorized clients on trusted subnets from exploiting the timing window during permission revocation unless concurrent client traffic is paused.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 5.3 | N/A | N/A |
| Attack Vector | Network | N/A | N/A |
| Attack Complexity | High | N/A | N/A |
| Privileges Required | Low | N/A | N/A |
| User Interaction | None | N/A | N/A |
| Scope | Unchanged | N/A | N/A |
| Confidentiality | None | N/A | N/A |
| Integrity Impact | High | N/A | N/A |
| Availability Impact | None | N/A | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N
Understanding the Weakness (CWE)
Integrity,Other
Technical Impact: Alter Execution Logic; Unexpected State
The attacker can gain access to otherwise unauthorized resources.
Integrity,Other
Technical Impact: Modify Application Data; Modify Files or Directories; Modify Memory; Other
Race conditions such as this kind may be employed to gain read or write access to resources which are not normally readable or writable by the user in question.
Integrity,Other
Technical Impact: Other
The resource in question, or other resources (through the corrupted one), may be changed in undesirable ways by a malicious user.
Non-Repudiation
Technical Impact: Hide Activities
If a file or other resource is written in this method, as opposed to in a valid way, logging of the activity may not occur.
Non-Repudiation,Other
Technical Impact: Other
In some cases it may be possible to delete files a malicious user might not otherwise have access to, such as log files.
Other
Technical Impact: Unexpected State
The product may perform invalid actions when the resource is in an unexpected state.
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