Client Connector: Race Condition within a Thread
CVE-2026-25687 is a high-severity race condition within a thread vulnerability in Client Connector from Zscaler, with a CVSS 3.1 base score of 8.1 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions 4.6.0.486, 4.7.0.350, 4.8.0.267 as the first without the flaw, so updating Client Connector to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.38% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update Client Connector to 4.6.0.486 or 4.7.0.350 or 4.8.0.267 or 4.9.0.412, whichever matches your release line, or a later version.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Zscaler | Client Connector | 4.6 up to, but not including, 4.6.0.486; 4.7 up to, but not including, 4.7.0.350; 4.8 up to, but not including, 4.8.0.267; 4.9 up to, but not including, 4.9.0.412 | 4.6.0.486, 4.7.0.350, 4.8.0.267, 4.9.0.412 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- HighSuccess depends on conditions outside the attacker's control.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by CNA (zscaler.com).
Official description
A race condition in the ZPA tunnel handler of affected versions of Zscaler Client Connector (ZCC) allows a heap corruption, resulting in a denial of service (client crash) and potentially arbitrary code execution in the context of the ZCC process.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Race Condition within a Thread
If two threads of execution use a resource simultaneously, there exists the possibility that resources may be used while invalid, in turn making the state of execution undefined.
How developers prevent this class of flaw
- Use locking functionality. This is the recommended solution. Implement some form of locking mechanism around code which alters or reads persistent data in a multithreaded environment.
- Create resource-locking validation checks. If no inherent locking mechanisms exist, use flags and signals to enforce your own blocking scheme when resources are being used by other threads of execution.
More Race Condition within a Thread vulnerabilities (CWE-366)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Other vulnerabilities in Client Connector
- 7.5 High severity
- 8.1 High severity
- 9.1 Critical severity
- 8.8 High severity
- 8.4 High severity
- 8.8 High severity
Recent Race Condition within a Thread vulnerabilities
- 7.8 High severity
- 9.8 Critical severity
- 8.7 High severity
- 7.0 High severity
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