# CVE-2021-26736: ZApp Installer Privilege Escalation Vulnerabilities

> A local attacker can execute arbitrary code with SYSTEM privileges due to insecure binary loading in the Zscaler Client Connector installer.

- **Severity:** Medium 6.7 (`CVSS:3.1/AV:L/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 23 Oct 2023
- **Updated:** 27 Feb 2025
- **Also known as:** GHSA-cmfg-v75g-8wm3

## What is CVE-2021-26736?

CVE-2021-26736 is a medium-severity vulnerability in Zscaler Client Connector, published on 23 Oct 2023. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

Multiple vulnerabilities in the Zscaler Client Connector Installer and Uninstaller for Windows prior to 3.6 allowed execution of binaries from a low privileged path. A local adversary may be able to execute code with SYSTEM privileges.

Weakness: CWE-22 (Improper Limitation of a Pathname to a Restricted Directory), CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2021-26736?

It affects 1 product.


Products: Zscaler Client Connector.

## How do I fix CVE-2021-26736?

No fix has been published for CVE-2021-26736 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-26736 being exploited?

There is no known exploitation of CVE-2021-26736 in the wild and no public exploit code.

## Other vulnerabilities in Zscaler Client Connector

- [CVE-2020-11633](https://insights.sbomify.com/CVE-2020-11633/): Memory corruption in n/a (critical 9.8)
- [CVE-2024-23463](https://insights.sbomify.com/CVE-2024-23463/): Anti-Tampering bypass via Repair App functionality (high 8.8)
- [CVE-2023-28804](https://insights.sbomify.com/CVE-2023-28804/): Linux ZCC allows unsigned updates, allowing elevated Code Execution (high 8.2)
- [CVE-2023-28799](https://insights.sbomify.com/CVE-2023-28799/): Open redirect in Client Connector (high 8.2)
- [CVE-2023-28800](https://insights.sbomify.com/CVE-2023-28800/): Output encoding missing in redrurl parameter (high 8.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-26736 and fix it if it is affected.

What it is: CVE-2021-26736 is a medium-severity vulnerability in Zscaler Client Connector, published on 23 Oct 2023. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2021-26736 in the wild and no public exploit code.

Affected product: Zscaler Client Connector. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2021-26736/ (Markdown: https://insights.sbomify.com/CVE-2021-26736/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-26736
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-26736
- OSV: https://osv.dev/vulnerability/CVE-2021-26736

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-26736/
Summaries are generated and may contain mistakes; the official description above is the record.