# CVE-2017-20201: CCleaner v5.33.6162 & CCleaner Cloud v1.07.3191 Malicious Backdoor Supply Chain Compromise

> Attackers can execute malicious code and exfiltrate data via a backdoor in compromised CCleaner installers, requiring users to upgrade to clean versions.

- **Severity:** Critical 9.3 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:N/SC:H/SI:H/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 8 Oct 2025
- **Updated:** 21 Nov 2025
- **Also known as:** GHSA-mqc2-pwjw-2w78

## What is CVE-2017-20201?

CVE-2017-20201 is a critical vulnerability in Piriform CCleaner, published on 8 Oct 2025. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

CCleaner v5.33.6162 and CCleaner Cloud v1.07.3191 (32-bit builds) contained a malicious pre-entry-point loader that diverts execution from __scrt_common_main_seh into a custom loader. That loader decodes an embedded blob into shellcode, allocates executable heap memory, resolves Windows API functions at runtime, and transfers execution to an in-memory payload. The payload performs anti-analysis checks, gathers host telemetry, encodes the data with a two-stage obfuscation, and attempts HTTPS exfiltration to hard-coded C2 servers or month-based DGA domains. Potential impacts include remote data collection and exfiltration, stealthy in-memory execution and persistence, and potential lateral movement. CCleaner was developed by Piriform, which was acquired by Avast in July 2017; Avast later merged with NortonLifeLock to form the parent company now known as Gen Digital. According to vendor advisories, the compromised CCleaner build was released on August 15, 2017 and remediated on September 12, 2017 with v5.34; the compromised CCleaner Cloud build was released on August 24, 2017 and remediated on September 15, 2017 with v1.07.3214.

Weakness: CWE-506 (Embedded Malicious Code)

## Which versions are affected by CVE-2017-20201?


## How do I fix CVE-2017-20201?

No fix has been published for CVE-2017-20201 yet. Limit exposure of the affected software until one is available.

## Is CVE-2017-20201 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2017-20201 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2017-20201 and fix it if it is affected.

What it is: CVE-2017-20201 is a critical vulnerability in Piriform CCleaner, published on 8 Oct 2025. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2017-20201 exists.

Affected product: Piriform CCleaner. 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-2017-20201/ (Markdown: https://insights.sbomify.com/CVE-2017-20201/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2017-20201
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2017-20201
- OSV: https://osv.dev/vulnerability/CVE-2017-20201

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From sbomify Insights: https://insights.sbomify.com/CVE-2017-20201/
Summaries are generated and may contain mistakes; the official description above is the record.