CVE-2017-20201
Published: 08 October 2025
Summary
CVE-2017-20201 is a critical-severity Embedded Malicious Code (CWE-506) vulnerability in Avast (inferred from references). Its CVSS base score is 9.3 (Critical).
Operationally, ranked at the 34.1th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2025-33278
Vulnerability details
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,…
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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.
- CWE(s)
Related Threats
No named actor attribution yet. ATT&CK technique mapping in progress for this CVE.
Affected Assets
Mitigating Controls
Likely Mitigating Controls AI
Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.
Restricting software to licensed versions and controlling P2P prevents introduction of software containing embedded malicious code from unauthorized sources.
The control prevents users from installing software that contains embedded malicious code.
Regular inventory reviews and updates make it harder to conceal or exploit embedded malicious code by requiring all components to be documented and accounted for.
Reverting to a known state removes any malicious code embedded by an attacker.
The approval and review process for maintenance tools can prevent introduction or continued use of tools containing embedded malicious code.
Supply chain strategy requires vetting and controls during acquisition to prevent or detect insertion of malicious code by vendors or integrators.
Background screening for development or deployment roles makes intentional insertion of malicious code by insiders materially harder to accomplish.
The capability explicitly searches for embedded malicious code and backdoors as indicators of compromise.