CVE-2017-20201

CRITICALNVD 9.39.3—
EchelonGraph scoreMEDIUM confidence

This critical-severity CVE scores 9.3 under NVD CVSS v3. EPSS exploit probability: 0.5%, top 61% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
Elevated
9.3
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 0%CVSS: 9.3Exploit: NoneExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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.

CVSS v3
9.3
EG Score
9.3(medium)
EPSS
39.5%
KEV
Not listed

Published

October 8, 2025

Last Modified

April 15, 2026

Advisory Details (8)

Auto-updated Jul 17, 2026
⚠️ Active exploitation confirmed. No patch confirmed yet.
generic

CCleaner Backdoor: Analysis & Recommendations - CrowdStrike

https://www.crowdstrike.com/en-us/blog/protecting-software-supply-chain-deep-insights-ccleaner-backdoor/
generic

CCleaner v5.33.6162 & CCleaner Cloud v1.07.3191 Malicious Backdoor Supply Chain Compromise | Advisories | VulnCheck

https://www.vulncheck.com/advisories/ccleaner-and-ccleaner-cloud-malicious-backdoor-supply-chain-compromise
generic

Morphisec Discovers CCleaner Backdoor Saving Millions of Avast Users

https://www.morphisec.com/blog/morphisec-discovers-ccleaner-backdoor/
generic

Security Notification for CCleaner v5.33.6162 and CCleaner Cloud v1.07.3191 for 32-bit Windows users

https://www.ccleaner.com/knowledge/security-notification-ccleaner-v5336162-ccleaner-cloud-v1073191
generic

CCleaner Makes Your Computer Faster & More Secure | Official Website

https://www.ccleaner.com/
generic🔴 Active Exploitation

CCleanup: A Vast Number of Machines at Risk

https://blog.talosintelligence.com/avast-distributes-malware/
generic

Update to the CCleaner 5.33.6162 Security Incident

https://blog.avast.com/update-to-the-ccleaner-5.33.6162-security-incident
generic

Progress on CCleaner Investigation

https://blog.avast.com/progress-on-ccleaner-investigation

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 13× in last 7d / 40× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-07-22 22:08 UTCEG score recompute
  2. 2026-07-22 14:04 UTCEPSS rescore
  3. 2026-07-22 14:04 UTCEPSS rescore
  4. 2026-07-21 15:21 UTCEPSS rescore
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  1. 2026-07-05 02:27 UTCEPSS rescore
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  32. 2026-06-10 22:15 UTCEPSS rescore
  33. 2026-06-10 13:19 UTCEPSS rescore
  34. 2026-06-08 15:25 UTCEG score recompute▲ 9.30
  35. 2026-06-08 15:25 UTCGHSA enrichment
  36. 2026-06-08 14:14 UTCEPSS rescore
  37. 2026-06-08 14:14 UTCEPSS rescore
  38. 2026-06-07 15:22 UTCEPSS rescore
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  40. 2026-06-06 13:45 UTCEPSS rescore
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  45. 2026-06-04 13:10 UTCEPSS rescore
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  67. 2026-05-21 22:40 UTCEPSS rescore
  68. 2026-05-21 06:45 UTCEG score recompute
  69. 2026-05-21 06:45 UTCGHSA enrichment
  70. 2026-05-20 22:37 UTCEPSS rescore
  71. 2026-05-20 22:37 UTCEPSS rescore
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  73. 2026-05-20 11:21 UTCEPSS rescore
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  75. 2026-05-18 21:30 UTCEPSS rescore

Frequently asked(5)

What is CVE-2017-20201?
CVE-2017-20201 is a critical vulnerability published on October 8, 2025. CCleaner v5.33.6162 and CCleaner Cloud v1.07.3191 (32-bit builds) contained a malicious pre-entry-point loader that diverts execution from scrtcommonmain_seh into a custom loader. That loader decodes an embedded blob into shellcode, allocates executable heap memory, resolves Windows API functions…
When was CVE-2017-20201 disclosed?
CVE-2017-20201 was first published in the National Vulnerability Database on October 8, 2025, with the most recent update on April 15, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2017-20201 actively exploited?
CVE-2017-20201 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 39.5% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2017-20201?
CVE-2017-20201 has a CVSS v3 base score of 9.3 (NVD).
How do I remediate CVE-2017-20201?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2017-20201, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

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