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.
CVE-2017-20201
“—” beside the score: it is equal to NVD's CVSS score.
This critical-severity CVE scores 9.3 under NVD CVSS v3. EPSS exploit probability: 0.5% (44th percentile of EPSS-scored CVEs). No GitHub Security Advisory CVSS is on record for this CVE.
Also known asEUVD-2025-33278 (ENISA EUVD) · GHSA-mqc2-pwjw-2w78 (GitHub Security Advisories)Source: ENISA EUVD
- CISA's Vulnrichment rates exploitation as PoC; EchelonGraph holds no exploit-code reference for it
A fix is referenced (a reference tagged "Patch", often a source commit), but no release containing it is confirmed — find the release that contains it; until it is applied, mitigate (WAF / firewall / segmentation).
- CVSS v3
- 9.3
- EG Score
- 9.3CRITICALmedium confidence
- EG Risk
- 58EG Risk 58/100
EG Risk is EchelonGraph's 0–100 priority score. It fuses impact severity (EG Severity, the CVSS base score, never the KEV-floored or EPSS-lifted EG Score) with real-world exploitation and automatability, under weights EchelonGraph set by hand, so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner.
How it’s computed (value × EchelonGraph’s weight)Severity93% × 45%Impact severity (EG Severity): CVSS 9.3 of 10. Never the KEV-floored or EPSS-lifted EG Score.Exploitation40% × 40%EchelonGraph's fixed weight for EG-KEV Tier 3 (Elevated): a constant, not a probability.Automatability0% × 15%CISA's SSVC Automatable value: no (Vulnrichment).SSVC (CISA's decision table, applied by EchelonGraph): Track at low, Track* at medium and Attend at high mission impact.Exploitation public PoC (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.Action: A fix is referenced, but no release containing it is confirmed. Check the referenced fix and the vendor's advisory for a release that contains it; until one is applied, restrict network exposure of the affected system or apply the vendor's mitigation on your normal schedule at low or medium mission impact and sooner than that at high. - EPSS PROB
- 0.5%
- EPSS %ILE
- 44th
- KEV
- Not listed
What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)
The EG score (9.3): severity, escalated by confirmed exploitation. This CVE's 9.3 is its impact severity (EG Severity), not escalated.
- EG Severity
- 9.3 CRITICALCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.NVD CVSS v3 · CVSS v3.0 or v3.1
- EG Likelihood
- 0.5% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-11-01). FIRST's exploitation probability, not an EchelonGraph model.
- Confirmed exploitation
- None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
- EG Priority
- SSVC Track* at medium mission impactTrack at low, Track* at medium and Attend at high mission impact.CISA BOD 26-04: 14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.No released fix is confirmed on this page, but CISA's timeline does not wait for a fix's release: it starts when an agency identifies the flaw on an asset and updates the CDM Agency and Federal Dashboard, and the directive counts patching, decommissioning the system or another action as remediation. Until a fixed release is applied, mitigate as this page's verdict says. In the directive's words, “Fix on system upgrade” means that, “unless conditions change”, the vulnerability “should be remediated the next time the vulnerable asset receives a scheduled major upgrade or rebuild”: its timelines are “dynamic as facts change”, and a KEV listing shortens them.Each input and its source, and whom BOD 26-04 binds: the SSVC and BOD 26-04 blocks below.
SSVC (CISA's decision table, applied by EchelonGraph)Track at low, Track* at medium and Attend at high mission impact.
A fix is referenced, but no release containing it is confirmed. Check the referenced fix and the vendor's advisory for a release that contains it; until one is applied, restrict network exposure of the affected system or apply the vendor's mitigation on your normal schedule at low or medium mission impact and sooner than that at high.
Exploitation public PoC (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table
BOD 26-04 (CISA's remediation timeline, Table 1)14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.
No released fix is confirmed on this page, but CISA's timeline does not wait for a fix's release: it starts when an agency identifies the flaw on an asset and updates the CDM Agency and Federal Dashboard, and the directive counts patching, decommissioning the system or another action as remediation. Until a fixed release is applied, mitigate as this page's verdict says. In the directive's words, “Fix on system upgrade” means that, “unless conditions change”, the vulnerability “should be remediated the next time the vulnerable asset receives a scheduled major upgrade or rebuild”: its timelines are “dynamic as facts change”, and a KEV listing shortens them.
The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it
Published
October 8, 2025
Last Modified
April 15, 2026
Advisory Details (8)
Auto-updated Sep 15, 2026CCleaner Backdoor: Analysis & Recommendations - CrowdStrike
https://www.crowdstrike.com/en-us/blog/protecting-software-supply-chain-deep-insights-ccleaner-backdoor/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-compromiseMorphisec Discovers CCleaner Backdoor Saving Millions of Avast Users
https://www.morphisec.com/blog/morphisec-discovers-ccleaner-backdoor/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-v1073191CCleaner Makes Your Computer Faster & More Secure | Official Website
https://www.ccleaner.com/CCleanup: A Vast Number of Machines at Risk
https://blog.talosintelligence.com/avast-distributes-malware/Update to the CCleaner 5.33.6162 Security Incident
https://blog.avast.com/update-to-the-ccleaner-5.33.6162-security-incidentWeakness Classification(1)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 21× in last 7d / 71× in last 30d)
Each row is a time one of our pipelines fetched, updated or re-scored this CVE. 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. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.
Showing the most recent 97 of 216 refreshes on record for this CVE.
A repeat, a row identical to one the same pipeline wrote less than 10 seconds earlier, is not a separate refresh and is not counted. 3 repeat rows among the latest 100 are merged into the row they repeat. The 119 oldest rows on record are not shown and were not checked, so the counts can still include repeats.
- 2026-11-02 16:34 UTCEPSS rescoreEPSS 0.5% · 44th percentile
- 2026-11-02 09:21 UTCEG score recompute
- 2026-11-02 09:21 UTCGHSA enrichmentGHSA-mqc2-pwjw-2w78 · GitHub severity CRITICAL
- 2026-11-01 16:28 UTCEPSS rescoreEPSS 0.5% · 44th percentile
- 2026-11-01 08:21 UTCEG score recompute
- 2026-11-01 08:21 UTCGHSA enrichmentGHSA-mqc2-pwjw-2w78 · GitHub severity CRITICAL
- 2026-10-31 16:27 UTCEPSS rescoreEPSS 0.5% · 44th percentile
- 2026-10-31 07:23 UTCEG score recompute
- 2026-10-31 07:23 UTCGHSA enrichmentGHSA-mqc2-pwjw-2w78 · GitHub severity CRITICAL
- 2026-10-30 16:27 UTCEPSS rescoreEPSS 0.5% · 44th percentile
- 2026-10-30 06:24 UTCEG score recompute
- 2026-10-30 06:24 UTCGHSA enrichmentGHSA-mqc2-pwjw-2w78 · GitHub severity CRITICAL
- 2026-10-29 16:27 UTCEPSS rescoreEPSS 0.5% · 44th percentile
- 2026-10-29 05:26 UTCEG score recompute
- 2026-10-29 05:25 UTCGHSA enrichmentGHSA-mqc2-pwjw-2w78 · GitHub severity CRITICAL
- 2026-10-28 16:27 UTCEPSS rescoreEPSS 0.5% · 44th percentile
- 2026-10-28 04:26 UTCEG score recompute
- 2026-10-28 04:26 UTCGHSA enrichmentGHSA-mqc2-pwjw-2w78 · GitHub severity CRITICAL
- 2026-10-27 16:26 UTCEPSS rescoreEPSS 0.5% · 44th percentile
- 2026-10-27 03:22 UTCEG score recompute
- 2026-10-27 03:22 UTCGHSA enrichmentGHSA-mqc2-pwjw-2w78 · GitHub severity CRITICAL
- 2026-10-26 16:26 UTCEPSS rescoreEPSS 0.5% · 44th percentile
- 2026-10-25 22:18 UTCGHSA enrichmentGHSA-mqc2-pwjw-2w78 · GitHub severity CRITICAL
- 2026-10-25 19:35 UTCEG score recompute
- 2026-10-25 16:27 UTCEPSS rescoreEPSS 0.5% · 44th percentile
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- 2026-10-24 21:13 UTCEG score recompute
- 2026-10-24 21:12 UTCGHSA enrichmentGHSA-mqc2-pwjw-2w78 · GitHub severity CRITICAL
- 2026-10-24 16:27 UTCEPSS rescoreEPSS 0.5% · 44th percentile
- 2026-10-23 20:14 UTCEG score recompute
- 2026-10-23 20:14 UTCGHSA enrichmentGHSA-mqc2-pwjw-2w78 · GitHub severity CRITICAL
- 2026-10-23 16:26 UTCEPSS rescoreEPSS 0.5% · 44th percentile
- 2026-10-22 19:14 UTCEG score recompute
- 2026-10-22 19:14 UTCGHSA enrichmentGHSA-mqc2-pwjw-2w78 · GitHub severity CRITICAL
- 2026-10-22 16:27 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
- 2026-10-21 18:15 UTCEG score recompute
- 2026-10-21 18:15 UTCGHSA enrichmentGHSA-mqc2-pwjw-2w78 · GitHub severity CRITICAL
- 2026-10-21 16:27 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
- 2026-10-20 17:16 UTCEG score recompute
- 2026-10-20 17:16 UTCGHSA enrichmentGHSA-mqc2-pwjw-2w78 · GitHub severity CRITICAL
- 2026-10-20 16:27 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
- 2026-10-19 16:26 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
- 2026-10-19 16:17 UTCEG score recompute
- 2026-10-19 16:16 UTCGHSA enrichmentGHSA-mqc2-pwjw-2w78 · GitHub severity CRITICAL
- 2026-10-18 16:27 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
- 2026-10-18 15:17 UTCGHSA enrichmentGHSA-mqc2-pwjw-2w78 · GitHub severity CRITICAL
- 2026-10-18 10:33 UTCEG score recompute
- 2026-10-17 16:27 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
- 2026-10-17 14:18 UTCEG score recompute
- 2026-10-17 14:18 UTCGHSA enrichmentGHSA-mqc2-pwjw-2w78 · GitHub severity CRITICAL
- 2026-10-16 16:29 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
- 2026-10-16 13:19 UTCEG score recompute
- 2026-10-16 13:19 UTCGHSA enrichmentGHSA-mqc2-pwjw-2w78 · GitHub severity CRITICAL
- 2026-10-15 16:26 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
- 2026-10-15 12:18 UTCEG score recompute
- 2026-10-15 12:18 UTCGHSA enrichmentGHSA-mqc2-pwjw-2w78 · GitHub severity CRITICAL
- 2026-10-14 16:27 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
- 2026-10-14 07:43 UTCEG score recompute
- 2026-10-14 07:42 UTCGHSA enrichmentGHSA-mqc2-pwjw-2w78 · GitHub severity CRITICAL
- 2026-10-13 16:27 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
- 2026-10-13 02:55 UTCGHSA enrichmentGHSA-mqc2-pwjw-2w78 · GitHub severity CRITICAL
- 2026-10-12 20:30 UTCEG score recompute
- 2026-10-12 16:28 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
- 2026-10-12 00:53 UTCEG score recompute
- 2026-10-11 13:41 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
- 2026-10-10 19:55 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
- 2026-10-09 20:02 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
- 2026-10-08 16:36 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
- 2026-10-07 23:41 UTCEPSS rescoreEPSS 0.5% · 42nd percentile
- 2026-10-06 15:12 UTCEPSS rescoreEPSS 0.5% · 42nd percentile
- 2026-10-05 17:38 UTCEPSS rescoreEPSS 0.5% · 42nd percentile
- 2026-10-04 23:18 UTCEPSS rescoreEPSS 0.5% · 42nd percentile
- 2026-10-03 14:21 UTCEPSS rescoreEPSS 0.5% · 42nd percentile
- 2026-09-30 14:59 UTCEPSS rescoreEPSS 0.5% · 42nd percentile
- 2026-09-30 09:32 UTCEG score recompute
- 2026-09-28 13:45 UTCEPSS rescoreEPSS 0.5% · 42nd percentile
- 2026-09-27 13:40 UTCEPSS rescoreEPSS 0.5% · 42nd percentile
- 2026-09-26 15:53 UTCEPSS rescoreEPSS 0.5% · 42nd percentile
- 2026-09-24 13:59 UTCEPSS rescoreEPSS 0.5% · 42nd percentile
- 2026-09-18 19:22 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
- 2026-09-17 19:22 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
- 2026-09-15 03:05 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
- 2026-09-13 16:42 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
- 2026-09-12 14:55 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
- 2026-09-11 09:31 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
- 2026-09-07 15:56 UTCEPSS rescoreEPSS 0.5% · 40th percentile
- 2026-09-06 13:43 UTCEPSS rescoreEPSS 0.5% · 40th percentile
- 2026-09-05 15:23 UTCEPSS rescoreEPSS 0.5% · 40th percentile
- 2026-09-04 13:56 UTCEPSS rescoreEPSS 0.5% · 40th percentile
- 2026-09-02 14:07 UTCEPSS rescoreEPSS 0.5% · 40th percentile
- 2026-09-01 03:31 UTCEPSS rescoreEPSS 0.5% · 40th percentile
- 2026-08-30 19:13 UTCEPSS rescoreEPSS 0.5% · 40th percentile
- 2026-08-27 14:21 UTCEPSS rescoreEPSS 0.5% · 40th percentile
- 2026-08-26 14:41 UTCEPSS rescoreEPSS 0.5% · 40th percentile
- 2026-08-25 13:44 UTCEPSS rescoreEPSS 0.5% · 40th percentile
- 2026-08-21 23:44 UTCEPSS rescoreEPSS 0.5% · 40th percentile
- 2026-08-20 22:51 UTCEPSS rescoreEPSS 0.5% · 40th percentile
- 2026-08-19 16:59 UTCEPSS rescoreEPSS 0.5% · 40th percentile
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Frequently asked(5)
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Dependency Blast Radius
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