What is the CVSS score of CVE-2020-9399?

CVE-2020-9399 has a CVSS 3.1 base score of 5.5 (Medium). CVSS vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N. EPSS exploitation probability: 1.1%.

Avast CVE-2020-9399

MEDIUM

Interpretation Conflict (CWE-436)

2020-02-28 cve@mitre.org

Authentication Bypass Antivirus Pro Avast Antivirus For Linux Antivirus Pro Plus

5.5

CVSS 3.1 · NVD

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Vulnerability Assessment

Weakness	CWE CWE-436 OWASP Top 10:2025 A06:2025 - Insecure Design ASVS 5.0 V4 - API and Web Service Interpretation consistency
Impact	CVSS score of 5.5 (MEDIUM). Attack characteristics: local attack vector, low complexity, no privileges required, user interaction required.
Exploit ScenarioDerived	Successful exploitation could compromise the medium-severity affected system.

This Month Plan within 30 days. Why: MEDIUM severity (CVSS 4.0-6.9).

No patch listed yet 1.1% exploitation probability (EPSS)

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AnalysisAI

The Avast AV parsing engine allows virus-detection bypass via a crafted ZIP archive. Rated medium severity (CVSS 5.5), this vulnerability is no authentication required, low attack complexity. No vendor patch available.

RemediationAI

No vendor patch is available at time of analysis. Monitor vendor advisories for updates. Apply vendor patches when available. Implement network segmentation and monitoring as interim mitigations.

Affects your stack

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Technical ContextAI · show details

This vulnerability is classified under CWE-436. The Avast AV parsing engine allows virus-detection bypass via a crafted ZIP archive. This affects versions before 12 definitions 200114-0 of Antivirus Pro, Antivirus Pro Plus, and Antivirus for Linux. Affected products include: Avast Antivirus For Linux, Avast Antivirus Pro, Avast Antivirus Pro Plus. Version information: before 12.

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Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

NVD PRIMARY 5.5 MEDIUM

AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

Attack Vector

Local

Attack Complexity

Low

Privileges Required

None

User Interaction

Required

Scope

Unchanged

Confidentiality

None

Integrity

High

Availability

None

DescriptionNVD

The Avast AV parsing engine allows virus-detection bypass via a crafted ZIP archive. This affects versions before 12 definitions 200114-0 of Antivirus Pro, Antivirus Pro Plus, and Antivirus for Linux.

Threat Intelligence Overview

EPSS Score

1.1%

Top 37% exploitable

Data Quality

2 sources

Confidence: Low

NVD

CVE.org

EPSS

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue

Severity MEDIUM

CISA KEV No

Public POC No

EPSS 1.1%

Patch available No

Active threat No

Deciding rule

MEDIUM severity (CVSS 4.0-6.9)

What every action level means

Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.

Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.

This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.

This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.

Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived

Defer

Exploitation· derived

None

System Exposure· derived

Small

Automatable· derived

Human Impact· derived

Medium

Priority Score

Low Medium High Critical

KEV: 0

EPSS: +1

CVSS: +28

PoC: 0

Weaponized: 0

Threat intel: 0

Gov advisory: 0

Attack Technique

Authentication Bypass CRITICAL

Authentication bypass attacks exploit flaws in the verification mechanisms that control access to systems and applications.

Affected Products (CPE)NVD

cpe:2.3:a:avast:antivirus_for_linux:*:*:*:*:*:*:*:*

cpe:2.3:a:avast:antivirus_pro:*:*:*:*:*:*:*:*

cpe:2.3:a:avast:antivirus_pro_plus:*:*:*:*:*:*:*:*

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Same weakness CWE-436 – Interpretation Conflict

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References

Advisories & patches

REF https://blog.zoller.lu/p/tzo-23-2020-avast-generic-archive.html REF https://seclists.org/fulldisclosure/2020/Feb/35

Search Externally

GitHub PoC

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