CVE-2020-9399

Malware-detection bypass via manipulated ZIP flag

Published Feb 28, 2020 · Updated Aug 4, 2024

Interpretation conflict in Avast antivirus products before 12 allows attackers to bypass malware detection with a crafted ZIP archive. The ZIP unpacker interprets a manipulated general-purpose flag differently from standard archive tools, cannot scan the container, and labels it clean. The bypass requires a user or downstream service to access the archive; embedded malicious content passes inspection, but the flaw does not itself execute it.

CVSS severity5.5
Medium
EPSS probability1.16%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Interpretation conflict in Avast antivirus products before 12 allows attackers to bypass malware detection with a crafted ZIP archive. The ZIP unpacker interprets a manipulated general-purpose flag differently from standard archive tools, cannot scan the container, and labels it clean. The bypass requires a user or downstream service to access the archive; embedded malicious content passes inspection, but the flaw does not itself execute it.

The record

CVE
CVE-2020-9399
Published
Feb 28, 2020
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-436, T1027
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 28, 2020CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

5.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N
4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:P/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-436Interpretation Conflict
T1027Obfuscated Files or Information

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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