CVE-2016-20021Network attack vector

Arbitrary code execution via unverified repository snapshots

Published Jan 12, 2024 · Updated Jun 3, 2025

Cryptographic signature bypass in Gentoo Portage before 3.0.47 allows man-in-the-middle attackers to inject code into the package tree. The standalone emerge-webrsync utility downloads a .gpgsig file for the repository snapshot but installs the snapshot without verifying that signature. Exposure requires use of emerge-webrsync and an attacker positioned to alter its download; other Portage synchronization methods are not affected.

CVSS severity9.8
Critical
EPSS probability0.47%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cryptographic signature bypass in Gentoo Portage before 3.0.47 allows man-in-the-middle attackers to inject code into the package tree. The standalone emerge-webrsync utility downloads a .gpgsig file for the repository snapshot but installs the snapshot without verifying that signature. Exposure requires use of emerge-webrsync and an attacker positioned to alter its download; other Portage synchronization methods are not affected.

The record

CVE
CVE-2016-20021
Published
Jan 12, 2024
Updated
Jun 3, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-347, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 12, 2024CVE publishedPublication date reported by the CVE source.
  2. Jun 3, 2025Record 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 vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
9.8CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

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)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-347Improper Verification of Cryptographic Signature
T1557Adversary-in-the-Middle

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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