CVE-2021-32783Network attack vector

Envoy shutdown via ExternalName loopback proxying

Published Jul 23, 2021 · Updated Aug 3, 2024

Authorization bypass in Project Contour's Contour before 1.17.1 allows remote authenticated users to access Envoy's admin interface. Contour accepts a crafted ExternalName Service that resolves to loopback and builds an Envoy route to its localhost-only admin listener. Kubernetes permission to create Services is required; access enables Envoy shutdown, traffic draining or rerouting, and secret-metadata disclosure but not secret contents.

CVSS severity8.5
High
EPSS probability1.15%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authorization bypass in Project Contour's Contour before 1.17.1 allows remote authenticated users to access Envoy's admin interface. Contour accepts a crafted ExternalName Service that resolves to loopback and builds an Envoy route to its localhost-only admin listener. Kubernetes permission to create Services is required; access enables Envoy shutdown, traffic draining or rerouting, and secret-metadata disclosure but not secret contents.

The record

CVE
CVE-2021-32783
Published
Jul 23, 2021
Updated
Aug 3, 2024
Vendor
Project Contour
Product
Contour
Classifications
CWE-441, T1489
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jul 23, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 1.17.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Project Contour · Contourversion=< 1.17.1

Published CVSS scores

8.5GitHubCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:N/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-441Unintended Proxy or Intermediary ('Confused Deputy')
T1489Service Stop

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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