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EnvoyApplication · Envoyproxy

CVE-2021-32777

HIGH · 8.3 CVSS v3.1 Published 2021-08-24
Fix available
A fix is available. Upgrade to 1.16.5 / 1.17.4 or later.
See remediation →
92/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Envoy is an open source L7 proxy and communication bus designed for large modern service oriented architectures. In affected versions when ext-authz extension is sending request headers to the external authorization service it must merge multiple value headers according to the HTTP spec. However, only the last header value is sent. This may allow specifically crafted requests to bypass authorization. Attackers may be able to escalate privileges when using ext-authz extension or back end service that uses multiple value headers for authorization. A specifically constructed request may be delivered by an untrusted downstream peer in the presence of ext-authz extension. Envoy versions 1.19.1, 1.18.4, 1.17.4, 1.16.5 contain fixes to the ext-authz extension to correctly merge multiple request header values, when sending request for authorization.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

The ext-authz extension in Envoy fails to properly merge multiple header values according to HTTP specification when forwarding request headers to external authorization services. Instead of combining all values, only the last header value is sent, potentially allowing attackers to craft requests with specific header ordering to bypass authorization checks.

MitigationUpgrade Envoy to version 1.19.1, 1.18.4, 1.17.4, 1.16.5 or later which contain the fix for proper multi-value header merging in ext-authz.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
EnvoyApplication
Affected:>= 1.16.0, < 1.16.5>= 1.17.0, < 1.17.4>= 1.18.0, < 1.18.4= 1.19.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
Low

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Determine installed Envoy version
    Run 'envoy --version' or check the Envoy binary metadata
    Affected if The version is >= 1.16.0 and < 1.16.5, OR >= 1.17.0 and < 1.17.4, OR >= 1.18.0 and < 1.18.4, OR exactly 1.19.0
  2. Locate Envoy configuration file
    Find the Envoy bootstrap or xDS configuration file in use (commonly at /etc/envoy/envoy.yaml or referenced in Envoy process arguments)
    Affected if Configuration file exists and Envoy version is in the affected range
  3. Verify ext-authz filter is configured
    Search the Envoy configuration for 'ext_authz' or 'ext_authz_filter' in the http_filters or network_filters section
    Affected if The ext-authz filter is present in the configuration and Envoy version is in the affected range
  4. Confirm authorization service is configured
    Look for the 'ext_authz' cluster definition and 'http_service' or 'grpc_service' block that specifies the external authorization server endpoint
    Affected if An external authorization service is defined and Envoy version is in the affected range

You are affected if your Envoy version falls within the vulnerable ranges AND the ext-authz filter is configured to forward request headers to an external authorization service.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 1.16.5 / 1.17.4 / 1.18.4 or later
Fixed in 1.16.51.17.41.18.4
Interim mitigation

Upgrade Envoy to version 1.19.1, 1.18.4, 1.17.4, 1.16.5 or later which contain the fix for proper multi-value header merging in ext-authz.

Recommended fix High confidence

1.16.5, 1.17.4, 1.18.4, or 1.19.1 (matching your current minor version)

  1. Identify current Envoy version using envoy --version or equivalent
  2. For Envoy 1.16.x: upgrade to version 1.16.5
  3. For Envoy 1.17.x: upgrade to version 1.17.4
  4. For Envoy 1.18.x: upgrade to version 1.18.4
  5. For Envoy 1.19.0: upgrade to version 1.19.1
  6. Restart Envoy service to load the new version
  7. Verify the ext-authz extension now correctly merges multiple header values when sending authorization requests
Caveat Patch upgrades within same minor version typically have minimal breaking changes; consult Envoy release notes if crossing minor versions

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Envoy Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA2.0 h
20.0 hours of engineering $3,500
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-32777 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data