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EnvoyApplication · Envoyproxy

CVE-2021-32779

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 envoy incorrectly handled a URI '#fragment' element as part of the path element. Envoy is configured with an RBAC filter for authorization or similar mechanism with an explicit case of a final "/admin" path element, or is using a negative assertion with final path element of "/admin". The client sends request to "/app1/admin#foo". In Envoy prior to 1.18.0, or 1.18.0+ configured with path_normalization=false. Envoy treats fragment as a suffix of the query string when present, or as a suffix of the path when query string is absent, so it evaluates the final path element as "/admin#foo" and mismatches with the configured "/admin" path element. In Envoy 1.18.0+ configured with path_normalization=true. Envoy transforms this to /app1/admin%23foo and mismatches with the configured /admin prefix. The resulting URI is sent to the next server-agent with the offending "#foo" fragment which violates RFC3986 or with the nonsensical "%23foo" text appended. A specifically constructed request with URI containing '#fragment' element delivered by an untrusted client in the presence of path based request authorization resulting in escalation of Privileges when path based request authorization extensions. Envoy versions 1.19.1, 1.18.4, 1.17.4, 1.16.5 contain fixes that removes fragment from URI path in incoming requests.

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

Envoy incorrectly processes URI fragments ('#fragment') as part of the path element, causing authorization bypass. When a client sends a request to '/app1/admin#foo', Envoy evaluates the final path as '/admin#foo' (pre-1.18.0 or with path_normalization=false) or '/app1/admin%23foo' (1.18.0+ with path_normalization=true), allowing requests to bypass RBAC filters configured to match '/admin' path elements.

MitigationUpgrade Envoy to version 1.19.1, 1.18.4, 1.17.4, or 1.16.5 which contain fixes that remove fragments from the URI path in incoming requests.

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. Identify Envoy version
    Run 'envoy --version' or check the Envoy container/image metadata to obtain the installed version number
    Affected if The version falls within any of these ranges: >=1.16.0 and <1.16.5, >=1.17.0 and <1.17.4, >=1.18.0 and <1.18.4, or equals 1.19.0
  2. Locate Envoy configuration
    Find the Envoy bootstrap or xDS configuration file (typically envoy.yaml, bootstrap.yaml, or delivered via xDS) that defines the Envoy instance
    Affected if Configuration file cannot be located for inspection
  3. Check if RBAC filter is active
    Inspect the Envoy configuration for 'rbac' filter in the http_filters or network_filters section. Look for RBAC policies that match specific path patterns such as '/admin'
    Affected if RBAC filter is configured with path-based policies and the Envoy version is affected by this CVE
  4. Verify path_normalization setting
    In the Envoy configuration, search for the 'path_normalization' setting within the RouteConfiguration or HttpConnectionManager. If not explicitly set, it defaults to true in 1.18.0+ and false in earlier versions
    Affected if path_normalization is set to false (pre-1.18 behavior) or is unset while running an affected 1.16.x or 1.17.x version
  5. Test for fragment bypass
    Send an HTTP request to Envoy with a URI containing a fragment, such as GET /app1/admin#foo. Compare the path that Envoy matches against RBAC policies. For pre-1.18 or path_normalization=false, observe if Envoy uses '/admin#foo'. For 1.18+ with path_normalization=true, observe if Envoy uses '/app1/admin%23foo'
    Affected if The effective path used for RBAC evaluation differs from the expected '/admin' path, allowing access that should be denied

You are affected if your Envoy version is in the affected ranges AND you have RBAC filters configured with path-based policies, as the fragment can cause path matching to fail and bypass authorization checks.

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, or 1.16.5 which contain fixes that remove fragments from the URI path in incoming requests.

Recommended fix High confidence

1.16.5, 1.17.4, 1.18.4, or 1.19.1 depending on current version branch

  1. 1. Identify the current Envoy version by running 'envoy --version' or checking the deployment configuration
  2. 2. Based on the current version, upgrade to the corresponding fixed release: if running 1.16.x (where x >= 0), upgrade to 1.16.5; if running 1.17.x, upgrade to 1.17.4; if running 1.18.x, upgrade to 1.18.4; if running 1.19.0, upgrade to 1.19.1
  3. 3. For Envoy 1.18.0+ with path_normalization=true, the fix transforms #fragment to %23 encoding and mismatches the configured path; upgrading to the fixed version removes the fragment from the URI path entirely
  4. 4. After upgrade, verify RBAC or authorization policies still work as expected with paths like '/admin'
  5. 5. Test with a request containing '#fragment' (e.g., '/app1/admin#foo') to confirm the fragment is now properly handled and authorization is enforced correctly
Caveat Minimal; the fix removes fragment from URI path before authorization, which may affect any non-standard clients relying on fragments being preserved in requests

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

Fix this in Envoy Scoped from the published advisory
  • Consultation3.0 h
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
13.0 hours of engineering $2,280
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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

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