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Nginx Ingress ControllerWeb server / proxy · F5

CVE-2021-23055

MEDIUM · 6.5 CVSS v3.1 Published 2022-04-21
Fix available
A fix is available. Upgrade to 1.12.3 / 2.0.3 or later.
See remediation →
71/100
Remediation priority · Elevated
Remotely reachable 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
On version 2.x before 2.0.3 and 1.x before 1.12.3, the command line restriction that controls snippet use with NGINX Ingress Controller does not apply to Ingress objects. Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.

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 NGINX Ingress Controller has a command-line flag to restrict NGINX snippet usage for security, but this restriction is not enforced when snippets are defined in Ingress objects, allowing a bypass of the intended security control. An attacker with permission to create or modify Ingress resources could potentially inject malicious NGINX configuration through snippets despite the command-line restriction being enabled.

MitigationUpgrade NGINX Ingress Controller to version 2.0.3+ (2.x) or 1.12.3+ (1.x). As a compensating control, review existing Ingress objects for unauthorized snippet usage and consider using Kubernetes admission policies to block Ingress resources containing snippets.

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
Nginx Ingress ControllerWeb server / proxy
Affected:>= 1.0.0, < 1.12.3>= 2.0.0, < 2.0.3

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
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

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

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 installed Nginx Ingress Controller version
    Run 'kubectl get pods -n <ingress-namespace> -o jsonpath="{.items[*].spec.containers[*].image}"' or check the deployment image. For Helm deployments, run 'helm list -A' and inspect the chart version.
    Affected if The installed version is >=1.0.0 and <1.12.3, or >=2.0.0 and <2.0.3
  2. Check if Ingress resources contain snippet annotations
    Run 'kubectl get ingress --all-namespaces -o json' and search for annotations containing 'snippet' or the nginx.ingress.kubernetes.io/configuration-snippet key.
    Affected if Any Ingress object has nginx.ingress.kubernetes.io/configuration-snippet or nginx.ingress.kubernetes.io/server-snippet annotations defined
  3. Verify the command-line security flag is configured
    Inspect the Ingress Controller deployment/daemonset: 'kubectl get deploy -n <ingress-namespace> -o json' and check spec.template.spec.containers[].command for flags like --annotations-snippet or verify if the ConfigMap enables allow-snippet-annotations.
    Affected if The --annotations-snippet flag is set to 'true' or the ConfigMap has allow-snippet-annotations: true, and Ingress resources contain snippets despite this setting
  4. Inspect Ingress objects for injected configuration
    Review all Ingress resources in the cluster for any unexpected or suspicious content within snippet annotations, comparing against expected legitimate snippets.
    Affected if Ingress resources contain snippets that should have been blocked by the command-line restriction but were applied to NGINX configuration

You are affected if your Nginx Ingress Controller version falls within the vulnerable ranges AND you have Ingress resources with snippet annotations that bypass the intended command-line restriction.

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 1.12.3 / 2.0.3 or later
Fixed in 1.12.32.0.3
Interim mitigation

Upgrade NGINX Ingress Controller to version 2.0.3+ (2.x) or 1.12.3+ (1.x). As a compensating control, review existing Ingress objects for unauthorized snippet usage and consider using Kubernetes admission policies to block Ingress resources containing snippets.

Recommended fix High confidence

1.12.3 (1.x branch) or 2.0.3 (2.x branch)

  1. Upgrade Nginx Ingress Controller to version 1.12.3 or later for the 1.x branch
  2. Alternatively, upgrade to version 2.0.3 or later for the 2.x branch
  3. After upgrade, verify that snippet restrictions are properly enforced for Ingress objects by testing your Ingress configurations
Caveat Review release notes for any configuration changes between your current version and the target version

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

Fix this in Nginx Ingress Controller Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA2.0 h
18.0 hours of engineering $3,200
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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-2021-23055 in production — separate from our analysis above.

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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