Nginx Ingress ControllerWeb server / proxy · F5
CVE-2026-55723
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 · uneditedWhen NGINX Ingress Controller is configured with Custom Resource Definitions (CRDs) or Ingress annotations, an injection vulnerability exists in the configuration generator of NGINX Ingress Controller. Multiple user-controllable fields are written into the generated NGINX configuration without sanitization. An authenticated attacker with permission to create or modify these CRDs or annotations may craft values that inject arbitrary NGINX configuration directives. Impact: An authenticated attacker granted write access to NGINX Ingress Controller CRDs or Ingress annotations through the Kubernetes API may be able to inject arbitrary NGINX configuration directives, create or delete files, or disable services. There is no data plane exposure; this is a control plane issue only. 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 confidenceNGINX Ingress Controller's configuration generator writes user-controllable fields from CRDs and Ingress annotations into generated NGINX configuration without sanitization. An authenticated attacker with permissions to create or modify these Kubernetes resources can inject arbitrary NGINX directives through specially crafted values, potentially creating/deleting files or disabling services.
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
>= 3.6.0, <= 3.7.2>= 4.0.0, <= 4.0.1>= 5.0.0, < 5.5.2CVSS 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
- High
- Availability
- Low
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/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 checksWork through these to decide whether this CVE applies to you.
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Identify NGINX Ingress Controller versionRun 'kubectl get deployment -n ingress-nginx ingress-nginx-controller -o jsonpath="{.spec.template.spec.containers[0].image}"' or check the Helm chart/app version in your clusterAffected if The installed version falls within >= 3.6.0 and <= 3.7.2, OR >= 4.0.0 and <= 4.0.1, OR >= 5.0.0 and < 5.5.2
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Review Ingress resources for suspicious annotationsRun 'kubectl get ingress -A -o yaml' and inspect all annotations, looking for values containing nginx.conf directives, semicolons, or unusual configuration patternsAffected if Any Ingress resource contains annotation values with NGINX directive syntax (e.g., 'nginx.ingress.kubernetes.io/configuration-snippet' or custom annotations with content like 'deny all;' or file operations)
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Examine NGINX Ingress Controller CRDsList custom resources (e.g., VirtualServer, TransportServer, Policy from the k8s.nginx.org API) with 'kubectl get <crd-kind> -A -o yaml' and inspect spec fields for unescaped directive contentAffected if Any CRD resource contains spec fields with raw NGINX directive strings that could be injected without sanitization
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Verify RBAC permissions on Ingress and CRD resourcesReview who can create or modify Ingress and NGINX Ingress CRDs using 'kubectl auth can-i create ingresses --as=<user>' or inspect ClusterRole/Role bindingsAffected if Untrusted or unauthorized users have create/update permissions on Ingress or NGINX Ingress Controller CRDs in your cluster
You are affected if your NGINX Ingress Controller version is within the vulnerable ranges AND untrusted users can create or modify Ingress resources or NGINX Ingress CRDs with injection-prone annotations or fields.
Generated from the published advisory. Verify against your own configuration.
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 · scoped5.5.2
Restrict write access to NGINX Ingress Controller CRDs and Ingress resources to trusted users only; review existing CRDs and Ingress resources for suspicious annotation values; apply vendor patch when available.
NGINX Ingress Controller version 5.5.2 or later (for v5.x); for v3.x and v4.x branches, upgrade to the latest supported version per F5's guidance
- Confirm current NGINX Ingress Controller version by running: kubectl get pods -n <ingress-namespace> -o jsonpath='{.items[0].spec.containers[0].image}'
- Identify all custom CRDs (TransportServer, GlobalConfiguration, etc.) and Ingress resources that may contain user-controllable annotations
- Review CRD and Ingress definitions for any custom annotations or fields that could be used for configuration injection
- Upgrade NGINX Ingress Controller to version 5.5.2 or later (for v5.x branches), or to the latest patch version in your supported branch
- After upgrade, verify the controller is running: kubectl get pods -n <ingress-namespace>
- Test that existing Ingress resources and CRDs still function correctly
- Review F5 advisory (my.f5.com) for any additional post-upgrade configuration requirements
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Nginx Ingress Controller
Scoped from the published advisory
- Consultation6.0 h
- Implementation12.0 h
- Testing6.0 h
- Review / QA4.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $7,968.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-55723 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-55723 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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