Issue Details

A security issue was discovered in ingress-nginx where a user that can create or update ingress objects can use a newline character to bypass the sanitization of the spec.rules[].http.paths[].path field of an Ingress object (in the networking.k8s.io or extensions API group) to obtain the credentials of the ingress-nginx controller. In the default configuration, that credential has access to all secrets in the cluster.

This issue has been rated High (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:L), and assigned CVE-2021-25748.

Affected Components and Configurations

This bug affects ingress-nginx. If you do not have ingress-nginx installed on your cluster, you are not affected. You can check this by running kubectl get po -n ingress-nginx.

If you are running the “chrooted” ingress-nginx controller introduced in v1.2.0 (gcr.io/k8s-staging-ingress-nginx/controller-chroot), you are not affected.

Multitenant environments where non-admin users have permissions to create Ingress objects are most affected by this issue.

Affected Versions

<v1.2.1

Fixed Versions

v1.2.1

Mitigation

If you are unable to roll out the fix, this vulnerability can be mitigated by implementing an admission policy that restricts the spec.rules[].http.paths[].path field on the networking.k8s.io/Ingress resource to known safe characters (see the newly added rules, or the suggested value for annotation-value-word-blocklist).

Detection

If you find evidence that this vulnerability has been exploited, please contact [email protected]

Additional Details

See ingress-nginx Issue #8686 for more details.

Acknowledgements

This vulnerability was reported by Gafnit Amiga.

Thank You,
CJ Cullen on behalf of the Kubernetes Security Response Committee