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
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.
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.
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).
If you find evidence that this vulnerability has been exploited, please contact firstname.lastname@example.org
See ingress-nginx Issue #8686 for more details.
This vulnerability was reported by Gafnit Amiga.
CJ Cullen on behalf of the Kubernetes Security Response Committee