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](http://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 security@kubernetes.io
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