CVE-2018-16886
Description
Etcd, versions 3.2.0 through 3.2.25 and 3.3.0 through 3.3.10, are vulnerable to an improper authentication issue when role-based access control (RBAC) is used and client-cert-auth is enabled. If an etcd client server's TLS certificate contains a Common Name (CN) which matches a valid RBAC username, a remote attacker may authenticate as that user with any valid (trusted) client certificate in a REST API request to the gRPC-gateway.
Statement
OpenShift Container Platform 3.x, and 4.1 versions do not use etcd Role-based access control so they are not affected.
Mitigation
Ensure that the client server TLS certificate (specified in --cert-file argument or ETCD_CERT_FILE environment variable) does not include a CN (Common Name) field. If a Common Name field is part of this certificate, replace it with one which omits it.
To check the CN field of a certificate:
openssl x509 -noout -subject -in /path/to/client.crt | grep -o 'CN.*'
To check if there is a username matching the CN field in the TLS client certificate:
etcdctl user get <TLS client certificate CN>
For more information on TLS authentication features including how client-cert-auth is enabled, refer to the etcd transport security model documentation: https://github.com/etcd-io/etcd/blob/master/Documentation/op-guide/security.md
For more information on Role-based access control including how it is enabled, refer to the etcd role-based access control documentation: https://github.com/etcd-io/etcd/blob/master/Documentation/op-guide/authentication.md
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 6.8 | 8.1 | N/A |
| Attack Vector | Network | Network | N/A |
| Attack Complexity | High | High | N/A |
| Privileges Required | Low | None | N/A |
| User Interaction | None | None | N/A |
| Scope | Unchanged | Unchanged | N/A |
| Confidentiality | High | High | N/A |
| Integrity Impact | High | High | N/A |
| Availability Impact | None | High | N/A |
Vector
Red Hat: CVSS:3.0/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N
NVD: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Understanding the Weakness (CWE)
Integrity,Confidentiality,Availability,Access Control
Technical Impact: Read Application Data; Gain Privileges or Assume Identity; Execute Unauthorized Code or Commands
This weakness can lead to the exposure of resources or functionality to unintended actors, possibly providing attackers with sensitive information or even execute arbitrary code.
Acknowledgements
Red Hat would like to thank Matt Wheeler (Osirium) for reporting this issue.
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