ISTIO-SECURITY-2020-008

Istio is vulnerable to a newly discovered vulnerability:

• CVE-2020-15104: When validating TLS certificates, Envoy incorrectly allows a wildcard DNS Subject Alternative Name apply to multiple subdomains. For example, with a SAN of *.example.com, Envoy incorrectly allows nested.subdomain.example.com, when it should only allow subdomain.example.com.
  • CVSS Score: 6.6 AV:N/AC:H/PR:H/UI:N/S:C/C:H/I:L/A:N/E:F/RL:O/RC:C

Istio users are exposed to this vulnerability in the following ways:

• Direct use of Envoy’s verify_subject_alt_name and match_subject_alt_names configuration via Envoy Filter.

• Use of Istio’s subjectAltNames field in destination rules with client TLS settings. A destination rule with a subjectAltNames field containing nested.subdomain.example.com incorrectly accepts a certificate from an upstream peer with a Subject Alternative Name (SAN) of *.example.com. Instead a SAN of *.subdomain.example.com or nested.subdomain.example.com should be present.

• Use of Istio’s subjectAltNames in service entries. A service entry with a subjectAltNames field with a value similar to nested.subdomain.example.com incorrectly accepts a certificate from an upstream peer with a SAN of *.example.com.

The Istio CA, which was formerly known as Citadel, does not issue certificates with DNS wildcard SANs. The vulnerability only impacts configurations that validate externally issued certificates.

Mitigation

• For Istio 1.5.x deployments: update to Istio 1.5.8 or later.
• For Istio 1.6.x deployments: update to Istio 1.6.5 or later.

Reporting vulnerabilities

We’d like to remind our community to follow the vulnerability reporting process to report any bug that can result in a security vulnerability.