content/en/news/security/istio-security-2020-008/index.md
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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.
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.
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