Security Bulletin

Disclosure Details
CVSS Impact Score6.6 AV:N/AC:H/PR:H/UI:N/S:C/C:H/I:L/A:N/E:F/RL:O/RC:C
Affected Releases1.5 to 1.5.7
1.6 to 1.6.4
All releases prior to 1.5

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 *, Envoy incorrectly allows, when it should only allow

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 incorrectly accepts a certificate from an upstream peer with a Subject Alternative Name (SAN) of * Instead a SAN of * or should be present.

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

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.


  • 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.

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