Steeltoe.Discovery.Consul: malformed 'secure' metadata aborts service instance lookup (DoS)

Summary

Steeltoe's Consul discovery client parses the secure metadata field on each registered service instance using bool.Parse, which throws on any value other than true or false. A single service instance registered with a malformed secure value (for example yes or 1) aborts construction of the entire instance list for that service, making the service undiscoverable. When GetAllInstancesAsync is used, one malformed instance in any service can abort enumeration across all services. This is the same "one malformed field aborts the whole batch" availability class as CVE-2026-50196, but affecting the Consul discovery client.

Impact

Any principal that can register a service in the Consul catalog can trigger a service-discovery outage for all Steeltoe applications resolving that service. The outage affects all instances of the targeted service — not just the malformed one — and persists until the offending registration is removed.

Affected configuration

• Application uses ConsulDiscoveryClient (any deployment).
• The Consul catalog contains at least one service instance with a secure metadata value that is not true or false.
• Mixed-platform environments where non-.NET clients register services with non-standard metadata values are more likely to encounter this condition.

Mitigations

If an immediate upgrade is not possible:

• Audit the Consul catalog for service registrations with non-standard secure metadata values.
• Restrict write access to the Consul service registration API to trusted services.