Steeltoe.Discovery.Eureka: malformed enum/bool/timestamp field aborts entire registry fetch (DoS)

Steeltoe's Eureka discovery client deserializes the registry response as a single unit. If any registered instance contains a field value that cannot be parsed (for example, an unrecognized actionType, a non-boolean value for isCoordinatingDiscoveryServer, or a non-numeric timestamp), deserialization of the entire registry fails. All Steeltoe Eureka clients connected to that registry then receive an empty or stale instance list until the malformed registration is removed.

This is a related but distinct issue from CVE-2026-50196, which addressed only the DataCenterInfo.name field.

Any principal that can register or update a service instance in the Eureka registry can trigger a service-discovery outage for all Steeltoe applications connected to the same registry. The outage persists until the offending registration is removed.

• Application uses EurekaDiscoveryClient (any deployment, including self-hosted Eureka).
• The registry contains at least one service instance with an unrecognized value in a field such as actionType, status, isCoordinatingDiscoveryServer, or timestamp fields.
• Mixed-platform environments — for example, Java or Spring services co-existing in the same Eureka registry — are more likely to encounter this condition.

If an immediate upgrade is not possible:

• Audit the Eureka registry for registrations containing non-standard field values, particularly those originating from non-.NET clients.
• Restrict write access to the Eureka registration API to trusted services.