# CVE-2026-81515: Steeltoe Eureka Discovery Client denial of service via malformed registry fields

Source: https://junglewise.ai/threats/cve-2026-81515-steeltoe-eureka-discovery-client-denial-of-service-via-malformed  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-17. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-81515 · Severity: high · CVSS 7.5 · Published 2026-09-17

Steeltoe's Eureka discovery client is used by .NET applications to locate and connect to other services in a microservices architecture. A malformed field value in any service registration (such as an unrecognized action type or invalid timestamp) causes the entire registry to fail to deserialize, leaving all connected applications without access to the service registry and unable to discover dependent services until the bad registration is manually removed.

Technologies: [Steeltoe.Discovery.Eureka (NuGet)](https://junglewise.ai/threats/technologies/nuget-steeltoe-discovery-eureka). Vendors: [NuGet](https://junglewise.ai/threats/vendors/nuget).

## Quick answers

**Is CVE-2026-81515 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-81515 being exploited in the wild.

**How severe is CVE-2026-81515?** High severity, with a CVSS score of 7.5, published 17 September 2026.

**Which products and versions are affected?** Steeltoe.Discovery.Eureka (NuGet) ECOSYSTEM:introduced=4.0.0,fixed=4.3.0.

**Is there a fix for CVE-2026-81515?** Yes. Steeltoe.Discovery.Eureka (NuGet): upgrade to 4.3.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-81515 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-81515?** Check whether you run Steeltoe.Discovery.Eureka (NuGet) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Steeltoe.Discovery.Eureka (NuGet): upgrade to 4.3.0 or later

  ```sh
  dotnet add package Steeltoe.Discovery.Eureka --version 4.3.0
  ```


## Technical details

The vulnerability is a deserialization failure in Steeltoe's Eureka discovery client that treats the entire registry response as a monolithic unit. When a service instance contains a field that fails to parse—such as an unrecognized `actionType` enum value, a non-boolean value for `isCoordinatingDiscoveryServer`, or a malformed timestamp—the entire deserialization operation aborts. This causes all Steeltoe clients connected to that registry to receive an empty or stale instance list, effectively disabling service discovery. The vulnerability requires write access to the Eureka registration API and is more likely to occur in mixed-platform environments where Java, Spring, or other non-.NET clients may register instances with unexpected field formats. A patch addressing this specific issue is available; as a mitigation, operators should audit the registry for non-standard field values and restrict write access to trusted services.

## Affected products

- Steeltoe Discovery.Eureka unspecified

## Identifiers

- CVE-2026-81515
- GHSA-hr73-3gpv-hh6q

## Timeline

- 2026-09-17: disclosed
- other: Related but distinct from CVE-2026-50196 addressing DataCenterInfo.name field

## Related threats

- [Steeltoe.Discovery.Eureka Denial of Service via Registry Poisoning](https://junglewise.ai/threats/cve-2026-50196-steeltoe-discovery-eureka-denial-of-service-via-registry)
- [Steeltoe Leaks Basic Auth Credentials to Logs After Fetch Registry Error](https://junglewise.ai/threats/cve-2024-40636-steeltoe-leaks-basic-auth-credentials-to-logs-after-fetch)