CVE-2026-81868 is a medium-severity (CVSS 6.5) CWE-288 vulnerability in Steeltoe.Security.Authorization.Certificate. A fix is available for Steeltoe.Security.Authorization.Certificate — see the affected versions and patch details below.
Steeltoe: Header-forwarded client cert lacks proof of private-key possession
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-81868.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-81868 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 384,189 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
Steeltoe.Security.Authorization.CertificateReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects NuGet packages — download data is not available via public APIs for these ecosystems.
Description
Summary
When Steeltoe's certificate-based authorization (UseCertificateAuthorization) is configured, the default configuration of the middleware relies on the X-Client-Cert HTTP header to identify the client certificate, without verifying private-key possession. This header is not stripped by common Cloud Foundry routers (like Gorouter or Envoy) on inbound requests.
Impact
An attacker who obtains the public certificate of an application instance in the target organization or space can spoof the X-Client-Cert header. This allows the attacker to bypass SameOrg and SameSpace authorization policies, granting unauthorized access to protected endpoints for the duration of the certificate's validity period.
Affected configuration
- The application uses
AddOrgAndSpacePolicies()andUseCertificateAuthorization()for inter-service authorization. - Inbound requests are not restricted to a known trusted proxy source IP.
- The application's endpoints are network-accessible to the attacker (e.g., exposed to the internet via a public Cloud Foundry route, or the attacker has access to the internal Cloud Foundry network).
Mitigations
If an immediate upgrade to a patched version is not possible:
- Restrict
UseCertificateForwardingto trusted proxy source IPs usingForwardedHeadersOptions.KnownProxiesandKnownNetworks. - Change the forwarding header to
X-Forwarded-Client-Certso that Cloud Foundry Gorouter and Envoy header stripping mechanisms apply to inbound untrusted requests. - Add a secondary authorization layer (e.g., a shared secret or mutual TLS at the proxy layer) for sensitive endpoints.
- Ensure the application is not bound to a public route unless explicitly required. Use Cloud Foundry internal routes (e.g.,
.apps.internal) and container-to-container network policies to strictly limit network access to intended internal clients.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| .NETNuGet | Steeltoe.Security.Authorization.Certificate | all versions | 4.3.0dotnet add package Steeltoe.Security.Authorization.Certificate --version 4.3.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Steeltoe.Security.Authorization.Certificate, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update Steeltoe.Security.Authorization.Certificate to 4.3.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-81868 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Frequently Asked Questions
Is CVE-2026-81868 in your dependencies?
Find it across NuGet, including transitive dependencies.