Steeltoe vulnerable to management-port isolation bypass via spoofed Host header

published 2026-06-17 4 mo ago modified 2026-07-02 4 mo ago also GHSA-58f6-6rj2-3v8r , EUVD-2026-37801

cvss: 8.2; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.2%; EPSS 0.2% chance of exploitation in 30 days, percentile 14%
public exploits: 0; none known

Steeltoe is an open source project that provides a collection of libraries that helps users build cloud-native applications. When Steeltoe management endpoints versions 3.2.2 through 3.3.0 and 4.1.0 are configured to listen on an alternate port (`Management:Endpoints:Port` is configured), the middleware responsible for restricting access to the endpoints uses the `Host` HTTP header rather than the actual network socket port. Versions 3.4.0 and 4.2.0 patch the issue. If an immediate upgrade to a patched version is not possible, add explicit ASP.NET Core authorization (`RequireAuthorization`) to all sensitive actuator endpoints as a defense-in-depth measure independent of port isolation and/or configure the reverse proxy or load balancer to enforce the `Host` header value and prevent clients from setting an arbitrary port.

Patch / fix

fixed in 2 links 2

nuget Steeltoe.Management.Endpoint 4.2.0
nuget Steeltoe.Management.EndpointCore 3.4.0

github.com/SteeltoeOSS/Steeltoe@4cbc352 commit
github.com/SteeltoeOSS/Steeltoe@b7ca93c commit

CISA SSVC

Exploitation: none
Automatable: yes
Technical impact: partial
Assessed: 4 mo ago (2026-06-18)

Exploit prediction

0.24% chance of exploitation in the next 30 days, higher than 14% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	8.2	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N
GitHub	3.1	8.2	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N

Affected packages

ecosystem	package	affected	fixed in
nuget	Steeltoe.Management.Endpoint	<4.2.0	4.2.0
nuget	Steeltoe.Management.EndpointCore	>=3.2.2, <3.4.0	3.4.0

Affected products

SteeltoeOSS Steeltoe.Management.Endpoint
SteeltoeOSS Steeltoe.Management.EndpointCore

Classification

Weakness

CWE-288 Authentication Bypass Using an Alternate Path or Channel
CWE-639 Authorization Bypass Through User-Controlled Key

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary