CVE-2026-54776

CoreWCF: Unix Domain Socket PosixIdentity transport accepts connections that skip the security upgrade

Workarounds

Restrict filesystem access to the UDS socket file using owner/group/mode (e.g. chmod 0660 plus a dedicated group) so that only the POSIX users who are already authorized to invoke the service can connect at all. This makes the missing-upgrade behaviour equivalent to the operating system’s filesystem permissions instead of relying on framing-layer identity checks.
Avoid relying on ServiceSecurityContext.PrimaryIdentity for authorization decisions, or back it up with an authentication-required authorization policy that rejects anonymous principals.

A CoreWCF service hosted on Unix Domain Sockets with the PosixIdentity client credential type (UnixDomainSocketBinding with Security.Mode = TransportCredentialOnly and Security.Transport.ClientCredentialType = PosixIdentity) does not require the client to perform the application/unixposix stream upgrade before dispatching messages.

A critical operation is accessible without requiring any authentication. Typical impact: any user can invoke the privileged function.

CVE-2026-54776 has a CVSS score of 4.4 (Medium). The vector is requires local access, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.8.1, 1.9.1); upgrading removes the vulnerable code path.

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Fixed in CoreWCF v1.8.1 and v1.9.1

1. What is CVE-2026-54776? CVE-2026-54776 is a medium-severity missing authentication for critical function vulnerability in CoreWCF.UnixDomainSocket (nuget), affecting versions < 1.8.1. It is fixed in 1.8.1, 1.9.1. A critical operation is accessible without requiring any authentication.
2. How severe is CVE-2026-54776? CVE-2026-54776 has a CVSS score of 4.4 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of CoreWCF.UnixDomainSocket are affected by CVE-2026-54776? CoreWCF.UnixDomainSocket (nuget) versions < 1.8.1 is affected.
4. Is there a fix for CVE-2026-54776? Yes. CVE-2026-54776 is fixed in 1.8.1, 1.9.1. Upgrade to this version or later.
5. Is CVE-2026-54776 exploitable, and should I be worried? Whether CVE-2026-54776 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-54776 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-54776?
   • Upgrade CoreWCF.UnixDomainSocket to 1.8.1 or later
   • Upgrade CoreWCF.UnixDomainSocket to 1.9.1 or later

Other vulnerabilities in CoreWCF.UnixDomainSocket