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

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

4.4 · CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N

EPSS

• CVE-2026-54776: 0.15% estimated exploitation activity in the next 30 days; percentile 4.35 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact 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. Patches Fixed in CoreWCF v1.8.1 and v1.9.1 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.

Published by the source

19 Jun 2026, 20:46 UTC

Last modified by the source

19 Jun 2026, 20:46 UTC

Source last checked

26 Oct 2026, 17:04 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-wjpq-6766-7f5j

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# Patch Next advisory brief: CVE-2026-54776

Advisory: CoreWCF: Unix Domain Socket PosixIdentity transport accepts connections that skip the security upgrade
IDs: CVE-2026-54776, GHSA-wjpq-6766-7f5j
Record: https://patchnext.com/advisories/cve-2026-54776 (revision 1, source checked 26 Oct 2026, 17:04 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.4)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: corewcf.unixdomainsocket 1.9.1, 1.8.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- NuGet corewcf.unixdomainsocket: affected < 1.8.1; >= 1.9.0, < 1.9.1; fixed in 1.8.1, 1.9.1

## Suggested inspection (read-only)
- NuGet corewcf.unixdomainsocket: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on corewcf.unixdomainsocket.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-wjpq-6766-7f5j (GitHub-reviewed advisory GHSA-wjpq-6766-7f5j lists affected ranges: NuGet corewcf.unixdomainsocket >=0 =1.9.0 <1.9.1)

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