# CVE-2026-54781 — CoreWCF

> As of 2026-07-09, CVE-2026-54781 is a HIGH-severity vulnerability in CoreWCF, CVSS v3.1 7.4, EPSS 0.1% (7.5th percentile). No Threadlinqs-tracked threat campaign has been attributed to CVE-2026-54781 as of 2026-07-09; the identifier is re-checked against the Threadlinqs threat corpus on every daily ingest.

**Last updated:** 2026-07-09

## What is CVE-2026-54781?

CoreWCF is a port of the service side of Windows Communication Foundation (WCF) to .NET Core. Prior to 1.8.1 and 1.9.1, CoreWCF SAML token validation does not enforce SubjectConfirmation method URIs or holder-of-key proof keys in SamlSecurityTokenHandler, allowing holder-of-key downgrade or custom confirmation method assertions to authenticate a subject without proving authority over the assertion. This issue is fixed in versions 1.8.1 and 1.9.1.

The record classifies CVE-2026-54781 under weakness classes [CWE-287](https://intel.threadlinqs.com/cwe/CWE-287), [CWE-345](https://intel.threadlinqs.com/cwe/CWE-345). Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs no user interaction, and has high impact on confidentiality, integrity. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 89 days ago.

## Severity and exploitation probability

- **CVSS v3.1 base score:** 7.4 — HIGH (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N`)
- **EPSS (FIRST):** 0.1% probability of exploitation in the next 30 days, higher than 7.5% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 4/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-07-08, last modified 2026-07-09

## Is CVE-2026-54781 being exploited?

It currently carries a trending score of 31 in the Threadlinqs vulnerability feed.

## Affected products and versions

- [CoreWCF](https://intel.threadlinqs.com/vendors/corewcf): CoreWCF

## How to fix CVE-2026-54781

No vendor patch reference has been recorded for CVE-2026-54781 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

## Threat activity tracking CVE-2026-54781

No threat campaign in the Threadlinqs corpus currently references CVE-2026-54781, in its CVE list or as an indicator. The linkage is recomputed from the live corpus on every daily ingest, so this section fills in as soon as a tracked campaign cites the identifier.

## Sources

Enriched from CVE.org, NVD, FIRST EPSS. Last verified by Threadlinqs on 2026-07-12. This product uses the NVD API but is not endorsed or certified by the NVD.

**Vendor advisory and patch**

- [github.com](https://github.com/CoreWCF/CoreWCF/security/advisories/GHSA-48pq-2xq3-c2m4)

**Other references**

- [github.com](https://github.com/CoreWCF/CoreWCF/commit/6a99df3242f54acd6f89edfd6050430b72d0c685)
- [github.com (86dd3232b6b8aaf32281be9e8d798afad6145d58)](https://github.com/CoreWCF/CoreWCF/commit/86dd3232b6b8aaf32281be9e8d798afad6145d58)
- [github.com (9eb9b46d1c2af06fb71f656a02f4d5b4649c1f03)](https://github.com/CoreWCF/CoreWCF/commit/9eb9b46d1c2af06fb71f656a02f4d5b4649c1f03)
- [github.com (v1.8)](https://github.com/CoreWCF/CoreWCF/releases/tag/v1.8.1)
- [github.com (v1.9)](https://github.com/CoreWCF/CoreWCF/releases/tag/v1.9.1)

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-54781
Full detection coverage and IOCs for threats exploiting CVE-2026-54781 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp