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, 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: 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 . This product uses the NVD API but is not endorsed or certified by the NVD.