CoreWCF: SAML SubjectConfirmation methods and holder-of-key proof keys are not enforced

Exploitation

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

CVSS

7.4 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

EPSS

• CVE-2026-54781: 0.25% estimated exploitation activity in the next 30 days; percentile 16.16 (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 The relying application is given a ClaimsPrincipal for a subject whose authority over the assertion the sender never proved. There are two distinct exploit shapes: - Holder-of-key downgrade. An attacker who obtains a holder-of-key SAML assertion that was issued without KeyInfo (issuer bug, custom STS shape, or assertion captured from an interaction where KeyInfo was elided) can present it to the service and be authenticated as the assertion’s subject without producing the proof key the assertion’s confirmation method would normally require. The service’s reliance on holder-of-key for sensitive actions is bypassed. - Custom-method bypass. An attacker who can obtain or arrange the issuance of a SAML assertion bearing a non-standard confirmation method URI (a permissive STS that accepts arbitrary method strings, an experimental custom IDP, or an attacker-side construction that the issuer signs without validating the method field) can present the assertion and be authenticated.…

Published by the source

19 Jun 2026, 20:47 UTC

Last modified by the source

19 Jun 2026, 20:47 UTC

Source last checked

26 Oct 2026, 17:04 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-48pq-2xq3-c2m4

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# Patch Next advisory brief: CVE-2026-54781

Advisory: CoreWCF: SAML SubjectConfirmation methods and holder-of-key proof keys are not enforced
IDs: CVE-2026-54781, GHSA-48pq-2xq3-c2m4
Record: https://patchnext.com/advisories/cve-2026-54781 (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: High (CVSS 7.4)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: corewcf.primitives 1.9.1, 1.8.1. A vendor fix does not mean a deployment is fixed.

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

## Suggested inspection (read-only)
- NuGet corewcf.primitives: 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.primitives.
- 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-48pq-2xq3-c2m4 (GitHub-reviewed advisory GHSA-48pq-2xq3-c2m4 lists affected ranges: NuGet corewcf.primitives >=0 =1.9.0 <1.9.1)

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