# CVE-2026-54779: CoreWCF SAML token replay protection bypass in DefaultTokenReplayCache

Source: https://junglewise.ai/threats/cve-2026-54779-corewcf-saml-token-replay-protection-bypass-in  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-08. Updated: 2026-07-08  
License: CC BY 4.0 with a link back

CVE-2026-54779 · Severity: medium · CVSS 5.9 · Published 2026-07-08

CoreWCF, a library used to build web services on .NET Core, contains a flaw where security tokens can be reused by an attacker. Although the software has a setting to prevent 'replay attacks,' a bug in the underlying code fails to actually block duplicate tokens. This could allow an unauthorized user to capture a legitimate login token and reuse it to gain access to the service.

Technologies: [CoreWCF](https://junglewise.ai/threats/technologies/corewcf), [CoreWCF.Primitives (NuGet)](https://junglewise.ai/threats/technologies/corewcf-primitives). Vendors: [CoreWCF](https://junglewise.ai/threats/vendors/corewcf), [NuGet](https://junglewise.ai/threats/vendors/nuget).

## Quick answers

**Is CVE-2026-54779 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-54779 being exploited in the wild.

**How severe is CVE-2026-54779?** Medium severity, with a CVSS score of 5.9, published 8 July 2026.

**Which products and versions are affected?** CoreWCF < 1.8.1, >= 1.9.0 < 1.9.1; CoreWCF.Primitives (NuGet) ECOSYSTEM:introduced=0,fixed=1.8.1.

**Is there a fix for CVE-2026-54779?** Yes. CoreWCF.Primitives (NuGet): upgrade to 1.8.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-54779 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-54779?** Check whether you run CoreWCF or CoreWCF.Primitives (NuGet) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- CoreWCF.Primitives (NuGet): upgrade to 1.8.1 or later

  ```sh
  dotnet add package CoreWCF.Primitives --version 1.8.1
  ```


## Technical details

A vulnerability exists in CoreWCF's SAML token validation logic where the 'DetectReplayedTokens' setting is ineffective. The root cause is in the 'DefaultTokenReplayCache.TryAdd' implementation, which unconditionally returns true even if a token key is already present in the cache. This bypasses the replay check performed by the inner Microsoft.IdentityModel.Tokens.Saml handler. An attacker who captures a valid SAML token can successfully replay it against the service to gain unauthorized access. The fix replaces the MemoryCache backing with a ConcurrentDictionary and ensures 'TryAdd' correctly identifies and rejects existing keys. This issue is resolved in versions 1.8.1 and 1.9.1.

## Affected products

- CoreWCF CoreWCF < 1.8.1, >= 1.9.0 < 1.9.1

## Identifiers

- CVE-2026-54779
- GHSA-9jr3-rj99-8jq3

## Timeline

- 2026-07-08: disclosed
- 2026-07-08: advisory

## References

- [https://github.com/CoreWCF/CoreWCF/commit/3800c4e2bb4c6fde00ddacefdc2221ef33d55621](https://github.com/CoreWCF/CoreWCF/commit/3800c4e2bb4c6fde00ddacefdc2221ef33d55621)
- [https://github.com/CoreWCF/CoreWCF/commit/7b0b5231cf21b4b5c1fc3caac9981f8bee43823f](https://github.com/CoreWCF/CoreWCF/commit/7b0b5231cf21b4b5c1fc3caac9981f8bee43823f)
- [https://github.com/CoreWCF/CoreWCF/commit/84f8cff5a786b5aaa73448cb379d366a7df98238](https://github.com/CoreWCF/CoreWCF/commit/84f8cff5a786b5aaa73448cb379d366a7df98238)
- [https://github.com/CoreWCF/CoreWCF/releases/tag/v1.8.1](https://github.com/CoreWCF/CoreWCF/releases/tag/v1.8.1)
- [https://github.com/CoreWCF/CoreWCF/releases/tag/v1.9.1](https://github.com/CoreWCF/CoreWCF/releases/tag/v1.9.1)
- [https://github.com/CoreWCF/CoreWCF/security/advisories/GHSA-9jr3-rj99-8jq3](https://github.com/CoreWCF/CoreWCF/security/advisories/GHSA-9jr3-rj99-8jq3)

## Related threats

- [CoreWCF cleartext proof key exposure in SPNEGO negotiation](https://junglewise.ai/threats/cve-2026-54784-corewcf-cleartext-proof-key-exposure-in-spnego-negotiation)
- [CoreWCF signature verification bypass in WS-Security](https://junglewise.ai/threats/cve-2026-54783-corewcf-signature-verification-bypass-in-ws-security)
- [CoreWCF authentication bypass in SAML token validation](https://junglewise.ai/threats/cve-2026-54782-corewcf-authentication-bypass-in-saml-token-validation)
- [CoreWCF improper authentication in SAML SamlSecurityTokenHandler](https://junglewise.ai/threats/cve-2026-54781-corewcf-improper-authentication-in-saml-samlsecuritytokenhandler)
- [CoreWCF algorithm downgrade in WS-Security receive pipeline](https://junglewise.ai/threats/cve-2026-54780-corewcf-algorithm-downgrade-in-ws-security-receive-pipeline)