Summary
Duende.AccessTokenManagement race condition when concurrently retrieving customized Client Credentials Access Tokens
Duende.AccessTokenManagement contains a race condition when requesting access tokens using the client credentials flow. Concurrent requests to obtain an access token using differing protocol parameters can return access tokens obtained with the wrong scope, resource indicator, or other protocol parameters. Such usage is somewhat atypical, and only a small percentage of users are likely to be affected.
Details
Duende.AccessTokenManagement can request access tokens using the client credentials flow in several ways. In basic usage, the client credentials flow is configured once and the parameters do not vary. In more advanced situations, requests with varying protocol parameters may be made by calling specific overloads of these methods:
HttpContext.GetClientAccessTokenAsync()IClientCredentialsTokenManagementService.GetAccessTokenAsync()
There are overloads of both of these methods that accept a TokenRequestParameters object that customizes token request parameters. However, concurrent requests with varying TokenRequestParameters will result in the same token for all concurrent calls.
Upgrading
Most users can simply update the NuGet package to the latest version. Customizations of the IClientCredentialsTokenCache that derive from the default implementation (DistributedClientCredentialsTokenCache) will require a small code change, as its constructor was changed to add a dependency on the ITokenRequestSynchronization service. The synchronization service will need to be injected into the derived class and passed to the base constructor.
Impact
The impact of this vulnerability depends on how Duende.AccessTokenManagement is used and on the security architecture of the solution. Most users will not be vulnerable to this issue. More advanced users may run into this issue by calling the methods specified above with customized token request parameters. The impact of obtaining an access token with different than intended protocol parameters will vary depending on application logic, security architecture, and the authorization policy of the resource servers.
Thank you to Michael Dimoudis of PageUp for finding this issue and responsibly disclosing it!
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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Frequently Asked Questions
- What is CVE-2025-26620? CVE-2025-26620 is a medium-severity security vulnerability in Duende.AccessTokenManagement (nuget), affecting versions < 3.2.0. It is fixed in 3.2.0.
- Which versions of Duende.AccessTokenManagement are affected by CVE-2025-26620? Duende.AccessTokenManagement (nuget) versions < 3.2.0 is affected.
- Is there a fix for CVE-2025-26620? Yes. CVE-2025-26620 is fixed in 3.2.0. Upgrade to this version or later.
- Is CVE-2025-26620 exploitable, and should I be worried? Whether CVE-2025-26620 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2025-26620 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2025-26620? Upgrade
Duende.AccessTokenManagementto 3.2.0 or later.