CVE-2025-26620 — Duende.AccessTokenManagem…
Fix: DuendeSoftware/foss@a33332dCVE-2025-26620 is a CWE-367 vulnerability in Duende.AccessTokenManagement. A fix is available for Duende.AccessTokenManagement — see the affected versions and patch details below.
Duende.AccessTokenManagement race condition when concurrently retrieving customized Client Credentials Access Tokens
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2025-26620.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Real-World Exposure
Duende.AccessTokenManagementReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects NuGet packages — download data is not available via public APIs for these ecosystems.
Description
Summary
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 Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| .NETNuGet | Duende.AccessTokenManagement | all versions | 3.2.0dotnet add package Duende.AccessTokenManagement --version 3.2.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Duende.AccessTokenManagement, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update Duende.AccessTokenManagement to 3.2.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-26620 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2025-26620 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2025-26620. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2025-26620 in your dependencies?
O3 Security finds CVE-2025-26620 across NuGet dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.