CVE-2026-33544 Tinyauth has OAuth account confusion via shared mutable state on singleton service instances
Concurrent OAuth logins can cause identity confusion, allowing one user to gain access to another user's account due to shared mutable state.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-33544?
CVE-2026-33544 is a high-severity vulnerability in steveiliop56 tinyauth, published on 2 Apr 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Official description
Tinyauth is an authentication and authorization server. Prior to version 5.0.5, all three OAuth service implementations (GenericOAuthService, GithubOAuthService, GoogleOAuthService) store PKCE verifiers and access tokens as mutable struct fields on singleton instances shared across all concurrent requests. When two users initiate OAuth login for the same provider concurrently, a race condition between VerifyCode() and Userinfo() causes one user to receive a session with the other user's identity. This issue has been patched in version 5.0.5.
Weakness: CWE-362
Which versions are affected by CVE-2026-33544?
3 open source packages ship an affected version, including github.com/steveiliop56/tinyauth. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
github.com/steveiliop56/tinyauth Go | All versions | 1.0.1-0.20260401140714-fc1d4f2082a5 |
github.com/steveiliop56/tinyauth Go | All versions | 1.0.1-0.20260401140714-fc1d4f2082a5 |
github.com/steveiliop56/tinyauth Go | All versions | 1.0.1-0.20260401140714-fc1d4f2082a5 |
Products include Tinyauth Tinyauth.
How do I fix CVE-2026-33544?
Upgrade github.com/steveiliop56/tinyauth to 1.0.1-0.20260401140714-fc1d4f2082a5 or later.
Is CVE-2026-33544 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-33544 exists.
Other vulnerabilities in steveiliop56 tinyauth
Sources
Also known as GHSA-9q5m-jfc4-wc92, GO-2026-5296.