# 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.

- **Severity:** High 7.7 (`CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:H/A:N`)
- **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:** Yes
- **Published:** 2 Apr 2026
- **Updated:** 3 Apr 2026
- **Also known as:** GHSA-9q5m-jfc4-wc92, GO-2026-5296

## 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 (Concurrent Execution using Shared Resource with Improper Synchronization)

## 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 | Ecosystem | 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: 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

- [CVE-2026-32246](https://insights.sbomify.com/CVE-2026-32246/): Tinyauth vulnerable to TOTP/2FA bypass via OIDC authorize endpoint (high 8.5)
- [CVE-2026-32245](https://insights.sbomify.com/CVE-2026-32245/): Tinyauth's OIDC authorization codes are not bound to client on token exchange (medium 6.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-33544 and fix it if it is affected.

What it is: 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.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-33544 exists.

Affected packages and fixed versions:
- github.com/steveiliop56/tinyauth (Go): affected all versions; fixed in 1.0.1-0.20260401140714-fc1d4f2082a5
- github.com/steveiliop56/tinyauth (Go): affected all versions; fixed in 1.0.1-0.20260401140714-fc1d4f2082a5
- github.com/steveiliop56/tinyauth (Go): affected all versions; fixed in 1.0.1-0.20260401140714-fc1d4f2082a5

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-33544/ (Markdown: https://insights.sbomify.com/CVE-2026-33544/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-33544
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-33544
- OSV: https://osv.dev/vulnerability/CVE-2026-33544

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-33544/
Summaries are generated and may contain mistakes; the official description above is the record.