# CVE-2026-75866: Punk::OAuth2::Server versions through 0.03 for Perl issue access tokens outside a client's registered scopes and grant types because no auth

> Attackers can obtain access tokens with unauthorized scopes or grant types, bypassing OAuth2 authorization checks in Punk::OAuth2::Server.

- **Severity:** Critical 9.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 22 Aug 2026
- **Updated:** 25 Aug 2026
- **Also known as:** GHSA-cjjx-w599-qf62

## What is CVE-2026-75866?

CVE-2026-75866 is a critical missing authorization vulnerability, published on 22 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Punk::OAuth2::Server versions through 0.03 for Perl issue access tokens outside a client's registered scopes and grant types because no authorization path reads them.

Punk::OAuth2::Server::Store registers scopes and grant_types per client and documents both as client registration. token dispatches on the grant_type in the request body, so a client registered for authorization_code alone can ask for client_credentials, and that arm passes the requested scope straight to the minter, which signs it into the at+jwt access token. authorize copies the query scope into the authorization code record without comparing it against the registration, leaving the optional consent hook as the only check between an arbitrary scope and the issued code. redirect_uris on the same client row is read and enforced.

A registered client can obtain a correctly signed token carrying any scope it names, and a resource server running Punk::OAuth2::Checker accepts that token and honours the scope. A client registered without a secret authenticates on its client_id alone, so anyone who knows that identifier can request one.

Weakness: CWE-862 (Missing Authorization)

## Which versions are affected by CVE-2026-75866?


## How do I fix CVE-2026-75866?

No fix has been published for CVE-2026-75866 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-75866 being exploited?

There is no known exploitation of CVE-2026-75866 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-75866 and fix it if it is affected.

What it is: CVE-2026-75866 is a critical missing authorization vulnerability, published on 22 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-75866 in the wild and no public exploit code.

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-2026-75866/ (Markdown: https://insights.sbomify.com/CVE-2026-75866/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-75866
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-75866
- OSV: https://osv.dev/vulnerability/CVE-2026-75866

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-75866/
Summaries are generated and may contain mistakes; the official description above is the record.