CVE-2026-21621 Improper Scope Enforcement in OAuth client_credentials Flow Allows Read-Only API Key to Escalate to Full Access

High 7.0 Published 5 Mar 2026 Updated 6 Apr 2026

Attackers with read-only API keys and 2FA codes can escalate to full write access, allowing package modification or publication.

Exploited in the wild: Not known
Login needed: Any signed-in user
Attackable: Over the internet
Victim action needed: Not needed
Fix: None listed

What is CVE-2026-21621?

CVE-2026-21621 is a high-severity vulnerability in hexpm hex.pm, published on 5 Mar 2026. Any signed-in user can exploit it over the network, with no action from the victim.

Official description

Incorrect Authorization vulnerability in hexpm hexpm/hexpm ('Elixir.HexpmWeb.API.OAuthController' module) allows Privilege Escalation.

An API key created with read-only permissions (domain: "api", resource: "read") can be escalated to full write access under specific conditions.

When exchanging a read-only API key via the OAuth client_credentials grant, the resource qualifier is ignored. The resulting JWT receives the broad "api" scope instead of the expected "api:read" scope. This token is therefore treated as having full API access.

If an attacker is able to obtain a victim's read-only API key and a valid 2FA (TOTP) code for the victim account, they can use the incorrectly scoped JWT to create a new full-access API key with unrestricted API permissions that does not expire by default and can perform write operations such as publishing, retiring, or modifying packages.

This vulnerability is associated with program files lib/hexpm_web/controllers/api/oauth_controller.ex and program routines 'Elixir.HexpmWeb.API.OAuthController':validate_scopes_against_key/2.

This issue affects hexpm: from 71829cb6f6559bcceb1ef4e43a2fb8cdd3af654b before 71c127afebb7ed7cc637eb231b98feb802d62999.

Weakness: CWE-863

Which versions are affected by CVE-2026-21621?

It affects 1 product.

Products include Hex Hexpm.

How do I fix CVE-2026-21621?

No fix has been published for CVE-2026-21621 yet. Limit exposure of the affected software until one is available.

Is CVE-2026-21621 being exploited?

There is no known exploitation of CVE-2026-21621 in the wild and no public exploit code.

Sources

Also known as EEF-CVE-2026-21621, GHSA-739m-8727-j6w3.