Weakness Type (CWE)

CWE-863 — CWE-863 Incorrect Authorization

CAPEC

CVSS 4.0 Score

7

HIGH

CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:H/VA:L/SC:N/SI:H/SA:N

Vulnerability 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.

Affected

pkg:github/hexpm/hexpm

Module Source File Routine
HexpmWeb.API.OAuthController lib/hexpm_web/controllers/api/oauth_controller.ex HexpmWeb.API.OAuthController.validate_scopes_against_key/2
Status Type Version Changes / Fixed in
affected git ⓘ 71829cb6f655 < 71c127afebb7

hexpm / hex.pm

Status Type Version Changes / Fixed in
affected date 2025-08-18 < 2026-03-05

Workarounds

  • Revoke and reissue exposed API keys immediately if compromise is suspected.
  • Avoid relying on read-only API keys as a strict security boundary in high-risk environments.
  • Closely monitor audit logs for unexpected API key creation events.
  • Enforce strong 2FA hygiene and protect TOTP seeds carefully.

There is no complete mitigation without upgrading, as the issue exists in server-side scope validation logic.

References

Credits

  • Finder: Michael Lubas / Paraxial.io
  • Remediation developer: Jonatan Männchen / EEF

CVE record as JSON:  GET /cves/CVE-2026-21621.json
OSV record as JSON:  GET /osv/EEF-CVE-2026-21621.json