CVE intelligence and bounded remediation

CVE-2021-29437 — ScratchOAuth2 is an Oauth implementation for Scratch

High CVSS 8

ScratchOAuth2 is an Oauth implementation for Scratch. Any ScratchOAuth2-related data normally accessible and modifiable by a user can be read and modified by a third party. 1. Scratch user visits 3rd party site. 2. 3rd party site asks user for Scratch username. 3. 3rd party site pretends to be user and gets login code from ScratchOAuth2. 4. 3rd party site gives code to user and instructs them to post it on their profile. 5. User posts code on their profile, not knowing it is a ScratchOAuth2 login code. 6. 3rd party site completes login with ScratchOAuth2. 7. 3rd party site has full access to anything the user could do if they directly logged in. See referenced GitHub security advisory for patch notes and workarounds.

Severity
High
CVSS
8 (3.1)
Published
2021-04-13
CISA KEV
Not currently listed
Ecosystem
software/application
Weaknesses
CWE-863

Affected products

  • scratchoauth2_project / scratchoauth2

Matched remediation archetype

Authorization bypass, IDOR, and cross-tenant access

This catalog composition supplies bounded fallback guidance. Explicitly reviewed curated workflows load with the complete record below.

Check exposure

  • Map object and action authorization checks across API, UI, batch, import/export, and background-job paths.
  • Identify tenant, ownership, role, and policy boundaries for affected resources and administrative operations.
  • Use synthetic fixtures to compare intended access matrices without accessing another user's real data.

Remediate safely

  • Enforce server-side authorization at each resource access and state transition using the authenticated principal and trusted tenant context.
  • Scope data queries by tenant and ownership; treat client-supplied identifiers, roles, and policy claims as untrusted.
  • Add deny-by-default policy tests for horizontal and vertical access across every affected transport.

Authoritative sources

Complete CVE record and remediation plan

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