CVE intelligence and bounded remediation
CVE-2020-14000 — Mit Scratch-Vm security vulnerability
MIT Lifelong Kindergarten Scratch scratch-vm before 0.2.0-prerelease.20200714185213 loads extension URLs from untrusted project.json files with certain _ characters, resulting in remote code execution because the URL's content is treated as a script and is executed as a worker. The responsible code is getExtensionIdForOpcode in serialization/sb3.js. The use of _ is incompatible with a protection mechanism in older versions, in which URLs were split and consequently deserialization attacks were prevented. NOTE: the scratch.mit.edu hosted service is not affected because of the lack of worker scripts.
- Severity
- Critical
- CVSS
- 9.8 (3.1)
- Published
- 2020-07-16
- CISA KEV
- Not currently listed
- Ecosystem
- software/application
- Weaknesses
- CWE-502
Affected products
- mit / scratch-vm
Matched remediation archetype
Unsafe deserialization and object reconstruction
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Check exposure
- Inventory serialization formats accepted from requests, queues, caches, files, cookies, and cross-service messages.
- Trace whether untrusted input can select classes, types, callbacks, constructors, or object hooks during decoding.
- Identify signing, schema validation, trust-boundary, and compatibility settings for each decoder.
Remediate safely
- Replace native object deserialization with a data-only format and explicit schema validation.
- If replacement is not immediate, use a safe decoder with a minimal type allowlist and disable polymorphic or executable hooks.
- Update the affected library and add inert tests for unknown types, extra fields, malformed nesting, and unsigned data.
Authoritative sources
Complete CVE record and remediation plan
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