Description
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.
Remediation
References
https://github.com/LLK/scratch-vm/pull/2476
https://scratch.mit.edu/discuss/topic/422904/?page=1#post-4223443
Related Vulnerabilities
CVE-2015-6420 Vulnerability in maven package commons-collections:commons-collections
CVE-2020-1938 Vulnerability in maven package org.apache.tomcat:tomcat-util
CVE-2016-10546 Vulnerability in npm package pouchdb
CVE-2020-8205 Vulnerability in npm package @uppy/companion
CVE-2017-5878 Vulnerability in maven package org.red5:red5-server