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.
The product deserializes untrusted data without sufficiently ensuring that the resulting data will be valid.
| Link | Tags |
|---|---|
| https://github.com/LLK/scratch-vm/pull/2476 | third party advisory |
| https://scratch.mit.edu/discuss/topic/422904/?page=1#post-4223443 | vendor advisory |