Parse Server is an open source backend that can be deployed to any infrastructure that can run Node.js. Prior to 9.9.1-alpha.12 and 8.6.82, deeply nested $or, $and, and $nor query condition operators in the REST API or LiveQuery query handling could trigger exponential-time processing in the internal query-traversal helper and block the Node.js event loop. This issue is fixed in versions 9.9.1-alpha.12 and 8.6.82.
https://github.com/parse-community/parse-server/security/advisories/GHSA-cgxm-vr2f-6fj8
https://github.com/parse-community/parse-server/releases/tag/9.9.1-alpha.12
https://github.com/parse-community/parse-server/releases/tag/8.6.82
https://github.com/parse-community/parse-server/pull/10512
https://github.com/parse-community/parse-server/pull/10511
https://github.com/parse-community/parse-server/commit/1103c7a890e0455ba3dccd4bc5db17efe1789c9a
https://github.com/parse-community/parse-server/commit/0f5d2ad77b422dc904458254548be87397fc6e9b