CVE-2026-63462

## Summary An unauthenticated `POST` to any OpenAPI-validated endpoint, including the anonymous `POST /edge/validate` and `POST /edge/issue-token`, crashes the entire Unleash server with one request body of deeply-nested JSON. When request-body validation fails, Unleash builds the error message by calling `JSON.stringify` on the raw offending value taken from the request body. A value nested a few thousand levels deep makes `JSON.stringify` recurse past the V8 call-stack limit and throw `RangeError: Maximum call stack size exceeded`. The throw is synchronous inside an Express error-handling middleware that has no try/catch, and the process registers no `uncaughtException` handler (only `unhandledRejection`). Node terminates the process with `exit(1)`. The body parser sets no JSON nesting-depth limit, the payload (about 10 KB at depth 5000) stays far under the 100 KB body-size limit, and the same error formatter serves every API route, so the trigger is route-independent. Result: a remote attacker with no account, token, or cookie takes the whole server offline with a single 10 KB request, and keeps it offline by replaying it. ## Affected Unleash OSS server, confirmed live-exploitable on v8.0.0 (`unleashorg/unleash-server:8.0.0`). Vulnerable code is the shared request-validation error path (`src/lib/error/bad-data-error.ts` `genericErrorMessage`), present on current `main`. Reachable on a stock install: no feature flag, no setting, no authentication, no CSRF token, and no cookie required. The 100 KB request-body size limit does not mitigate it; the crashing payload is about 10 KB. ## Root cause On validation failure the error formatter serializes the raw offending request value with an unguarded `const youSent = JSON.stringify(propertyValue)` (`src/lib/error/bad-data-error.ts:75`), where `propertyValue` is read straight from the request body via `lodash.get` (`bad-data-error.ts:123`). A deeply-nested array or object makes `JSON.stringify` recurse once per le