CVE-2026-47138

Parse Server: Pre-authentication denial of service via client version header regex backtracking

### Impact An unauthenticated attacker who knows a publicly-known Parse Application ID can submit a single HTTP request whose client SDK version field contains adversarial input that triggers polynomial backtracking in a request-header parser. The parsing runs before session authentication and before rate limiting on every `/parse/*` request, so the request consumes seconds to minutes of synchronous CPU on a Node.js worker before any access control evaluates it. A small number of concurrent requests can saturate a worker; a single large request via the body-field variant can pin a worker for minutes. Production deployments running the default configuration are affected. ### Patches The client SDK version capture and parsing have been removed entirely. The Parse JS SDK compatibility table defines a strict version-pinned contract between Parse Server and the Parse JS SDK; server-side adaptation to client SDK version is an obsolete pattern that contradicts that contract. The vulnerable parser, the `clientSDK` parameter that threaded its output through routers, and the legacy code path it gated are all removed. The `X-Parse-Client-Version` header and `_ClientVersion` JSON body field are now silently ignored on every request; supported Parse SDKs are unaffected. ### Workarounds Deploy a reverse proxy or WAF in front of Parse Server that strips or strictly size-limits the `X-Parse-Client-Version` header AND the `_ClientVersion` field in JSON request bodies on every `/parse/*` route before forwarding to the server. A header-size cap alone is insufficient: the body-field variant requires inspection of JSON content. Upgrading to the patched version is the recommended remediation.