CVE-2026-107805: Nginx UI: Unauthenticated signed-request body staging can exhaust temporary storage

In Nginx UI versions 2.5.0 through 2.5.x, the node-signature authentication path staged an attacker-controlled request body in a temporary file and synchronized it to disk before validating the body digest and cryptographic signature. An unauthenticated remote client that can reach the API can provide syntactically valid signature metadata and cause storage and I/O consumption before the request is rejected.