CVE-2026-88045

rclone 1.75.0 contains a memory-allocation flaw (CWE-789) in the streamed multipart path of its `rclone serve s3` server: an attacker-controlled Content-Length or X-Amz-Decoded-Content-Length is passed to multipart.NewRW().Reserve before any body bytes are read, and the waitForTurn logic admits the current part plus one oversized part even when this exceeds the configured --multipart-streaming-buffer-limit, with the lib/pool allocator backing reservations in 1 MiB pages. A network client can therefore declare large multipart uploads and never send the declared bodies, retaining or multiplying memory reservations. The attacker gains remote denial of service - process or host memory exhaustion or permanently blocked request handlers - with no confidentiality or integrity impact (CVSS 3.1: 7.5, availability only). Anyone running `rclone serve s3` on an affected version is exposed: anonymous S3 deployments need no credentials, while deployments with auth_key require an accepted S3 key. There is no known exploitation, public proof-of-concept, or CISA KEV listing, and the flaw is fixed in rclone 1.75.1.

What to do: Upgrade to rclone 1.75.1. If immediate upgrade is not possible, restrict access to `rclone serve s3` endpoints to trusted networks, require an auth_key so anonymous clients cannot trigger the condition, and monitor process/host memory and hung request handlers. Inventory your estate for deployments running rclone 1.75.0 with the S3 server enabled, prioritizing anonymous (unauthenticated) deployments.