Affected: Bitnami: rclone

rclone is a command-line program to sync files and directories to and from different cloud storage providers. Prior to 1.75.0, the shared HTTP CONNECT helper in lib/proxy/http.go parses proxy CONNECT responses with http.ReadResponse over an unrestricted buffered reader, allowing a malicious or compromised configured proxy, or an active on-path actor controlling a plaintext HTTP proxy hop, to send oversized headers that grow memory until the rclone process fails. The affected helper is used by FTP and SFTP proxy connections, and SFTP reaches the parser before SSH server authentication, so target host key validation does not constrain a malicious proxy. This issue is fixed in 1.75.0.

rclone is a command-line program to sync files and directories to and from different cloud storage providers. Prior to 1.75.0, the shared HTTP CONNECT helper in lib/proxy/http.go parses proxy CONNECT responses with http.ReadResponse over an unrestricted buffered reader, allowing a malicious or compromised configured proxy, or an active on-path actor controlling a plaintext HTTP proxy hop, to send oversized headers that grow memory until the rclone process fails. The affected helper is used by FTP and SFTP proxy connections, and SFTP reaches the parser before SSH server authentication, so target host key validation does not constrain a malicious proxy. This issue is fixed in 1.75.0.

Affected: Go: github.com/rclone/rclone

## 1. Summary

The shared HTTP CONNECT helper parses a proxy response with `http.ReadResponse` over an unrestricted buffered reader. The production helper accepted a valid response containing a 2 MiB header in three consecutive runs. A malicious or compromised configured proxy, or an active on-path actor controlling a plaintext HTTP-proxy hop, can grow memory until the process fails.

The security impact is process-wide exhaustion, not loss of access through the malicious proxy, which the proxy already controls. The victim must configure and use the proxy, so UI is Required and the rating is Medium.

## 2. Affected Assets & Attack Surface

- Verified rclone revision: `a0c09f1381ae93e2a9a33c529d170186c61ad058` (`v1.74.0-240-ga0c09f138`) - Current-master check: `lib/proxy/http.go` was unchanged at master commit `961266888fe797390c535386f3b3aa46f4853602` on 2026-07-18 - Shared helper: `lib/proxy/http.go:23-81` - SFTP use: `backend/sftp/ssh_internal.go:25-45` - FTP use: `backend/ftp/ftp.go:465-479` - Proxy peer: configured malicious/compromised proxy or active on-path actor for a plaintext HTTP proxy - TLS boundary: HTTPS proxy connections authenticate the proxy before this response is parsed, so an on-path actor must also defeat TLS

## 3. Technical Root Cause Analysis

`HTTPConnectDial` invokes `http.ReadResponse(br, req)` directly. This call does not inherit `http.Transport.MaxResponseHeaderBytes`. In the Go implementation used for validation, exported `textproto.Reader.ReadM…

Affected: Ubuntu:18.04:LTS: rclone, Ubuntu:Pro:20.04:LTS: rclone, Ubuntu:Pro:22.04:LTS: rclone, Ubuntu:Pro:24.04:LTS: rclone, Ubuntu:Pro:26.04:LTS: rclone

rclone is a command-line program to sync files and directories to and from different cloud storage providers. Prior to 1.75.0, the shared HTTP CONNECT helper in lib/proxy/http.go parses proxy CONNECT responses with http.ReadResponse over an unrestricted buffered reader, allowing a malicious or compromised configured proxy, or an active on-path actor controlling a plaintext HTTP proxy hop, to send oversized headers that grow memory until the rclone process fails. The affected helper is used by FTP and SFTP proxy connections, and SFTP reaches the parser before SSH server authentication, so target host key validation does not constrain a malicious proxy. This issue is fixed in 1.75.0.

Ein Angreifer kann mehrere Schwachstellen in rclone ausnutzen, um beliebigen Programmcode auszuführen, um einen Denial of Service Angriff durchzuführen, um Informationen offenzulegen, um Dateien zu manipulieren, und um Sicherheitsvorkehrungen zu umgehen.