CVE-2026-79783: rclone Privilege Escalation Vulnerability

CVE-2026-79783 Overview

CVE-2026-79783 is a local privilege escalation vulnerability in rclone versions before 1.74.4. The local backend fails to mask special permission bits when applying source-supplied mode metadata during file transfers. Attackers can set setuid and setgid bits on attacker-controlled files copied from an untrusted remote. When rclone runs as root with metadata preservation enabled, a planted setuid binary escalates privileges to root. If rclone runs as a service account, the binary escalates to that account. The vulnerability is classified as CWE-732: Incorrect Permission Assignment for Critical Resource.

Critical Impact
Attackers controlling a remote source can plant setuid binaries on the local filesystem, escalating privileges to the user rclone runs as, including root.

Affected Products

rclone versions prior to 1.74.4
Deployments using the local backend with metadata preservation flags
Systems executing rclone as root or a privileged service account

Discovery Timeline

2026-08-25 - CVE-2026-79783 published to the National Vulnerability Database (NVD)
2026-08-25 - Last updated in NVD database

Technical Details for CVE-2026-79783

Vulnerability Analysis

rclone supports preserving Unix file mode metadata when copying between backends. When the local backend applies mode bits supplied by a source, it does not mask the special permission bits S_ISUID (setuid), S_ISGID (setgid), or the sticky bit. An attacker controlling a remote or archive source can specify a mode value such as 04755 for an executable file. On copy, rclone writes this mode directly to the destination file without sanitization.

The result is a functional setuid binary owned by the user account executing rclone. Any local user who executes the binary inherits the effective UID of that account. When rclone is invoked from cron, backup scripts, or container entrypoints as root, this yields full root privileges on the host.

Root Cause

The defect is a missing permission mask in the local backend metadata application logic. Standard practice for tools handling untrusted archives is to strip special bits using a mask such as mode & 0777. rclone omitted this mask when the --metadata or equivalent preservation flag was active, treating source-supplied mode values as trusted.

Attack Vector

Exploitation requires local access to trigger rclone execution and control over a source rclone reads from. The attacker stages a payload binary at an untrusted remote or shared storage location and marks its mode metadata with setuid or setgid bits. When an administrator or automation runs rclone copy with metadata preservation into a locally accessible directory, the binary lands with special bits intact. The attacker then executes the binary to gain the target user identity.

Refer to the GitHub Security Advisory GHSA-945v-v9p3-v5xw and the VulnCheck Privilege Escalation Advisory for additional context.

Detection Methods for CVE-2026-79783

Indicators of Compromise

Files under rclone destination directories with setuid or setgid bits set, discoverable via find <path> -perm /6000 -type f
rclone process invocations using --metadata, --metadata-mapper, or backend-specific metadata preservation flags against untrusted remotes
Recently created executables owned by root or service accounts in world-writable or user-writable paths
Unexpected changes to stat mode values on binaries following scheduled rclone jobs

Detection Strategies

Audit rclone versions across the fleet and flag hosts running versions earlier than 1.74.4
Monitor filesystem events for chmod operations setting bits 04000 or 02000 initiated by the rclone process
Alert on new setuid binaries appearing outside of package manager transactions using auditd rules on chmod, fchmod, and fchmodat syscalls

Monitoring Recommendations

Ingest EDR process telemetry for rclone command lines and correlate with subsequent setuid file creation events
Baseline the inventory of setuid binaries per host and alert on additions
Log rclone job configurations from cron, systemd timers, and CI pipelines to identify metadata preservation use against external remotes

How to Mitigate CVE-2026-79783

Immediate Actions Required

Upgrade rclone to version 1.74.4 or later on all hosts and container images
Identify running rclone jobs executing as root and reduce privileges to a dedicated unprivileged account where feasible
Scan destination directories for existing setuid or setgid files and remove any that were not intentionally installed

Patch Information

The fix is included in rclone 1.74.4. The upstream patch masks special permission bits when applying source-supplied mode metadata in the local backend. Release notes and commit details are available in the GitHub Security Advisory GHSA-945v-v9p3-v5xw.

Workarounds

Disable metadata preservation by omitting --metadata and --metadata-mapper flags when copying from untrusted sources
Run rclone under an unprivileged user account isolated from sensitive paths and binaries
Mount destination filesystems with the nosuid option to neutralize setuid bits on files written to those volumes

bash

# Mount destination volume with nosuid to block setuid execution
mount -o remount,nosuid /var/rclone/dest

# Verify no unexpected setuid or setgid files exist under rclone targets
find /var/rclone/dest -perm /6000 -type f -ls

# Confirm patched version is installed
rclone version | head -n1