rclone before 1.74.4 Privilege Escalation via setuid Metadata

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

rclone before 1.74.4 fails to mask special permission bits when applying source-supplied mode metadata in the local backend, allowing attackers to set setuid/setgid bits on attacker-controlled files. When copying with metadata preservation from an untrusted remote, attackers can plant a setuid binary that escalates privileges to root if rclone runs as root, or to the service account user otherwise.

Source published

25 Aug 2026 15:16:11 UTC

Source modified

25 Aug 2026 16:11:49 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · 2.0 CVSS:4.0/AV:L/AC:H/AT:P/PR:N/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N

CVSS 3.1 · 3.6 CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:N

rclone before 1.74.4 fails to mask special permission bits when applying source-supplied mode metadata in the local backend, allowing attackers to set setuid/setgid bits on attacker-controlled files. When copying with metadata preservation from an untrusted remote, attackers can plant a setuid binary that escalates privileges to root if rclone runs as root, or to the service account user otherwise.

Source published

Aug 25, 2026, 3:16:11 PM (timezone not stated)

Source modified

Aug 25, 2026, 4:11:49 PM (timezone not stated)

Observed here

11 Nov 2026 16:10:01 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 4.0 · 2.0 CVSS:4.0/AV:L/AC:H/AT:P/PR:N/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N

rclone before 1.74.4 fails to mask special permission bits when applying source-supplied mode metadata in the local backend, allowing attackers to set setuid/setgid bits on attacker-controlled files. When copying with metadata preservation from an untrusted remote, attackers can plant a setuid binary that escalates privileges to root if rclone runs as root, or to the service account user otherwise.

Source published

25 Aug 2026 16:17:30 UTC

Source modified

10 Sep 2026 20:46:19 UTC

Observed here

25 Oct 2026 16:19:10 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · [email protected] · Secondary · 2.0 CVSS:4.0/AV:L/AC:H/AT:P/PR:N/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

CVSS 3.1 · [email protected] · Secondary · 3.6 CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:N

### Summary When writing an object with metadata, the local backend applies the source-supplied `mode`, `uid`, and `gid` verbatim: it parses `mode` as an octal integer and passes it straight into `os.Chmod(o.path, os.FileMode(umode))`, and passes `uid`/`gid` straight into `os.Chown`. The value is never masked to permission bits, so any value with Go's `ModeSetuid` (1<<23) or `ModeSetgid` (1<<22) bit set causes the setuid/setgid bit to be applied. Because both the file content and its metadata come from the (attacker-controlled) source remote, an attacker stores a binary of their choosing with `mode = 40000755` (and `uid = 0`); when the victim runs `rclone copy -M <remote>: /dest`, rclone writes the attacker's binary and makes it setuid. If the victim runs rclone as root (typical for system backup/restore), the `uid=0` chown plus setuid produces a root-owned setuid binary with attacker content — any local user then escalates to root. When rclone runs as a non-root service user, the planted setuid binary is owned by that user, giving any local user that user's privileges (lateral escalation / persistent backdoor). ### Details `backend/local/metadata.go`, `writeMetadataToFile()`: ```go uid, hasUID := o.parseMetadataInt(m, "uid", 10) gid, hasGID := o.parseMetadataInt(m, "gid", 10) if hasUID { ... err = os.Chown(o.path, uid, gid) // source-controlled owner, no same-uid guard } mode, hasMode := o.parseMetadataInt(m, "mode", 8) if hasMode && mode >= 0 { umode := uint(mode) if umode <= math.MaxUint32 { err = os.Chmod(o.path, os.FileMode(umode)) // <-- raw value; ModeSetuid/ModeSetgid NOT masked off } } ``` `os.Chmod`/`os.FileMode` honor `ModeSetuid`/`ModeSetgid`/`ModeSticky`. There is no `&^ (os.ModeSetuid|os.ModeSetgid)` mask and no check that the source is trusted, so an attacker-chosen `mode` string sets those bits on the freshly written, attacker-controlled file. (Note: a legitimate local source reports `mode` in unix `st_mode` layout e.g. `0106755`, whose bit 1<<23 is unset, so honest copies happen to drop setuid — but the attacker supplies the Go-`FileMode` layout `40000755` directly, which sets it.) ### PoC 1) Get the official stable binary: ``` curl -fsSLO https://downloads.rclone.org/v1.74.3/rclone-v1.74.3-linux-amd64.zip unzip -j rclone-v1.74.3-linux-amd64.zip '*/rclone' -d . # ./rclone -> v1.74.3 ``` 2) Create a payload (the attacker-controlled binary content) and copy it with the malicious `mode` metadata: ``` mkdir -p msrc mdst && cp /bin/true msrc/payload ./rclone copy -M --metadata-set mode=40000755 msrc mdst # 40000755 = Go FileMode setuid|0755 ``` 3) Observe — the destination file is now setuid: ``` stat -c '%A %a' mdst/payload -rwsr-xr-x 4755 # 's' = setuid bit SET on attacker binary ``` Variants: `mode=20000755` → setgid (`-rwxr-sr-x`); `mode=60000755` → both (`-rwsr-sr-x`). With rclone run as root and the source object also carrying `uid=0`/`gid=0`, the file is chown'd root:root, yielding a root-owned setuid binary executable by any local user. ### Impact A victim performing a metadata-preserving copy/restore (`-M`) from an untrusted or compromised remote installs an attacker-chosen executable with the setuid/setgid bit set. Run as root (system backup/restore, the common case for `--metadata`), this is a root-owned setuid root backdoor executable by any local user → local privilege escalation to root. Run as a non-root user, it is a setuid backdoor for that service account. The companion `uid`/`gid` application lets a root-run transfer also reassign ownership of written files arbitrarily. ### Remediation Mask special bits before applying mode from metadata — `os.Chmod(o.path, os.FileMode(umode).Perm())` (or `umode & 0o777`) — and do not honor setuid/setgid/sticky from source metadata; gate `uid`/`gid`/setuid application behind an explicit opt-in (e.g. `--local-metadata-set-ownership`) that is off by default, and document that `-M` from untrusted remotes must not restore privileged bits. Regression test: copying an object with `mode=40000755`/`uid=0` must produce a non-setuid, caller-owned file unless the opt-in is set.

Source published

5 Aug 2026 20:03:14 UTC

Source modified

25 Sep 2026 14:25:48 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:N

Publisher rating · LOW

Unsafe file permission restoration from metadata in github.com/rclone/rclone

Source published

18 Aug 2026 16:38:10 UTC

Source modified

25 Sep 2026 14:25:48 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

OSV · upstream source license applies

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · OSV · upstream source license applies. Source text is retained; field grouping and change labels are provided by ChangeIntel.