# CVE-2026-77763: JuiceFS Local Filestore Backend Joins Object Keys onto the Storage Root Without a Containment Check, Allowing Writes Outside the Configured Directory

Status: published. Published: 2026-08-21. Updated: 2026-11-08.

The filestore backend in pkg/object/file.go, used for file:// stores and as a common juicefs sync destination, derived every operation's target from path(key), which returned either filepath.Join(d.root, key) or filepath.Clean(d.root + key) with no check that the result stayed beneath the root. Put, Get, Head, Delete, Chmod, Chown, Symlink and Readlink all consumed that value directly. Object keys enumerated from a source object store during a sync are not constrained the way local filesystem names are, so a key containing traversal segments causes juicefs to write attacker-supplied content to a path outside the intended local destination, and no error is returned. An operator syncing from a bucket whose contents they do not fully control, such as a shared or public bucket or one an attacker can write to, is therefore exposed to a file write at an attacker-influenced location. The fix changes path() to return an error and rejects any key whose resolved path escapes the root.

## Remediation

- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: VulnCheck) — https://github.com/juicedata/juicefs/commit/0bcd70b3d13088d38127d6fb5750c91be7c4ec16
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: VulnCheck) — https://github.com/juicedata/juicefs/pull/7425

## Affected products and versions

- juicedata / juicefs (github.com/juicedata/juicefs): ≥ 0; ≤ 1.4.1 (affected, semver). Source: CNA: VulnCheck

## Severity and prioritization

- CVSS 3.1: 6.5 (medium); CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N; source: CNA: VulnCheck

- CVSS 4.0: 7.1 (high); CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N; source: CNA: VulnCheck

- CISA KEV: No listing in collected sources

- EPSS: 0.50% as of 2026-11-08; percentile 42.94%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-22

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/juicedata/juicefs/issues/7401 (CNA: VulnCheck; issue-tracking)

- https://github.com/juicedata/juicefs/commit/0bcd70b3d13088d38127d6fb5750c91be7c4ec16 (CNA: VulnCheck; patch)

- https://github.com/juicedata/juicefs/pull/7425 (CNA: VulnCheck; issue-tracking, patch)

- https://github.com/juicedata/juicefs/blob/v1.4.1/pkg/object/file.go (CNA: VulnCheck; technical-description)

- https://github.com/juicedata/juicefs (CNA: VulnCheck; product)

- https://www.vulncheck.com/advisories/juicefs-local-filestore-backend-joins-object-keys-onto-the-storage-root-without-a-containment-check-allowing-writes-outside-the-configured-directory (CNA: VulnCheck; third-party-advisory)

## Provenance

- CNA: VulnCheck: https://www.cve.org/CVERecord?id=CVE-2026-77763; retrieved 2026-11-08; source updated 2026-11-08

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-77763; retrieved 2026-11-08; source updated Not reported

Revision: 15f52e682749763811411ee295b6cb7d15df56b46b23589cb866a99ffc8862eb

Canonical: https://y2.dev/cve/CVE-2026-77763

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