PatchSiren cyber security CVE debrief

CVE-2026-77763 juicedata CVE debrief

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. This vulnerability highlights the importance of proper configuration management, monitoring, and incident response in preventing security breaches. By prioritizing patching and taking proactive measures, operators and administrators can protect their JuiceFS installations and prevent potential security breaches.

Vendor: juicedata
Product: juicefs
CVSS: HIGH 7.1
CISA KEV: Not listed in stored evidence
Original CVE published: 2026-08-21
Original CVE updated: 2026-08-21
Advisory published: 2026-08-21
Advisory updated: 2026-08-21

Who should care

Operators and administrators of JuiceFS installations, especially those using file:// stores or syncing from untrusted sources, should prioritize patching to prevent potential file writes outside configured directories. This includes reviewing configurations, monitoring for unusual activity, and considering compensating controls such as restricting write access to JuiceFS storage roots. Security teams and vulnerability management teams should also be aware of the potential impact and ensure proper mitigations are in place. Additionally, platform administrators and operators should verify the integrity of their JuiceFS deployments and ensure that they are not exposed to arbitrary file writes. Those responsible for asset inventory and configuration management should review their systems for potential exposure and prioritize patching accordingly. Furthermore, incident response teams should be prepared to respond to potential security incidents related to this vulnerability. IT and security teams should collaborate to ensure that all necessary measures are taken to mitigate the vulnerability and prevent potential security breaches. The vulnerability's high severity and potential impact on JuiceFS installations make it essential for operators and administrators to take immediate action to protect their systems. By prioritizing patching and taking proactive measures, operators can prevent potential security breaches and ensure the integrity of their JuiceFS deployments. Security teams should also consider implementing additional security controls, such as monitoring and detection systems, to identify and respond to potential security incidents related to this vulnerability. Effective communication and collaboration between IT and security teams are crucial to ensuring the successful mitigation of this vulnerability and preventing potential security breaches. The vulnerability highlights the importance of proper configuration management, monitoring, and incident response in preventing security breaches. By taking proactive measures and prioritizing patching, operators and administrators can protect their JuiceFS installations and prevent potential security breaches. In

Technical summary

The filestore backend in pkg/object/file.go did not properly check if file operations stayed beneath the root directory. This could allow an attacker to write to arbitrary locations on the system. The fix changes path() to return an error and rejects any key whose resolved path escapes the root. JuiceFS installations, especially those using file:// stores or syncing from untrusted sources, are affected.

Defensive priority

Operators of JuiceFS should prioritize patching to prevent potential file writes outside configured directories.

Recommended defensive actions

Review and apply the patch to ensure containment checks are performed
Inventory JuiceFS installations and configurations to identify potential exposure
Monitor for unusual file system activity
Consider compensating controls such as restricting write access to JuiceFS storage roots
Review configurations and ensure proper mitigations are in place
Verify the integrity of JuiceFS deployments and ensure that they are not exposed to arbitrary file writes
Ensure effective communication and collaboration between IT and security teams

Evidence notes

The CVE record indicates a high severity vulnerability in JuiceFS, with a CVSS score of 7.1. The vulnerability is related to the filestore backend in pkg/object/file.go, which did not properly check if file operations stayed beneath the root directory. This could allow an attacker to write to arbitrary locations on the system. The fix changes path() to return an error and rejects any key whose resolved path escapes the root. Operators 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, are therefore exposed to a file write at an attacker-influenced location. Evidence limits suggest verifying JuiceFS configurations and monitoring for unusual activity.

Official resources

AI-assisted PatchSiren debrief based on the supplied source corpus. The CVE record was published on 2026-08-21T11:17:06.937Z and has not been modified since then.