knowns versions before 0.31.0 fail to properly validate the x-opencode-directory request header in the /api/opencode

Published September 10, 2026 CVE-2026-88899

Knowns versions older than 0.31.0 let a remote user direct file operations outside the project folder. That can expose or change files on the host system.

Severity
CriticalCVSS 3.1 · 9.8
Fix
Fixed in 0.31.0Fix recorded yesterday
Affected versions
before 0.31.0
Weakness
CWE-73
Exploit likelihood
0.44% in 30 daysEPSS, higher than 37% of known flaws
Affects
knowns
Exploited
Not confirmedNo confirmation recorded
EU ID
EUVD-2026-75579ENISA vulnerability database

How it works

  • A remote client can provide a chosen directory in a request to Knowns' OpenCode proxy.
  • Older versions pass that directory to the OpenCode agent instead of enforcing the project folder.
  • The agent then performs file operations in the selected directory on the host system.

What to do

Run npm list knowns in each environment using the package. Versions below 0.31.0 are affected; version 0.31.0 or later is outside the published affected range.

Run this in the application environment you want to check:

npm list knowns

Upgrade Knowns to 0.31.0 or later. That release removed the embedded OpenCode proxy and Chat UI attack surface.

Technical details

CVE-2026-88899 is an unauthenticated directory-control flaw in Knowns' /api/opencode proxy. A network client can direct file operations outside the project root on the host system.

Severity breakdown

  • Attack vector Network Requires network access to the vulnerable service
  • Attack complexity Low Low complexity under the assessed conditions
  • Privileges required None Attacker needs no account or login
  • User interaction None No victim action needed
  • Scope Unchanged Impact stays within the same security authority
  • Confidentiality impact High Sensitive data can be exposed with serious impact
  • Integrity impact High Protected data can be changed with serious impact
  • Availability impact High The service can stop or suffer serious disruption
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Open in FIRST.org calculator

References

View Original Source