A critical authentication bypass in Cua's computer-server (CVSS 9.8) lets unauthenticated network attackers run arbitrary shell commands on hosts running versions before 0.3.42.
What Is It
Cua computer-server versions before 0.3.42 skip authentication entirely when the CONTAINER_NAME environment variable is unset, and the service binds to all interfaces by default. The combination, missing authentication for a critical function (CWE-306) plus a permissive default bind, exposes the full control surface of the server to anyone who can reach it on the network.
Attackers who reach TCP port 8000 can execute shell commands through the run_command endpoint, read and write arbitrary files via the file operation endpoints, and open interactive PTY shells. None of this requires credentials, user interaction, or elevated privileges.
Why It Matters
The CVSS 3.1 base score is 9.8 (CRITICAL), vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. A secondary CVSS 4.0 score of 9.3 (CRITICAL) was also assigned. Attack vector is network, attack complexity is low, and confidentiality, integrity, and availability impacts are all rated high.
In practical terms: a single unauthenticated request to an exposed instance yields command execution as the server process. Arbitrary file read/write and PTY access mean a foothold converts directly into persistence and data theft. Because the vulnerable default is "no auth, listen everywhere," misconfiguration is not required; deploying the software without setting CONTAINER_NAME is enough.
The CVE is not listed in the CISA KEV catalog, so there is no confirmation of active exploitation at this time, and no KEV due date or required action applies.
What's Vulnerable
- Vendor: trycua
- Product: cua-computer-server (
pkg:pypi/cua-computer-server) - Affected versions: all versions before 0.3.42 (default status for other versions: unaffected)
- Exposed service: TCP port 8000, bound to all interfaces by default
Patch Status
Upgrade to cua-computer-server 0.3.42 or later. The fix is tracked in commit 59cf25c0ec54 and issue #1892 in the trycua/cua repository. NVD status is "Received" as of 2026-09-05, with the record sourced from VulnCheck.
Sources
- NVD, CVE-2026-86121: https://nvd.nist.gov/vuln/detail/CVE-2026-86121
- VulnCheck Advisory; cua-computer-server before 0.3.42 unauthenticated RCE via desktop control: https://www.vulncheck.com/advisories/cua-computer-server-before-0.3.42-unauthenticated-rce-via-desktop-control
- trycua/cua repository: https://github.com/trycua/cua
- Fix commit
59cf25c0ec54: https://github.com/trycua/cua/commit/59cf25c0ec54 - Issue #1892: https://github.com/trycua/cua/issues/1892