Auth bypass in Bytedance Ui-Tars-Desktop
CVE-2026-81735
startServer.ts in the mcp-http-server package of UI-TARS-desktop defaulted its listen address to '::' when no host was given, so startSseAndStreamableHttpMcpServer bound the Streamable HTTP and SSE MCP transports to every interface, and its authentication middleware was optional: middlewares are applied only when a caller supplies them. The @agent-infra/mcp-server-commands and @agent-infra/mcp-server-filesystem entry points call startSseAndStreamableHttpMcpServer with a host and port alone and pass no middleware, so neither server required a credential. The commands server exposes a run_command tool that hands its caller-supplied command string to promisify(child_process.exec), so any unauthenticated client able to reach the port could run arbitrary commands as the user running the server, and the filesystem server exposed its file read and write tools on the same terms. The listen default became 127.0.0.1 in commit c2ad42e3eb9b27830db41a3e6f51ca7179d9b168; the package version stayed at 1.2.4 across that change, so the boundary is the commit rather than a release.
Vulnerability class: Broken Authentication
Published · last modified .
CVSS v3 metric
CVSS v3 base score 10.0 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H.
EPSS exploit prediction
EPSS: 0.008 (54.6th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 55th percentile — 54.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.005 · newest: 0.008 · change: +0.002
Affected products
Weakness classification (CWE)
References
- github.com/bytedance/UI-TARS-desktop/pull/1918 (issue-tracking, patch)
- github.com/bytedance/UI-TARS-desktop/commit/c2ad42e3eb9b27830db41a3e6f51ca7179d… (patch)
- github.com/bytedance/UI-TARS-desktop (product)
- github.com/bytedance/UI-TARS-desktop/blob/e9f3387288da4af2ad99972da2ac916cdabce… (technical-description)
- www.vulncheck.com/advisories/ui-tars-desktop-agent-infra-mcp-servers-bind-every… (third-party-advisory)
Frequently asked questions
- What is CVE-2026-81735?
- CVE-2026-81735 is a critical-severity vulnerability in Bytedance Ui-Tars-Desktop, classified under Missing Authentication for Critical Function. CVSS score: 10.0/10. Published 2026-08-27.
- How severe is CVE-2026-81735?
- Critical severity. CVSS v3 base score is 10.0 out of 10.