CVE-2026-86540: Knowns: untrusted LSP binary path allows code execution

## Overview A critical **Arbitrary Code Execution (ACE)** vulnerability exists in the Knowns Language Server Protocol (LSP) detection and startup pipeline. The system blindly trusts the `settings.lsp.languages.<lang>.binary` field defined in the project-level `.knowns/config.json` file. Because this field is **never validated** against an allowlist of managed binaries, and absolute paths are implicitly accepted, opening a malicious repository (or a legitimate repository where the config has been tampered with) results in the immediate execution of an attacker-controlled binary. The payload is executed **twice** per session: once during the initial `runVersionCheck` (health check), and again when the LSP server process is spawned via `Server.Start()`. When chained with the previously identified Config Overwrite vulnerabilities, this flaw yields a fully unauthenticated Remote Code Execution chain. ## Affected paths | File Path | Role | Vulnerability & Execution Impact | | :--- | :--- | :--- | | **`internal/models/config.go`** | Validation Gap | **Missing Binary Validation (CWE-829):** `ProjectSettings.Validate()` enforces duration formats for task lifecycles but **completely ignores** the `LSPLanguageSettings.Binary` field. Absolute paths, shell interpreters, and untrusted executables are silently accepted. | | **`internal/lsp/detect.go`** | Execution Sink #1 | **Unsanitized Health Check Execution:** `Detector.resolve()` passes the unvalidated override to `exec.LookPath()`, then invokes `runVersionCheck()` which blindly calls `cmd.Run()` on the attacker-controlled binary with `CheckArgs`. | | **`internal/lsp/server.go`** | Execution Sink #2 | **Unsanitized LSP Server Spawn:** `Server.Start()` passes the resolved binary path to `knownsprocess.Command()` and spawns it as a long-running background process via `cmd.Start()`, executing the payload a second time. | ## Root Cause ### Missing Validation in Configuration Schema In `internal/models/config.go`, the `ProjectSettings.Validate()` function is responsible for sanitizing the project configuration loaded from `.knowns/config.json`. However, it only validates task lifecycle durations: ```go func (s ProjectSettings) Validate() error { settings := s.EffectiveTaskLifecycle() if _, err := ParseTaskLifecycleDuration(settings.ArchiveAfter); err != nil { ... } // NO VALIDATION FOR s.LSP.Languages[lang].Binary return nil } ``` The `LSPLanguageSettings` struct exposes a `Binary` string field. When a malicious project is loaded, this string is passed unmodified into the LSP resolution pipeline. ### Blind Execution in LSP Detector In `internal/lsp/detect.go`, the `Detector.resolve()` function accepts an `override` string (from the config) and forces it into the execution pipeline: ```go func (d *Detector) resolve(ctx context.Context, root string, lang Language, override string) (ServerCommand, bool) { binaries := lang.Binaries if override != "" { binary := Binary{Name: override} // Attacker's malicious path injected here binaries = []Binary{binary} } for _, binary := range binaries { path, err := d.LookPath(binary.Name) // Accepts absolute paths (e.g., /tmp/evil.sh) // ... err = d.RunCheck(checkCtx, path, binary.CheckArgs...) // EXECUTION #1 // ... } } ``` `d.RunCheck` maps to `runVersionCheck`, which executes the binary via `knownsprocess.CommandContext(ctx, path, args...).Run()`. ### Unrestricted Process Spawn In `internal/lsp/server.go`, when the LSP manager starts the server, it executes the same compromised path: ```go func (s *Server) Start(ctx context.Context) error { // ... cmd := knownsprocess.Command(s.Command.Path, s.Command.Args...) // EXECUTION #2 cmd.Dir = s.Root // ... if err := cmd.Start(); err != nil { ... } } ``` ## Attack Vector | Phase | Request / Action | Effect | | :--- | :--- | :--- | | **1. Plant** | Attacker commits `.knowns/config.json` containing `{"settings":{"lsp":{"languages":{"go":{"binary":"/tmp/evil.sh"}}}}}` to a repository. | Malicious config embedded in the project. | | **2. Trigger** | Victim (or AI Agent) clones the repo and opens it with `knowns mcp` or `knowns browser`. | Auto-detection scans the project, finds a `.go` file, and loads the malicious config. | | **3. Execute (Health Check)** | `Detector.resolve()` calls `runVersionCheck("/tmp/evil.sh", "version")`. | **RCE Execution #1** occurs silently in the background. | | **4. Execute (LSP Spawn)** | `Server.Start()` calls `cmd.Start()` with the same binary. | **RCE Execution #2** occurs, spawning the malicious process as a long-running daemon. | **Chained Attack Vector (Unauthenticated RCE):** If combined with the **Config Overwrite** vulnerability (via `code.replace` path traversal), a remote attacker can overwrite `.knowns/config.json` in a target project, inject a payload, and trigger an LSP restart (via `docs.update` or server reload), achieving **Remote Code Execution without any user interaction**. ## Analysis This vulnerability is a textbook example of **Inclusion of Functionality from Untrusted Control Sphere (CWE-829)**, commonly known in the IDE/Editor space as the "Malicious Workspace" vulnerability (similar to historical CVEs in VS Code where `.vscode/settings.json` could point to malicious interpreter paths). The core failure is the lack of a strict allowlist for executable paths. By relying on `exec.LookPath()`, the code allows an attacker to bypass binary name resolution simply by providing an absolute path (`/abs/path/evil.sh`) or a path containing a slash (`./evil.sh`). Furthermore, the execution happens **automatically** upon project load. In modern AI-driven development workflows, AI Agents automatically scan project files (like `.go`, `.ts`, `.py`) to provide context. The LSP detector triggers on file extensions, meaning the victim or agent does not even need to explicitly run a "build" or "start" command; the mere act of the Agent indexing the workspace triggers the payload. ## Fix *Patch is available right now at [New Release](https://github.com/knowns-dev/knowns/releases).*

An attacker publishes or submits a pull request to a popular repository that adds `.knowns/config.json` setting the Go language server binary to a bundled script such as ./evil.sh (or an absolute path to a dropped file). A developer or an autonomous coding agent clones the repo and starts Knowns through MCP. LSP detection sees a .go file, loads the config and runs the script as a version check, then spawns it again as the language server. The script steals SSH keys, cloud credentials and LLM API keys, and keeps running as a background process. In the chained variant, an attacker with a path traversal write primitive overwrites the config in a target project and forces an LSP restart to get code execution remotely.