fix(cli): confine downloaded skills to the cache directory

packages/opencode/src/skill/discovery.ts

@@ -71,8 +71,22 @@ export const layer: Layer.Layer<Service, never, FSUtil.Service | Path.Path | Htt
       )
       const list = data.skills.filter((skill) => skill.files.includes("SKILL.md"))
 
+      // kilocode_change start - remote index.json controls skill.name/file, so a crafted `../` could escape the
+      // cache and plant a SKILL.md in a trusted dir (e.g. ~/.agents/skills). Drop any skill whose paths escape it.
+      const rooted = (target: string) => {
+        const rel = path.relative(cache, target)
+        return rel !== "" && !rel.startsWith("..") && !path.isAbsolute(rel)
+      }
+      const safe: typeof list = []
+      for (const skill of list) {
+        const root = path.join(cache, skill.name)
+        if (rooted(root) && skill.files.every((file) => rooted(path.join(root, file)))) safe.push(skill)
+        else yield* Effect.logWarning("skipping skill with unsafe path", { url: index, skill: skill.name })
+      }
+      // kilocode_change end
+
       const dirs = yield* Effect.forEach(
-        list,
+        safe, // kilocode_change - was `list`; drop skills whose paths escape the cache
         (skill) =>
           Effect.gen(function* () {
             const root = path.join(cache, skill.name)

packages/opencode/test/skill/discovery.test.ts

@@ -24,6 +24,15 @@ beforeAll(async () => {
     async fetch(req) {
       const url = new URL(req.url)
 
+      // kilocode_change start - serve a crafted index whose skill name escapes the cache via `../`
+      if (url.pathname === "/evil/index.json") {
+        return Response.json({ skills: [{ name: "../../../.agents/skills/evil", files: ["SKILL.md"] }] })
+      }
+      if (url.pathname.endsWith("/.agents/skills/evil/SKILL.md")) {
+        return new Response("---\nname: evil\ndescription: evil.\n---\npwned")
+      }
+      // kilocode_change end
+
       // route /.well-known/skills/* to the fixture directory
       if (url.pathname.startsWith("/.well-known/skills/")) {
         const filePath = url.pathname.replace("/.well-known/skills/", "")
@@ -114,6 +123,20 @@ describe("Discovery.pull", () => {
     }),
   )
 
+  // kilocode_change start - path-traversal in the remote index must not plant a trusted skill
+  it.live("rejects a skill name that escapes the cache directory", () =>
+    Effect.gen(function* () {
+      const fsys = yield* FSUtil.Service
+      const discovery = yield* Discovery.Service
+      const dirs = yield* discovery.pull(`http://localhost:${server.port}/evil/`)
+      // the traversal skill is skipped, nothing is planted outside the cache
+      expect(dirs).toEqual([])
+      const escaped = path.join(cacheDir, "../../../.agents/skills/evil/SKILL.md")
+      expect(yield* fsys.existsSafe(escaped)).toBe(false)
+    }),
+  )
+  // kilocode_change end
+
   it.live("caches downloaded files on second pull", () =>
     Effect.gen(function* () {
       // clear dir and downloadCount