From f64694f894e5f7690f09e7ad5efb2aa4c1c7c1f2 Mon Sep 17 00:00:00 2001
From: Chris Farhood <chris@farhood.org>
Date: Thu, 23 Apr 2026 23:53:18 +0000
Subject: [PATCH] fix: validate companyId/instanceId against path traversal
 (N1)

Co-Authored-By: Claude Sonnet <noreply@anthropic.com>
Co-Authored-By: Paperclip <noreply@paperclip.ing>
---
 src/server/prompt-cache.test.ts | 49 +++++++++++++++++++++++++++++++++
 src/server/prompt-cache.ts      |  9 ++++++
 2 files changed, 58 insertions(+)
 create mode 100644 src/server/prompt-cache.test.ts

diff --git a/src/server/prompt-cache.test.ts b/src/server/prompt-cache.test.ts
new file mode 100644
index 0000000..dc14372
--- /dev/null
+++ b/src/server/prompt-cache.test.ts
@@ -0,0 +1,49 @@
+import { describe, it, expect, vi } from "vitest";
+import os from "node:os";
+import path from "node:path";
+import { prepareClaudePromptBundle } from "./prompt-cache.js";
+
+const onLog = vi.fn();
+
+describe("prepareClaudePromptBundle path traversal validation", () => {
+  const validArgs = {
+    skills: [],
+    instructionsContents: null,
+    onLog,
+  };
+
+  it("rejects companyId containing ..", async () => {
+    await expect(prepareClaudePromptBundle({ ...validArgs, companyId: ".." })).rejects.toThrow(/companyId/);
+  });
+
+  it("rejects companyId containing ../x", async () => {
+    await expect(prepareClaudePromptBundle({ ...validArgs, companyId: "../x" })).rejects.toThrow(/companyId/);
+  });
+
+  it("rejects companyId containing /", async () => {
+    await expect(prepareClaudePromptBundle({ ...validArgs, companyId: "a/b" })).rejects.toThrow(/companyId/);
+  });
+
+  it("rejects companyId containing backslash", async () => {
+    await expect(prepareClaudePromptBundle({ ...validArgs, companyId: "a\\b" })).rejects.toThrow(/companyId/);
+  });
+
+  it("rejects companyId containing null byte", async () => {
+    await expect(prepareClaudePromptBundle({ ...validArgs, companyId: "a\0b" })).rejects.toThrow(/companyId/);
+  });
+
+  it("rejects empty companyId", async () => {
+    await expect(prepareClaudePromptBundle({ ...validArgs, companyId: "" })).rejects.toThrow(/companyId/);
+  });
+
+  it("rejects whitespace-only companyId", async () => {
+    await expect(prepareClaudePromptBundle({ ...validArgs, companyId: "   " })).rejects.toThrow(/companyId/);
+  });
+
+  it("accepts a valid companyId", async () => {
+    vi.stubEnv("PAPERCLIP_HOME", path.join(os.tmpdir(), `prompt-cache-test-${process.pid}`));
+    const result = await prepareClaudePromptBundle({ ...validArgs, companyId: "acme-co" });
+    expect(result.rootDir).toContain("acme-co");
+    vi.unstubAllEnvs();
+  });
+});
diff --git a/src/server/prompt-cache.ts b/src/server/prompt-cache.ts
index 6ab06fb..6fcc2ea 100644
--- a/src/server/prompt-cache.ts
+++ b/src/server/prompt-cache.ts
@@ -21,6 +21,13 @@ export interface ClaudePromptBundle {
 
 const DEFAULT_PAPERCLIP_INSTANCE_ID = "default";
 
+function validatePathComponent(value: string, fieldName: string): void {
+  if (value.trim().length === 0) throw new Error(`Invalid ${fieldName}: must not be empty`);
+  if (value.includes("/") || value.includes("\\")) throw new Error(`Invalid ${fieldName}: must not contain path separators`);
+  if (value.includes("..")) throw new Error(`Invalid ${fieldName}: must not contain ".."`);
+  if (value.includes("\0")) throw new Error(`Invalid ${fieldName}: must not contain null bytes`);
+}
+
 function resolveManagedClaudePromptCacheRoot(companyId: string): string {
   const paperclipHome =
     (typeof process.env.PAPERCLIP_HOME === "string" && process.env.PAPERCLIP_HOME.trim().length > 0
@@ -31,6 +38,8 @@ function resolveManagedClaudePromptCacheRoot(companyId: string): string {
     (typeof process.env.PAPERCLIP_INSTANCE_ID === "string" && process.env.PAPERCLIP_INSTANCE_ID.trim().length > 0
       ? process.env.PAPERCLIP_INSTANCE_ID.trim()
       : null) ?? DEFAULT_PAPERCLIP_INSTANCE_ID;
+  validatePathComponent(companyId, "companyId");
+  validatePathComponent(instanceId, "instanceId");
   return path.resolve(paperclipHome, "instances", instanceId, "companies", companyId, "claude-prompt-cache");
 }