security: workbook path allowlist + stronger image polyglot validation (#54)

- dispo workbook imports are pinned to DISPO_IMPORT_DIR (default ./imports):
  tRPC input rejects absolute paths and .. segments, runtime reader
  re-validates containment via path.relative. Closes a path-traversal
  class that reached ExcelJS CVEs through admin/compromised tokens.
- image validator now checks the full 8-byte PNG magic, enforces PNG IEND
  and JPEG EOI trailers, scans the decoded buffer for markup polyglot
  markers (<script, <svg, <iframe, javascript:, onerror=, ...), and
  explicitly rejects SVG. Provider-generated covers (DALL-E, Gemini) run
  through the same validator before persistence — an untrusted upstream
  cannot smuggle a stored-XSS payload past us.
- added image-validation.test.ts and tightened documentation.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

packages/api/src/__tests__/assistant-tools-dispo-import-batch-delegation.test.ts

@@ -58,22 +58,22 @@ describe("assistant dispo import batch delegation tools", () => {
     const result = await executeTool(
       "stage_dispo_import_batch",
       JSON.stringify({
-        chargeabilityWorkbookPath: "/imports/chargeability.xlsx",
-        planningWorkbookPath: "/imports/planning.xlsx",
-        referenceWorkbookPath: "/imports/reference.xlsx",
-        costWorkbookPath: "/imports/cost.xlsx",
-        rosterWorkbookPath: "/imports/roster.xlsx",
+        chargeabilityWorkbookPath: "chargeability.xlsx",
+        planningWorkbookPath: "planning.xlsx",
+        referenceWorkbookPath: "reference.xlsx",
+        costWorkbookPath: "cost.xlsx",
+        rosterWorkbookPath: "roster.xlsx",
         notes: "March import",
       }),
       ctx,
     );
 
     expect(stageDispoImportBatch).toHaveBeenCalledWith(ctx.db, {
-      chargeabilityWorkbookPath: "/imports/chargeability.xlsx",
-      planningWorkbookPath: "/imports/planning.xlsx",
-      referenceWorkbookPath: "/imports/reference.xlsx",
-      costWorkbookPath: "/imports/cost.xlsx",
-      rosterWorkbookPath: "/imports/roster.xlsx",
+      chargeabilityWorkbookPath: "chargeability.xlsx",
+      planningWorkbookPath: "planning.xlsx",
+      referenceWorkbookPath: "reference.xlsx",
+      costWorkbookPath: "cost.xlsx",
+      rosterWorkbookPath: "roster.xlsx",
       notes: "March import",
     });
     expect(JSON.parse(result.content)).toEqual({
@@ -92,18 +92,18 @@ describe("assistant dispo import batch delegation tools", () => {
     const result = await executeTool(
       "validate_dispo_import_batch",
       JSON.stringify({
-        chargeabilityWorkbookPath: "/imports/chargeability.xlsx",
-        planningWorkbookPath: "/imports/planning.xlsx",
-        referenceWorkbookPath: "/imports/reference.xlsx",
+        chargeabilityWorkbookPath: "chargeability.xlsx",
+        planningWorkbookPath: "planning.xlsx",
+        referenceWorkbookPath: "reference.xlsx",
         importBatchId: "batch_1",
       }),
       ctx,
     );
 
     expect(assessDispoImportReadiness).toHaveBeenCalledWith({
-      chargeabilityWorkbookPath: "/imports/chargeability.xlsx",
-      planningWorkbookPath: "/imports/planning.xlsx",
-      referenceWorkbookPath: "/imports/reference.xlsx",
+      chargeabilityWorkbookPath: "chargeability.xlsx",
+      planningWorkbookPath: "planning.xlsx",
+      referenceWorkbookPath: "reference.xlsx",
       importBatchId: "batch_1",
     });
     expect(JSON.parse(result.content)).toEqual({

packages/api/src/__tests__/assistant-tools-project-cover-generate.test.ts

@@ -41,7 +41,7 @@ vi.mock("../ai-client.js", async (importOriginal) => {
     createDalleClient: vi.fn(() => ({
       images: {
         generate: vi.fn().mockResolvedValue({
-          data: [{ b64_json: "ZmFrZQ==" }],
+          data: [{ b64_json: "iVBORw0KGgoAAAAASUVORK5CYII=" }],
         }),
       },
     })),
@@ -49,10 +49,7 @@ vi.mock("../ai-client.js", async (importOriginal) => {
   };
 });
 
-import {
-  createToolContext,
-  executeTool,
-} from "./assistant-tools-project-media-test-helpers.js";
+import { createToolContext, executeTool } from "./assistant-tools-project-media-test-helpers.js";
 
 describe("assistant project cover generation tools", () => {
   beforeEach(() => {
@@ -60,7 +57,8 @@ describe("assistant project cover generation tools", () => {
   });
 
   it("routes project cover generation through the real project router path", async () => {
-    const projectFindUnique = vi.fn()
+    const projectFindUnique = vi
+      .fn()
       .mockResolvedValueOnce({
         id: "project_1",
         name: "Project One",
@@ -84,7 +82,7 @@ describe("assistant project cover generation tools", () => {
       });
     const projectUpdate = vi.fn().mockResolvedValue({
       id: "project_1",
-      coverImageUrl: "data:image/png;base64,ZmFrZQ==",
+      coverImageUrl: "data:image/png;base64,iVBORw0KGgoAAAAASUVORK5CYII=",
     });
     const ctx = createToolContext(
       {
@@ -119,7 +117,7 @@ describe("assistant project cover generation tools", () => {
 
     expect(projectUpdate).toHaveBeenCalledWith({
       where: { id: "project_1" },
-      data: { coverImageUrl: "data:image/png;base64,ZmFrZQ==" },
+      data: { coverImageUrl: "data:image/png;base64,iVBORw0KGgoAAAAASUVORK5CYII=" },
     });
     expect(projectFindUnique).toHaveBeenCalledWith({
       where: { id: "project_1" },

packages/api/src/__tests__/image-validation.test.ts

@@ -0,0 +1,82 @@
+import { describe, expect, it } from "vitest";
+import { validateImageDataUrl } from "../lib/image-validation.js";
+
+const PNG_HEADER = [0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a];
+const PNG_IEND = [0x49, 0x45, 0x4e, 0x44, 0xae, 0x42, 0x60, 0x82];
+const JPEG_HEADER = [0xff, 0xd8, 0xff, 0xe0];
+const JPEG_EOI = [0xff, 0xd9];
+
+function dataUrl(mime: string, bytes: number[]): string {
+  const base64 = Buffer.from(Uint8Array.from(bytes)).toString("base64");
+  return `data:${mime};base64,${base64}`;
+}
+
+describe("validateImageDataUrl", () => {
+  it("accepts a minimal well-formed PNG", () => {
+    const bytes = [...PNG_HEADER, 0x00, 0x00, 0x00, 0x00, ...PNG_IEND];
+    expect(validateImageDataUrl(dataUrl("image/png", bytes))).toEqual({ valid: true });
+  });
+
+  it("accepts a minimal well-formed JPEG", () => {
+    const bytes = [...JPEG_HEADER, 0x00, 0x00, ...JPEG_EOI];
+    expect(validateImageDataUrl(dataUrl("image/jpeg", bytes))).toEqual({ valid: true });
+  });
+
+  it("rejects SVG uploads explicitly", () => {
+    const svgBytes = Buffer.from("<svg xmlns='http://www.w3.org/2000/svg'/>", "utf8");
+    const base64 = svgBytes.toString("base64");
+    const result = validateImageDataUrl(`data:image/svg+xml;base64,${base64}`);
+    expect(result.valid).toBe(false);
+    if (!result.valid) expect(result.reason).toMatch(/SVG/i);
+  });
+
+  it("rejects a polyglot PNG with an HTML tail after IEND", () => {
+    const html = Buffer.from("<!doctype html><script>alert(1)</script>", "utf8");
+    const bytes = [...PNG_HEADER, 0x00, 0x00, 0x00, 0x00, ...PNG_IEND, ...Array.from(html)];
+    const result = validateImageDataUrl(dataUrl("image/png", bytes));
+    expect(result.valid).toBe(false);
+    // Either the IEND-trailer check or the polyglot scan is acceptable — both
+    // reject the payload before it reaches storage. A tail after IEND naturally
+    // fails the trailer check first.
+    if (!result.valid) expect(result.reason).toMatch(/IEND|polyglot/i);
+  });
+
+  it("rejects a PNG that does not end with IEND", () => {
+    // Declare PNG and include header but truncate before IEND
+    const bytes = [...PNG_HEADER, 0x00, 0x00, 0x00, 0x00];
+    const result = validateImageDataUrl(dataUrl("image/png", bytes));
+    expect(result.valid).toBe(false);
+    if (!result.valid) expect(result.reason).toMatch(/IEND/);
+  });
+
+  it("rejects a JPEG that does not end with the EOI marker", () => {
+    const bytes = [...JPEG_HEADER, 0x00, 0x00];
+    const result = validateImageDataUrl(dataUrl("image/jpeg", bytes));
+    expect(result.valid).toBe(false);
+    if (!result.valid) expect(result.reason).toMatch(/EOI/);
+  });
+
+  it("rejects a MIME/content mismatch", () => {
+    const bytes = [...PNG_HEADER, 0x00, ...PNG_IEND];
+    const result = validateImageDataUrl(dataUrl("image/jpeg", bytes));
+    expect(result.valid).toBe(false);
+    if (!result.valid) expect(result.reason).toMatch(/mismatch/i);
+  });
+
+  it("rejects a javascript: URL embedded in an EXIF-like comment", () => {
+    const marker = Buffer.from("javascript:alert(1)", "utf8");
+    const bytes = [...JPEG_HEADER, ...Array.from(marker), ...JPEG_EOI];
+    const result = validateImageDataUrl(dataUrl("image/jpeg", bytes));
+    expect(result.valid).toBe(false);
+    if (!result.valid) expect(result.reason).toMatch(/polyglot/i);
+  });
+
+  it("rejects a non-data-URL string", () => {
+    expect(validateImageDataUrl("not a data url").valid).toBe(false);
+  });
+
+  it("rejects an empty decoded buffer", () => {
+    const result = validateImageDataUrl("data:image/png;base64,");
+    expect(result.valid).toBe(false);
+  });
+});