diff --git a/canvas/src/__tests__/csp-nonce.test.ts b/canvas/src/__tests__/csp-nonce.test.ts
index a76235aaa..317a3a466 100644
--- a/canvas/src/__tests__/csp-nonce.test.ts
+++ b/canvas/src/__tests__/csp-nonce.test.ts
@@ -41,6 +41,12 @@ describe("buildCsp — production", () => {
     expect(csp).toContain("object-src 'none'");
   });
 
+  it("allows blob: in frame-src for authenticated PDF previews", () => {
+    const frameSrc = csp.match(/frame-src[^;]*/)?.[0] ?? "";
+    expect(frameSrc).toContain("'self'");
+    expect(frameSrc).toContain("blob:");
+  });
+
   it("locks base-uri to 'self' (prevents base-tag injection)", () => {
     expect(csp).toContain("base-uri 'self'");
   });
diff --git a/canvas/src/middleware.ts b/canvas/src/middleware.ts
index 9442eb999..f904a6459 100644
--- a/canvas/src/middleware.ts
+++ b/canvas/src/middleware.ts
@@ -12,7 +12,9 @@ import type { NextRequest } from "next/server";
  *   • style-src retains 'unsafe-inline': React Flow positions nodes via
  *     element-level style="" attributes which cannot be nonce'd; CSS injection
  *     is significantly lower risk than script injection and is acceptable here.
- *   • object-src / base-uri / frame-ancestors locked to 'none'/'self'.
+ *   • object-src locked to 'none'; frame-src allows self + blob: for
+ *     browser-native PDF previews backed by authenticated Blob URLs.
+ *   • base-uri / frame-ancestors locked to 'self'/'none'.
  *   • upgrade-insecure-requests forces HTTPS on mixed-content.
  *
  * Development — permissive policy:
@@ -61,6 +63,7 @@ export function buildCsp(nonce: string, isDev: boolean): string {
     "img-src 'self' blob: data:",
     "font-src 'self'",
     "object-src 'none'",
+    "frame-src 'self' blob:",
     "base-uri 'self'",
     "form-action 'self'",
     "frame-ancestors 'none'",
diff --git a/workspace-server/internal/middleware/securityheaders.go b/workspace-server/internal/middleware/securityheaders.go
index 2f96ff14d..c9aa1470e 100644
--- a/workspace-server/internal/middleware/securityheaders.go
+++ b/workspace-server/internal/middleware/securityheaders.go
@@ -23,7 +23,7 @@ var apiPrefixes = []string{
 	"/settings",
 	"/bundles",
 	"/org",
-	"/orgs",   // #610 — per-org plugin allowlist routes
+	"/orgs", // #610 — per-org plugin allowlist routes
 	"/templates",
 	"/plugins",
 	"/webhooks",
@@ -95,6 +95,7 @@ func SecurityHeaders() gin.HandlerFunc {
 					"script-src 'self' 'unsafe-inline'; "+
 					"style-src 'self' 'unsafe-inline'; "+
 					"img-src 'self' data: blob:; "+
+					"frame-src 'self' blob:; "+
 					"connect-src 'self' ws: wss:; "+
 					"font-src 'self' data:")
 		}
diff --git a/workspace-server/internal/middleware/securityheaders_test.go b/workspace-server/internal/middleware/securityheaders_test.go
index 885eef4fb..2f3e6d4b8 100644
--- a/workspace-server/internal/middleware/securityheaders_test.go
+++ b/workspace-server/internal/middleware/securityheaders_test.go
@@ -57,6 +57,7 @@ func TestSecurityHeaders(t *testing.T) {
 		"script-src 'self' 'unsafe-inline'",
 		"style-src 'self' 'unsafe-inline'",
 		"img-src 'self' data: blob:",
+		"frame-src 'self' blob:",
 		"connect-src 'self' ws: wss:",
 		"font-src 'self' data:",
 	} {
@@ -195,6 +196,9 @@ func TestCSPCanvasRoutesGetPermissivePolicy(t *testing.T) {
 			if strings.Contains(csp, "'unsafe-eval'") {
 				t.Errorf("canvas path %q: CSP must not contain 'unsafe-eval', got %q", path, csp)
 			}
+			if !strings.Contains(csp, "frame-src 'self' blob:") {
+				t.Errorf("canvas path %q: CSP should allow blob: frames for PDF previews, got %q", path, csp)
+			}
 		})
 	}
 }
@@ -267,7 +271,7 @@ func TestIsAPIPath(t *testing.T) {
 		{"/ws", true},
 		{"/events", true},
 		{"/approvals", true},
-		{"/orgs", true},                          // #610 allowlist routes
+		{"/orgs", true}, // #610 allowlist routes
 		{"/orgs/org-1/plugins/allowlist", true},
 		// Sub-paths
 		{"/workspaces/abc-123", true},