diff --git a/apps/sim/lib/api/contracts/custom-blocks.ts b/apps/sim/lib/api/contracts/custom-blocks.ts
index 01adbbddfc0..e7629109324 100644
--- a/apps/sim/lib/api/contracts/custom-blocks.ts
+++ b/apps/sim/lib/api/contracts/custom-blocks.ts
@@ -63,13 +63,27 @@ export const listCustomBlocksQuerySchema = z.object({
   workspaceId: workspaceIdSchema,
 })
 
+/**
+ * Icon URLs are rendered as org-wide `<img>` sources, so only https URLs and
+ * internal file-serve paths (what the icon upload UI stores) are accepted —
+ * never data:/blob:/other schemes an admin could smuggle into shared metadata.
+ * Shared with the copilot deploy_custom_block handler's pass-through branch.
+ */
+export function isAllowedCustomBlockIconUrl(value: string): boolean {
+  return value.startsWith('https://') || value.startsWith('/api/files/serve/')
+}
+
+const iconUrlSchema = z.string().min(1).max(2048).refine(isAllowedCustomBlockIconUrl, {
+  message: 'iconUrl must be an https URL or an internal /api/files/serve/ path',
+})
+
 export const publishCustomBlockBodySchema = z.object({
   workspaceId: workspaceIdSchema,
   workflowId: workflowIdSchema,
   name: z.string().min(1, 'Name is required').max(60, 'Name must be 60 characters or fewer'),
   description: z.string().max(280, 'Description must be 280 characters or fewer').default(''),
-  /** Uploaded icon image URL; omit for the default icon. */
-  iconUrl: z.string().min(1).max(2048).optional(),
+  /** Uploaded icon image URL (https or internal serve path); omit for the default icon. */
+  iconUrl: iconUrlSchema.optional(),
   /** Per-input placeholder hints keyed by Start field id; the field set itself is always derived from the deployment. */
   inputs: z.array(inputPlaceholderSchema).max(50).optional(),
   /** Curated outputs; omit/empty to expose the child's whole result. */
@@ -87,8 +101,8 @@ export const updateCustomBlockBodySchema = z
     name: z.string().min(1).max(60).optional(),
     description: z.string().max(280).optional(),
     enabled: z.boolean().optional(),
-    /** A URL sets/replaces the icon; `null` clears it (default icon). */
-    iconUrl: z.string().min(1).max(2048).nullable().optional(),
+    /** A URL (https or internal serve path) sets/replaces the icon; `null` clears it (default icon). */
+    iconUrl: iconUrlSchema.nullable().optional(),
     inputs: z.array(inputPlaceholderSchema).max(50).optional(),
     exposedOutputs: z.array(exposedOutputSchema).max(50).optional(),
   })
diff --git a/apps/sim/lib/copilot/tools/handlers/deployment/custom-block.test.ts b/apps/sim/lib/copilot/tools/handlers/deployment/custom-block.test.ts
index b5e8850c279..480d33a801e 100644
--- a/apps/sim/lib/copilot/tools/handlers/deployment/custom-block.test.ts
+++ b/apps/sim/lib/copilot/tools/handlers/deployment/custom-block.test.ts
@@ -388,6 +388,29 @@ describe('executeDeployCustomBlock', () => {
     expect(publishCustomBlockMock).not.toHaveBeenCalled()
   })
 
+  it('rejects non-https icon URL schemes on pass-through', async () => {
+    const dataUri = await executeDeployCustomBlock(
+      { name: 'Enrich Lead', iconUrl: 'data:image/svg+xml;base64,PHN2Zy8+' },
+      context
+    )
+    expect(dataUri.success).toBe(false)
+    expect(dataUri.error).toContain('https')
+
+    const plainHttp = await executeDeployCustomBlock(
+      { name: 'Enrich Lead', iconUrl: 'http://example.com/icon.png' },
+      context
+    )
+    expect(plainHttp.success).toBe(false)
+    expect(publishCustomBlockMock).not.toHaveBeenCalled()
+
+    publishCustomBlockMock.mockResolvedValue(publishedBlock)
+    const servePath = await executeDeployCustomBlock(
+      { name: 'Enrich Lead', iconUrl: '/api/files/serve/workspace-logos%2Ficon.png' },
+      context
+    )
+    expect(servePath.success).toBe(true)
+  })
+
   it('fails when the icon workspace file is not an image', async () => {
     listWorkspaceFilesMock.mockResolvedValue([
       { name: 'notes.pdf', folderPath: null, type: 'application/pdf', size: 1024, key: 'k' },
diff --git a/apps/sim/lib/copilot/tools/handlers/deployment/custom-block.ts b/apps/sim/lib/copilot/tools/handlers/deployment/custom-block.ts
index 65d2bed86d6..36268f6216f 100644
--- a/apps/sim/lib/copilot/tools/handlers/deployment/custom-block.ts
+++ b/apps/sim/lib/copilot/tools/handlers/deployment/custom-block.ts
@@ -1,6 +1,7 @@
 import { AuditAction, AuditResourceType, recordAudit } from '@sim/audit'
 import { toError } from '@sim/utils/errors'
 import { generateShortId } from '@sim/utils/id'
+import { isAllowedCustomBlockIconUrl } from '@/lib/api/contracts/custom-blocks'
 import { isOrganizationOnEnterprisePlan } from '@/lib/billing'
 import type { ExecutionContext, ToolCallResult } from '@/lib/copilot/request/types'
 import { canonicalizeVfsPath, canonicalWorkspaceFilePath } from '@/lib/copilot/vfs/path-utils'
@@ -42,7 +43,14 @@ async function resolveIconUrl(
 ): Promise<string | undefined> {
   const value = raw?.trim()
   if (!value) return undefined
-  if (!value.startsWith('files/')) return value
+  if (!value.startsWith('files/')) {
+    if (!isAllowedCustomBlockIconUrl(value)) {
+      throw new CustomBlockValidationError(
+        'iconUrl must be an https URL, an internal /api/files/serve/ path, or a workspace file path (files/...)'
+      )
+    }
+    return value
+  }
 
   const canonical = canonicalizeVfsPath(value)
   const files = await listWorkspaceFiles(workspaceId, { hydrateFolderPaths: true })