diff --git a/apps/api/plane/settings/common.py b/apps/api/plane/settings/common.py
index 68ea06dbdc..25a212e763 100644
--- a/apps/api/plane/settings/common.py
+++ b/apps/api/plane/settings/common.py
@@ -473,7 +473,6 @@ ATTACHMENT_MIME_TYPES = [
     "application/vnd.openxmlformats-officedocument.presentationml.presentation",
     "text/plain",
     "text/markdown",
-    "text/mdx",
     "application/rtf",
     "application/vnd.oasis.opendocument.spreadsheet",
     "application/vnd.oasis.opendocument.text",
@@ -541,6 +540,8 @@ ATTACHMENT_MIME_TYPES = [
     "application/x-sql",
     # Gzip
     "application/x-gzip",
+    # Markdown
+    "text/markdown",
 ]
 
 # MIME types that browsers can execute as scripts when served inline.
diff --git a/apps/web/core/components/icons/attachment/attachment-icon.test.tsx b/apps/web/core/components/icons/attachment/attachment-icon.test.tsx
new file mode 100644
index 0000000000..ab83b0b186
--- /dev/null
+++ b/apps/web/core/components/icons/attachment/attachment-icon.test.tsx
@@ -0,0 +1,24 @@
+/**
+ * Copyright (c) 2023-present Plane Software, Inc. and contributors
+ * SPDX-License-Identifier: AGPL-3.0-only
+ * See the LICENSE file for details.
+ */
+
+import { describe, expect, it } from "vitest";
+
+import { DefaultIcon, TxtIcon } from "@/components/icons/attachment";
+
+import { getFileIcon } from "./attachment-icon";
+
+describe("getFileIcon", () => {
+  it.each(["md", "markdown", "mdx", "MD", "MARKDOWN", "MDX"])(
+    "uses the text icon for the %s extension",
+    (extension) => {
+      expect(getFileIcon(extension).type).toBe(TxtIcon);
+    }
+  );
+
+  it("uses the default icon for an unknown extension", () => {
+    expect(getFileIcon("unknown").type).toBe(DefaultIcon);
+  });
+});
diff --git a/apps/web/core/components/issues/attachment/attachment-detail.tsx b/apps/web/core/components/issues/attachment/attachment-detail.tsx
index fb486b04b1..aa48959197 100644
--- a/apps/web/core/components/issues/attachment/attachment-detail.tsx
+++ b/apps/web/core/components/issues/attachment/attachment-detail.tsx
@@ -53,7 +53,7 @@ export const IssueAttachmentsDetail = observer(function IssueAttachmentsDetail(p
   // derived values
   const attachment = attachmentId ? getAttachmentById(attachmentId) : undefined;
   const fileName = getFileName(attachment?.attributes.name ?? "");
-  const fileExtension = getFileExtension(attachment?.asset_url ?? "");
+  const fileExtension = getFileExtension(attachment?.attributes.name ?? "");
   const fileIcon = getFileIcon(fileExtension, 28);
   const fileURL = getFileURL(attachment?.asset_url ?? "");
   // hooks
diff --git a/apps/web/package.json b/apps/web/package.json
index 9fbf4caf9a..9e7a89f9d5 100644
--- a/apps/web/package.json
+++ b/apps/web/package.json
@@ -7,6 +7,7 @@
   "scripts": {
     "dev": "react-router dev --port 3000",
     "build": "react-router build",
+    "test": "vitest run",
     "preview": "react-router build && serve -s build/client -l 3000",
     "start": "serve -s build/client -l 3000",
     "clean": "rm -rf .turbo && rm -rf .next && rm -rf .react-router && rm -rf node_modules && rm -rf dist && rm -rf build",
@@ -86,6 +87,7 @@
     "dotenv": "catalog:",
     "typescript": "catalog:",
     "vite": "catalog:",
-    "vite-tsconfig-paths": "catalog:"
+    "vite-tsconfig-paths": "catalog:",
+    "vitest": "catalog:"
   }
 }
diff --git a/apps/web/vitest.config.ts b/apps/web/vitest.config.ts
new file mode 100644
index 0000000000..e3137f0672
--- /dev/null
+++ b/apps/web/vitest.config.ts
@@ -0,0 +1,17 @@
+/**
+ * Copyright (c) 2023-present Plane Software, Inc. and contributors
+ * SPDX-License-Identifier: AGPL-3.0-only
+ * See the LICENSE file for details.
+ */
+
+import { defineConfig } from "vitest/config";
+
+export default defineConfig({
+  resolve: {
+    tsconfigPaths: true,
+  },
+  test: {
+    environment: "node",
+    include: ["core/**/*.test.{ts,tsx}"],
+  },
+});
diff --git a/packages/editor/src/core/constants/config.ts b/packages/editor/src/core/constants/config.ts
index 9e126fa2a7..64508e63e0 100644
--- a/packages/editor/src/core/constants/config.ts
+++ b/packages/editor/src/core/constants/config.ts
@@ -33,7 +33,6 @@ export const ACCEPTED_ATTACHMENT_MIME_TYPES = [
   "application/vnd.openxmlformats-officedocument.presentationml.presentation",
   "text/plain",
   "text/markdown",
-  "text/mdx",
   "application/rtf",
   "audio/mpeg",
   "audio/wav",
diff --git a/packages/services/package.json b/packages/services/package.json
index 7f988cc048..b02e65fb41 100644
--- a/packages/services/package.json
+++ b/packages/services/package.json
@@ -14,6 +14,7 @@
   "scripts": {
     "build": "tsdown",
     "dev": "tsdown --watch --no-clean",
+    "test": "vitest run",
     "check:lint": "oxlint --max-warnings=6 .",
     "check:types": "tsc --noEmit",
     "check:format": "oxfmt --check .",
@@ -30,6 +31,7 @@
   "devDependencies": {
     "@plane/typescript-config": "workspace:*",
     "tsdown": "catalog:",
-    "typescript": "catalog:"
+    "typescript": "catalog:",
+    "vitest": "catalog:"
   }
 }
diff --git a/packages/services/src/file/helper.test.ts b/packages/services/src/file/helper.test.ts
new file mode 100644
index 0000000000..85265f057f
--- /dev/null
+++ b/packages/services/src/file/helper.test.ts
@@ -0,0 +1,60 @@
+/**
+ * Copyright (c) 2023-present Plane Software, Inc. and contributors
+ * SPDX-License-Identifier: AGPL-3.0-only
+ * See the LICENSE file for details.
+ */
+
+import { afterEach, describe, expect, it, vi } from "vitest";
+
+import { getFileMetaDataForUpload } from "./helper";
+
+const createFile = (name: string, contents: BlobPart[] = ["# Markdown"]): File =>
+  new File(contents, name, { type: "" });
+
+describe("getFileMetaDataForUpload", () => {
+  afterEach(() => {
+    vi.restoreAllMocks();
+  });
+
+  it.each(["notes.md", "notes.markdown", "notes.mdx", "NOTES.MD", "NOTES.MDX"])(
+    "detects %s as Markdown from its extension",
+    async (filename) => {
+      const metadata = await getFileMetaDataForUpload(createFile(filename));
+
+      expect(metadata.type).toBe("text/markdown");
+    }
+  );
+
+  it.each([
+    "",
+    ".notes.md",
+    "folder/notes.md",
+    "folder\\notes.mdx",
+    "notes.exe",
+    "notes.exe.md",
+    "notes.EXE.mdx",
+    "notes.exe.safe.md",
+  ])("rejects unsafe filename %s", async (filename) => {
+    vi.spyOn(console, "warn").mockImplementation(() => undefined);
+
+    const metadata = await getFileMetaDataForUpload(createFile(filename));
+
+    expect(metadata.type).toBe("");
+  });
+
+  it("returns an empty type for an unsupported extension without a detectable signature", async () => {
+    const metadata = await getFileMetaDataForUpload(createFile("notes.bin"));
+
+    expect(metadata.type).toBe("");
+  });
+
+  it("prefers a detected signature over the filename extension", async () => {
+    const pngHeader = new Uint8Array([
+      0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a, 0x00, 0x00, 0x00, 0x0d, 0x49, 0x48, 0x44, 0x52, 0x00, 0x00, 0x00,
+      0x01, 0x00, 0x00, 0x00, 0x01, 0x08, 0x06, 0x00, 0x00, 0x00, 0x1f, 0x15, 0xc4, 0x89,
+    ]);
+    const metadata = await getFileMetaDataForUpload(createFile("image.md", [pngHeader]));
+
+    expect(metadata.type).toBe("image/png");
+  });
+});
diff --git a/packages/services/src/file/helper.ts b/packages/services/src/file/helper.ts
index 19635f06f4..8d3b590480 100644
--- a/packages/services/src/file/helper.ts
+++ b/packages/services/src/file/helper.ts
@@ -17,7 +17,7 @@ import { DANGEROUS_EXTENSIONS } from "@plane/constants";
 const EXTENSION_MIME_TYPE_MAP: Record<string, string> = {
   md: "text/markdown",
   markdown: "text/markdown",
-  mdx: "text/mdx",
+  mdx: "text/markdown",
 };
 
 /**
@@ -54,12 +54,11 @@ const validateFilename = (filename: string): string | null => {
 
   const parts = filename.split(".");
 
-  // Check for double extensions with dangerous patterns
-  if (parts.length >= 3) {
-    const secondLastExt = parts[parts.length - 2]?.toLowerCase() || "";
-    if (DANGEROUS_EXTENSIONS.includes(secondLastExt)) {
-      return "File has suspicious double extension";
-    }
+  // Check for dangerous extensions anywhere before the final extension.
+  // This catches both double and longer disguised chains (e.g. file.exe.safe.md).
+  const intermediateExtensions = parts.slice(1, -1).map((part) => part.toLowerCase());
+  if (intermediateExtensions.some((extension) => DANGEROUS_EXTENSIONS.includes(extension))) {
+    return "File has suspicious extension chain";
   }
 
   // Check if the actual extension is dangerous
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 1320f09737..a44b12236d 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -1219,6 +1219,9 @@ importers:
       vite-tsconfig-paths:
         specifier: 'catalog:'
         version: 5.1.4(typescript@5.8.3)(vite@8.0.16(@types/node@22.12.0)(esbuild@0.28.1)(jiti@2.7.0)(terser@5.43.1)(tsx@4.20.6)(yaml@2.8.3))
+      vitest:
+        specifier: 'catalog:'
+        version: 4.1.8(@opentelemetry/api@1.9.1)(@types/node@22.12.0)(@vitest/coverage-v8@4.1.8)(vite@8.0.16(@types/node@22.12.0)(esbuild@0.28.1)(jiti@2.7.0)(terser@5.43.1)(tsx@4.20.6)(yaml@2.8.3))
 
   packages/codemods:
     devDependencies:
@@ -1664,6 +1667,9 @@ importers:
       typescript:
         specifier: 5.8.3
         version: 5.8.3
+      vitest:
+        specifier: 'catalog:'
+        version: 4.1.8(@opentelemetry/api@1.9.1)(@types/node@22.12.0)(@vitest/coverage-v8@4.1.8)(vite@8.0.16(@types/node@22.12.0)(esbuild@0.28.1)(jiti@2.7.0)(terser@5.43.1)(tsx@4.20.6)(yaml@2.8.3))
 
   packages/shared-state:
     dependencies: