diff --git a/docs/testing.md b/docs/testing.md
index 0c59dc56cd..d9d4775d35 100644
--- a/docs/testing.md
+++ b/docs/testing.md
@@ -897,8 +897,13 @@ After import, deleting that source must preserve the captured database identity.
 Instruction inspection and containing-function lookup also agree across
 hexadecimal case, leading zeros, and encoded default address-space spellings.
 The same source-acquisition workflow exercises missing and directory-replaced
-inputs, plus real read-permission denial on a non-root host. Root runs report
-that permission-denial check as unverified. Filesystem integration separately checks selected-platform routing and exclusive creation.
+inputs, plus real read-permission denial on a host that enforces it. Permission
+fixtures must probe the relevant read, write or search operation before relying
+on POSIX mode bits: a non-root Linux process may bypass DAC through capabilities.
+`requirePermissionDenial` reports an explicit skip when the host permits the
+probe; it restores the probe's permissions before skipping. Such a skip leaves
+real permission coverage unverified. Filesystem integration separately checks
+selected-platform routing and exclusive creation.
 Namespace annotation probes compile a separate host C fixture with C++ ABI
 symbols, avoiding a C++ runtime prerequisite. Real Ghidra demangling supplies
 duplicate leaf names in two top-level namespaces and a nested namespace. The
diff --git a/src/application/environment/environmentBundleWrite.test.ts b/src/application/environment/environmentBundleWrite.test.ts
index 1e1ec5dd5e..5a10e337c9 100644
--- a/src/application/environment/environmentBundleWrite.test.ts
+++ b/src/application/environment/environmentBundleWrite.test.ts
@@ -1,3 +1,4 @@
+import { requirePermissionDenial } from "../../../tests/fixtures/permissionDenial.js";
 import {
   appendFile,
   chmod,
@@ -167,9 +168,10 @@ it("uses confirmed publication after the output owner's descriptor cleanup compl
   }
 });
 
-it.skipIf(process.platform === "win32" || process.getuid?.() === 0)(
+it.skipIf(process.platform === "win32")(
   "returns a tagged permission refusal for an existing read-only empty directory",
-  async () => {
+  async (context) => {
+    await requirePermissionDenial(context, "directory-write");
     const root = await createTestTempDirectory("rea-bundle-readonly-");
     const files = await writeEnvironmentServeFiles(root);
     const inputs = await readEnvironmentExportInputs(
@@ -200,9 +202,10 @@ it.skipIf(process.platform === "win32" || process.getuid?.() === 0)(
   },
 );
 
-it.skipIf(process.platform === "win32" || process.getuid?.() === 0)(
+it.skipIf(process.platform === "win32")(
   "names the nested path when write permission is lost after earlier files",
-  async () => {
+  async (context) => {
+    await requirePermissionDenial(context, "directory-write");
     const root = await createTestTempDirectory("rea-bundle-later-denied-");
     const files = await writeEnvironmentServeFiles(root);
     const inputs = await readEnvironmentExportInputs(
diff --git a/src/hopper/HopperMachOImage.test.ts b/src/hopper/HopperMachOImage.test.ts
index 0e509b5e58..3a90caa6c9 100644
--- a/src/hopper/HopperMachOImage.test.ts
+++ b/src/hopper/HopperMachOImage.test.ts
@@ -1,3 +1,4 @@
+import { requirePermissionDenial } from "../../tests/fixtures/permissionDenial.js";
 import { createHash } from "node:crypto";
 import {
   access,
@@ -129,9 +130,10 @@ const resolveHopperMachOImage = (
     resourceScope: inspectionResources.owner,
   });
 
-it.skipIf(process.platform === "win32" || process.getuid?.() === 0)(
+it.skipIf(process.platform === "win32")(
   "reports a FAT64 source that became unreadable as a host read denial",
-  async () => {
+  async (context) => {
+    await requirePermissionDenial(context, "file-read");
     const directory = await createTestTempDirectory("rea-hopper-fat64-");
     const path = join(directory, "universal");
     await writeFile(path, Buffer.alloc(64));
diff --git a/src/hopper/HopperTargetLease.test.ts b/src/hopper/HopperTargetLease.test.ts
index 3170d09d6f..59b68927a0 100644
--- a/src/hopper/HopperTargetLease.test.ts
+++ b/src/hopper/HopperTargetLease.test.ts
@@ -1,3 +1,4 @@
+import { requirePermissionDenial } from "../../tests/fixtures/permissionDenial.js";
 import { execFile } from "node:child_process";
 import { once } from "node:events";
 import {
@@ -75,9 +76,10 @@ describe.skipIf(process.platform === "win32")(
       expect((await lstat(alias)).isSymbolicLink()).toBe(true);
     });
 
-    it.skipIf(process.getuid?.() === 0)(
+    it.skipIf(process.platform === "win32")(
       "explains unreadable directory recovery without changing unverified permissions",
-      async () => {
+      async (context) => {
+        await requirePermissionDenial(context, "directory-read");
         const directory = await temporaryDirectory();
         await chmod(directory, 0o333);
         try {
diff --git a/src/ida/IdaWorkspaceOwnership.test.ts b/src/ida/IdaWorkspaceOwnership.test.ts
index c406dee7b3..d0e014fa3e 100644
--- a/src/ida/IdaWorkspaceOwnership.test.ts
+++ b/src/ida/IdaWorkspaceOwnership.test.ts
@@ -1,3 +1,4 @@
+import { requirePermissionDenial } from "../../tests/fixtures/permissionDenial.js";
 import { chmod, mkdir, readdir, realpath, rm, symlink } from "node:fs/promises";
 import { dirname, join } from "node:path";
 import { afterEach, describe, expect, it } from "vitest";
@@ -93,9 +94,10 @@ describe("IDA workspace ownership before input preparation", () => {
     expect(await readdir(root)).toEqual([]);
   });
 
-  it.skipIf(process.platform === "win32" || process.getuid?.() === 0)(
+  it.skipIf(process.platform === "win32")(
     "preserves the input identity failure and retries workspace removal after permission recovery",
-    async () => {
+    async (context) => {
+      await requirePermissionDenial(context, "directory-write");
       const { root, target } = await createIdaTarget();
       roots.push(root);
       const { client, producer } = clientFor(root, {
diff --git a/src/process/capture/FilesystemCoverage.test.ts b/src/process/capture/FilesystemCoverage.test.ts
index 6daf6572b2..f60eba8b1b 100644
--- a/src/process/capture/FilesystemCoverage.test.ts
+++ b/src/process/capture/FilesystemCoverage.test.ts
@@ -1,3 +1,4 @@
+import { requirePermissionDenial } from "../../../tests/fixtures/permissionDenial.js";
 import {
   chmod,
   mkdir,
@@ -104,9 +105,10 @@ it("distinguishes unavailable content hashes from completed path enumeration", a
   ).toMatchObject({ status: "deleted", before: { sha256: null }, after: null });
 });
 
-it.skipIf(process.platform === "win32" || process.getuid?.() === 0)(
+it.skipIf(process.platform === "win32")(
   "retains readable entries and marks an unreadable directory subtree unknown",
-  async () => {
+  async (context) => {
+    await requirePermissionDenial(context, "directory-read");
     const root = await createTestTempDirectory("rea-fs-unreadable-directory-");
     const visible = join(root, "a-visible.txt");
     const blocked = join(root, "z-blocked");
@@ -143,9 +145,10 @@ it.skipIf(process.platform === "win32" || process.getuid?.() === 0)(
   },
 );
 
-it.skipIf(process.platform === "win32" || process.getuid?.() === 0)(
+it.skipIf(process.platform === "win32")(
   "retains unreadable-file and sibling observations in a complete snapshot",
-  async () => {
+  async (context) => {
+    await requirePermissionDenial(context, "file-read");
     const root = await createTestTempDirectory("rea-fs-unreadable-file-");
     const unreadable = join(root, "unreadable.txt");
     const readable = join(root, "readable.txt");
@@ -398,9 +401,10 @@ it("preserves creation when the selected root was observed missing before captur
   ]);
 });
 
-it.skipIf(process.platform === "win32" || process.getuid?.() === 0)(
+it.skipIf(process.platform === "win32")(
   "rejects only selected roots that cannot be admitted before launch",
-  async () => {
+  async (context) => {
+    await requirePermissionDenial(context, "directory-search");
     const root = await createTestTempDirectory("rea-fs-root-admission-");
     await writeFile(join(root, "file"), "regular file");
     await mkdir(join(root, "denied"));
@@ -466,9 +470,10 @@ it.skipIf(process.platform === "win32" || process.getuid?.() === 0)(
   },
 );
 
-it.skipIf(process.platform === "win32" || process.getuid?.() === 0)(
+it.skipIf(process.platform === "win32")(
   "records an unsearchable directory's children as omitted rather than failing",
-  async () => {
+  async (context) => {
+    await requirePermissionDenial(context, "directory-search");
     const root = await createTestTempDirectory("rea-fs-unsearchable-");
     const listed = join(root, "listed");
     await mkdir(listed);
diff --git a/tests/fixtures/permissionDenial.ts b/tests/fixtures/permissionDenial.ts
new file mode 100644
index 0000000000..23e7fd8fa2
--- /dev/null
+++ b/tests/fixtures/permissionDenial.ts
@@ -0,0 +1,63 @@
+import {
+  chmod,
+  mkdir,
+  readFile,
+  readdir,
+  stat,
+  writeFile,
+} from "node:fs/promises";
+import { join } from "node:path";
+import type { TestContext } from "vitest";
+
+import { createTestTempDirectory } from "./temporaryDirectory.js";
+
+type PermissionOperation =
+  | "file-read"
+  | "directory-read"
+  | "directory-write"
+  | "directory-search";
+
+/** Probe actual DAC enforcement; UID alone does not account for Linux capabilities. */
+export const requirePermissionDenial = async (
+  context: Pick<TestContext, "skip">,
+  operation: PermissionOperation,
+): Promise<void> => {
+  if (process.platform === "win32")
+    context.skip("POSIX mode denial is unavailable on Windows");
+  const root = await createTestTempDirectory("rea-permission-probe-");
+  const directory = join(root, "directory");
+  const file = join(directory, "file");
+  await mkdir(directory);
+  await writeFile(file, "probe");
+  let denied = false;
+  try {
+    if (operation === "file-read") {
+      await chmod(file, 0);
+      await readFile(file);
+    } else if (operation === "directory-read") {
+      await chmod(directory, 0o333);
+      await readdir(directory);
+    } else if (operation === "directory-write") {
+      await chmod(directory, 0o500);
+      await writeFile(join(directory, "created"), "probe");
+    } else {
+      await chmod(directory, 0o444);
+      await stat(file);
+    }
+  } catch (cause) {
+    if (
+      !(cause instanceof Error) ||
+      !("code" in cause) ||
+      cause.code !== "EACCES"
+    )
+      throw cause;
+    denied = true;
+  } finally {
+    await chmod(directory, 0o700);
+    await chmod(file, 0o600);
+  }
+  if (!denied)
+    context.skip(
+      `Host bypasses POSIX ${operation} denial; real permission coverage is unverified`,
+    );
+};