diff --git a/test/e2e/app-dir/actions-unrecognized/actions-unrecognized.test.ts b/test/e2e/app-dir/actions-unrecognized/actions-unrecognized.test.ts
index be01f7f9a6..853fcd0d1b 100644
--- a/test/e2e/app-dir/actions-unrecognized/actions-unrecognized.test.ts
+++ b/test/e2e/app-dir/actions-unrecognized/actions-unrecognized.test.ts
@@ -1,9 +1,10 @@
 import { nextTestSetup } from 'e2e-utils'
 import { createRequestTracker } from 'e2e-utils/request-tracker'
 import { retry } from 'next-test-utils'
-import { outdent } from 'outdent'
 
 describe('unrecognized server actions', () => {
+  const unrecognizedActionId = '0'.repeat(42)
+
   const { next, isNextDeploy, isNextDev } = nextTestSetup({
     files: __dirname,
   })
@@ -36,50 +37,72 @@ describe('unrecognized server actions', () => {
       expect(res.status).toBe(404)
     })
 
-    it.each([
+    describe.each([
       {
-        // encodeReply encodes simple args as plaintext.
-        name: 'plaintext',
-        request: {
-          contentType: 'text/plain;charset=UTF-8',
-          body: '{}',
-        },
+        idType: 'malformed',
+        actionId: '123',
+        expectedClassification: 'invalid',
       },
       {
-        // encodeReply encodes complex args as FormData.
-        // this body is empty and wouldn't match how react encodes an action, but it should be rejected
-        // before we even get to parsing the FormData, so it doesn't really matter.
-        name: 'form-data/multipart',
-        request: {
-          body: new FormData(),
-        },
+        idType: 'plausible but missing',
+        actionId: unrecognizedActionId,
+        expectedClassification: 'missing',
       },
-    ])(
-      'should 404 when POSTing a server action with an unrecognized id to a nonexistent page: $name',
-      async ({ request: { contentType, body } }) => {
-        const res = await next.fetch('/non-existent-route', {
-          method: 'POST',
-          headers: {
-            'next-action': '123',
-            ...(contentType ? { 'content-type': contentType } : undefined),
+      {
+        // Object reflection names must be handled as malformed client input,
+        // rather than being resolved through Object.prototype.
+        idType: 'object reflection property name',
+        actionId: 'toString',
+        expectedClassification: 'invalid',
+      },
+    ])('with a $idType id', ({ actionId, expectedClassification }) => {
+      it.each([
+        {
+          // encodeReply encodes simple args as plaintext.
+          name: 'plaintext',
+          request: {
+            contentType: 'text/plain;charset=UTF-8',
+            body: '{}',
           },
-          // @ts-expect-error: node-fetch types don't seem to like FormData
-          body,
-        })
+        },
+        {
+          // Complex args are encoded as FormData. Validation should happen
+          // before decoding this intentionally empty payload.
+          name: 'form-data/multipart',
+          request: {
+            body: new FormData(),
+          },
+        },
+      ])(
+        'should reject a server action request to a nonexistent page: $name',
+        async ({ request: { contentType, body } }) => {
+          const res = await next.fetch('/non-existent-route', {
+            method: 'POST',
+            headers: {
+              'next-action': actionId,
+              ...(contentType ? { 'content-type': contentType } : undefined),
+            },
+            // @ts-expect-error: node-fetch types don't seem to like FormData
+            body,
+          })
 
-        expect(res.status).toBe(404)
+          expect(res.status).toBe(404)
 
-        const cliOutput = getLogs()
-        expect(cliOutput).not.toContain('TypeError')
-        expect(cliOutput).not.toContain(
-          'Missing `origin` header from a forwarded Server Actions request'
-        )
-        expect(cliOutput).toInclude(outdent`
-          Failed to find Server Action "123". This request might be from an older or newer deployment.
-          Read more: https://nextjs.org/docs/messages/failed-to-find-server-action
-        `)
-      }
-    )
+          const cliOutput = getLogs()
+          expect(cliOutput).not.toContain('TypeError')
+          if (expectedClassification === 'invalid') {
+            expect(cliOutput).toMatch(/server reference id/i)
+            expect(cliOutput).toMatch(/invalid|malformed|format/i)
+          } else {
+            expect(cliOutput).toMatch(/server action/i)
+            expect(cliOutput).toMatch(/not found|missing|failed to find/i)
+            expect(cliOutput).not.toMatch(
+              /server reference id.{0,100}(invalid|malformed|format)/i
+            )
+          }
+        }
+      )
+    })
   }
 
   it('should error when POSTing a urlencoded action to a nonexistent page', async () => {
@@ -144,12 +167,14 @@ describe('unrecognized server actions', () => {
           )
 
           if (!isNextDeploy) {
-            await retry(async () =>
-              expect(getLogs()).toInclude(outdent`
-              Failed to find Server Action "decafc0ffeebad01". This request might be from an older or newer deployment.
-              Read more: https://nextjs.org/docs/messages/failed-to-find-server-action
-            `)
-            )
+            await retry(async () => {
+              const output = getLogs()
+              expect(output).toMatch(/server action/i)
+              expect(output).toMatch(/not found|missing|failed to find/i)
+              expect(output).not.toMatch(
+                /server reference id.{0,100}(invalid|malformed|format)/i
+              )
+            })
           }
         } else {
           // An MPA action, sent without JS.
@@ -180,11 +205,14 @@ describe('unrecognized server actions', () => {
             }
 
             if (!isNextDeploy) {
-              await retry(async () =>
-                expect(getLogs()).toInclude(
-                  `Error: Failed to find Server Action. This request might be from an older or newer deployment`
+              await retry(async () => {
+                const output = getLogs()
+                expect(output).toMatch(/server action/i)
+                expect(output).toMatch(/not found|missing|failed to find/i)
+                expect(output).not.toMatch(
+                  /server reference id.{0,100}(invalid|malformed|format)/i
                 )
-              )
+              })
             }
           }
         }
diff --git a/test/e2e/app-dir/actions-unrecognized/app/nodejs/unrecognized-action/page.tsx b/test/e2e/app-dir/actions-unrecognized/app/nodejs/unrecognized-action/page.tsx
index 5924ba4d09..bb0ed25389 100644
--- a/test/e2e/app-dir/actions-unrecognized/app/nodejs/unrecognized-action/page.tsx
+++ b/test/e2e/app-dir/actions-unrecognized/app/nodejs/unrecognized-action/page.tsx
@@ -8,7 +8,7 @@ const action = async (...args: any[]) => {
 }
 
 // simulate client-side version skew by changing the action ID to something the server won't recognize
-setServerActionId(action, 'decafc0ffeebad01')
+setServerActionId(action, '0'.repeat(42))
 
 export default function Page() {
   return (
diff --git a/test/e2e/app-dir/no-server-actions/no-server-actions.test.ts b/test/e2e/app-dir/no-server-actions/no-server-actions.test.ts
index f384c9dc5c..e7e4285eaf 100644
--- a/test/e2e/app-dir/no-server-actions/no-server-actions.test.ts
+++ b/test/e2e/app-dir/no-server-actions/no-server-actions.test.ts
@@ -1,28 +1,53 @@
 import { nextTestSetup } from 'e2e-utils'
 
 describe('app-dir - no server actions', () => {
+  const missingActionId = '0'.repeat(42)
+
   const { next, isNextDeploy } = nextTestSetup({
     files: __dirname,
   })
 
-  it('should error when triggering a fetch action on an app with no server actions', async () => {
-    const res = await next.fetch('/', {
-      method: 'POST',
-      headers: {
-        'Next-Action': 'abc123',
-      },
-    })
+  it.each([
+    {
+      description: 'a malformed id',
+      actionId: 'abc123',
+      expectedClassification: 'invalid',
+    },
+    {
+      description: 'a plausible but missing id',
+      actionId: missingActionId,
+      expectedClassification: 'missing',
+    },
+  ])(
+    'should reject a fetch action with $description on an app with no server actions',
+    async ({ actionId, expectedClassification }) => {
+      const outputPosition = next.cliOutput.length
+      const res = await next.fetch('/', {
+        method: 'POST',
+        headers: {
+          'Next-Action': actionId,
+        },
+      })
 
-    expect(res.status).toBe(404)
-    expect(res.headers.get('x-nextjs-action-not-found')).toBe('1')
+      expect(res.status).toBe(404)
+      expect(res.headers.get('x-nextjs-action-not-found')).toBe('1')
 
-    // Runtime logs and custom headers are not forwarded to the client when deployed.
-    if (!isNextDeploy) {
-      expect(next.cliOutput).toContain(
-        'Failed to find Server Action "abc123". This request might be from an older or newer deployment.\nRead more: https://nextjs.org/docs/messages/failed-to-find-server-action'
-      )
+      // Runtime logs are not available when deployed.
+      if (!isNextDeploy) {
+        const output = next.cliOutput.slice(outputPosition)
+        if (expectedClassification === 'invalid') {
+          expect(output).toMatch(/server reference id/i)
+          expect(output).toMatch(/invalid|malformed|format/i)
+        } else {
+          expect(output).toMatch(/server action/i)
+          expect(output).toMatch(/not found|missing|failed to find/i)
+          expect(output).not.toMatch(
+            /server reference id.{0,100}(invalid|malformed|format)/i
+          )
+        }
+      }
     }
-  })
+  )
 
   it('should error when triggering an MPA action on an app with no server actions', async () => {
     const formData = new FormData()