diff --git a/x-pack/plugins/security_solution/server/endpoint/services/artifacts/manifest_manager/manifest_manager.mock.ts b/x-pack/plugins/security_solution/server/endpoint/services/artifacts/manifest_manager/manifest_manager.mock.ts
index 592ffb0eae62a..34e18c5fe85fc 100644
--- a/x-pack/plugins/security_solution/server/endpoint/services/artifacts/manifest_manager/manifest_manager.mock.ts
+++ b/x-pack/plugins/security_solution/server/endpoint/services/artifacts/manifest_manager/manifest_manager.mock.ts
@@ -8,6 +8,7 @@ import { savedObjectsClientMock, loggingSystemMock } from 'src/core/server/mocks
 import { Logger } from 'src/core/server';
 import { PackageConfigServiceInterface } from '../../../../../../ingest_manager/server';
 import { createPackageConfigServiceMock } from '../../../../../../ingest_manager/server/mocks';
+import { ExceptionListClient } from '../../../../../../lists/server';
 import { listMock } from '../../../../../../lists/server/mocks';
 import LRU from 'lru-cache';
 import { getArtifactClientMock } from '../artifact_client.mock';
@@ -23,22 +24,29 @@ import {
 
 export enum ManifestManagerMockType {
   InitialSystemState,
+  ListClientPromiseRejection,
   NormalFlow,
 }
 
 export const getManifestManagerMock = (opts?: {
   mockType?: ManifestManagerMockType;
   cache?: LRU<string, Buffer>;
+  exceptionListClient?: ExceptionListClient;
   packageConfigService?: jest.Mocked<PackageConfigServiceInterface>;
   savedObjectsClient?: ReturnType<typeof savedObjectsClientMock.create>;
 }): ManifestManager => {
   let cache = new LRU<string, Buffer>({ max: 10, maxAge: 1000 * 60 * 60 });
-  if (opts?.cache !== undefined) {
+  if (opts?.cache != null) {
     cache = opts.cache;
   }
 
+  let exceptionListClient = listMock.getExceptionListClient();
+  if (opts?.exceptionListClient != null) {
+    exceptionListClient = opts.exceptionListClient;
+  }
+
   let packageConfigService = createPackageConfigServiceMock();
-  if (opts?.packageConfigService !== undefined) {
+  if (opts?.packageConfigService != null) {
     packageConfigService = opts.packageConfigService;
   }
   packageConfigService.list = jest.fn().mockResolvedValue({
@@ -51,7 +59,7 @@ export const getManifestManagerMock = (opts?: {
   });
 
   let savedObjectsClient = savedObjectsClientMock.create();
-  if (opts?.savedObjectsClient !== undefined) {
+  if (opts?.savedObjectsClient != null) {
     savedObjectsClient = opts.savedObjectsClient;
   }
 
@@ -61,6 +69,11 @@ export const getManifestManagerMock = (opts?: {
       switch (mockType) {
         case ManifestManagerMockType.InitialSystemState:
           return getEmptyMockArtifacts();
+        case ManifestManagerMockType.ListClientPromiseRejection:
+          exceptionListClient.findExceptionListItem = jest
+            .fn()
+            .mockRejectedValue(new Error('unexpected thing happened'));
+          return super.buildExceptionListArtifacts('v1');
         case ManifestManagerMockType.NormalFlow:
           return getMockArtifactsWithDiff();
       }
@@ -85,7 +98,7 @@ export const getManifestManagerMock = (opts?: {
     artifactClient: getArtifactClientMock(savedObjectsClient),
     cache,
     packageConfigService,
-    exceptionListClient: listMock.getExceptionListClient(),
+    exceptionListClient,
     logger: loggingSystemMock.create().get() as jest.Mocked<Logger>,
     savedObjectsClient,
   });
diff --git a/x-pack/plugins/security_solution/server/endpoint/services/artifacts/manifest_manager/manifest_manager.test.ts b/x-pack/plugins/security_solution/server/endpoint/services/artifacts/manifest_manager/manifest_manager.test.ts
index d99d6a959d7aa..8e0d55104fb7c 100644
--- a/x-pack/plugins/security_solution/server/endpoint/services/artifacts/manifest_manager/manifest_manager.test.ts
+++ b/x-pack/plugins/security_solution/server/endpoint/services/artifacts/manifest_manager/manifest_manager.test.ts
@@ -9,7 +9,7 @@ import { savedObjectsClientMock } from 'src/core/server/mocks';
 import { createPackageConfigServiceMock } from '../../../../../../ingest_manager/server/mocks';
 import { ArtifactConstants, ManifestConstants, isCompleteArtifact } from '../../../lib/artifacts';
 
-import { getManifestManagerMock } from './manifest_manager.mock';
+import { getManifestManagerMock, ManifestManagerMockType } from './manifest_manager.mock';
 import LRU from 'lru-cache';
 
 describe('manifest_manager', () => {
@@ -204,5 +204,14 @@ describe('manifest_manager', () => {
         oldArtifactId
       );
     });
+
+    test('ManifestManager handles promise rejections when building artifacts', async () => {
+      // This test won't fail on an unhandled promise rejection, but it will cause
+      // an UnhandledPromiseRejectionWarning to be printed.
+      const manifestManager = getManifestManagerMock({
+        mockType: ManifestManagerMockType.ListClientPromiseRejection,
+      });
+      await expect(manifestManager.buildNewManifest()).rejects.toThrow();
+    });
   });
 });
diff --git a/x-pack/plugins/security_solution/server/endpoint/services/artifacts/manifest_manager/manifest_manager.ts b/x-pack/plugins/security_solution/server/endpoint/services/artifacts/manifest_manager/manifest_manager.ts
index b5f7b1384750f..1bc0e9564ee9e 100644
--- a/x-pack/plugins/security_solution/server/endpoint/services/artifacts/manifest_manager/manifest_manager.ts
+++ b/x-pack/plugins/security_solution/server/endpoint/services/artifacts/manifest_manager/manifest_manager.ts
@@ -82,18 +82,17 @@ export class ManifestManager {
   protected async buildExceptionListArtifacts(
     artifactSchemaVersion?: string
   ): Promise<InternalArtifactCompleteSchema[]> {
-    return ArtifactConstants.SUPPORTED_OPERATING_SYSTEMS.reduce<
-      Promise<InternalArtifactCompleteSchema[]>
-    >(async (acc, os) => {
+    const artifacts: InternalArtifactCompleteSchema[] = [];
+    for (const os of ArtifactConstants.SUPPORTED_OPERATING_SYSTEMS) {
       const exceptionList = await getFullEndpointExceptionList(
         this.exceptionListClient,
         os,
         artifactSchemaVersion ?? 'v1'
       );
-      const artifacts = await acc;
       const artifact = await buildArtifact(exceptionList, os, artifactSchemaVersion ?? 'v1');
-      return Promise.resolve([...artifacts, artifact]);
-    }, Promise.resolve([]));
+      artifacts.push(artifact);
+    }
+    return artifacts;
   }
 
   /**