diff --git a/CHANGES.md b/CHANGES.md
index 7c73709d..a407ca4b 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -94,13 +94,24 @@ To be released.
         are removed; UnoCSS emits a single _src/public/uno.css_ whose
         URL is cache-busted by file mtime.
 
+ -  Fixed a bug where incoming ActivityPub posts with timestamps more than
+    12 hours in the future were accepted and stuck to the top of the
+    federated timeline, enabling timeline manipulation via forged timestamps.
+    Such posts are now silently ignored.  [[#67], [#466]]
+
+ -  Fixed a crash when persisting ActivityPub posts with a `published` date
+    before the Unix epoch (January 1, 1970), which caused `uuidv7()` to
+    receive a negative timestamp.  [[#67], [#466]]
+
  -  Upgraded Fedify to 2.2.0.
 
 [FEP-044f]: https://w3id.org/fep/044f
+[#67]: https://github.com/fedify-dev/hollo/issues/67
 [#457]: https://github.com/fedify-dev/hollo/pull/457
 [#458]: https://github.com/fedify-dev/hollo/pull/458
 [#459]: https://github.com/fedify-dev/hollo/pull/459
 [#460]: https://github.com/fedify-dev/hollo/pull/460
+[#466]: https://github.com/fedify-dev/hollo/pull/466
 
 
 Version 0.8.1
diff --git a/src/federation/inbox.ts b/src/federation/inbox.ts
index b91c87c2..16ada79d 100644
--- a/src/federation/inbox.ts
+++ b/src/federation/inbox.ts
@@ -974,8 +974,14 @@ export async function onPostUpdated(
       })
     : null;
 
-  // Persist the updated post
-  await persistPost(db, object, ctx.origin, getPersistOptions(ctx));
+  // Persist the updated post; null means the post was rejected (e.g. future timestamp)
+  const updatedPost = await persistPost(
+    db,
+    object,
+    ctx.origin,
+    getPersistOptions(ctx),
+  );
+  if (updatedPost == null) return;
 
   // Create quoted_update notifications for users who quoted this post
   if (existingPost != null) {
diff --git a/src/federation/post.test.ts b/src/federation/post.test.ts
index 7ec9720e..9b00fa90 100644
--- a/src/federation/post.test.ts
+++ b/src/federation/post.test.ts
@@ -17,6 +17,7 @@ import { createAccount } from "../../tests/helpers/oauth";
 import db from "../db";
 import { accounts, follows, instances, posts, timelinePosts } from "../schema";
 import type { Uuid } from "../uuid";
+import { toTemporalInstant } from "./date";
 import { onPostShared } from "./inbox";
 import { persistPost, persistSharingPost, toObject } from "./post";
 
@@ -381,6 +382,102 @@ describe("persistPost", () => {
     expect(post?.repliesCount).toBe(3);
     expect(jobs.map((job) => job.repliesIri)).toEqual([repliesIri]);
   });
+
+  it("ignores posts with a published date more than 12 hours in the future", async () => {
+    expect.assertions(3);
+    const author = await seedRemoteAccount("author");
+    const futureDate = new Date(Date.now() + 13 * 60 * 60 * 1000);
+    const iri = "https://remote.test/@author/posts/future";
+
+    const result = await persistPost(
+      db,
+      new Note({
+        id: new URL(iri),
+        attribution: createPerson(author),
+        content: "<p>From the future</p>",
+        to: PUBLIC_COLLECTION,
+        published: toTemporalInstant(futureDate),
+      }),
+      "https://hollo.test",
+      { account: author },
+    );
+    const row = await db.query.posts.findFirst({ where: eq(posts.iri, iri) });
+    const timelineRows = await db.query.timelinePosts.findMany();
+
+    expect(result).toBeNull();
+    expect(row).toBeUndefined();
+    expect(timelineRows).toHaveLength(0);
+  });
+
+  it("ignores posts with an updated date more than 12 hours in the future", async () => {
+    expect.assertions(3);
+    const author = await seedRemoteAccount("author");
+    const futureDate = new Date(Date.now() + 13 * 60 * 60 * 1000);
+    const iri = "https://remote.test/@author/posts/future-updated";
+
+    const result = await persistPost(
+      db,
+      new Note({
+        id: new URL(iri),
+        attribution: createPerson(author),
+        content: "<p>Updated in the future</p>",
+        to: PUBLIC_COLLECTION,
+        updated: toTemporalInstant(futureDate),
+      }),
+      "https://hollo.test",
+      { account: author },
+    );
+    const row = await db.query.posts.findFirst({ where: eq(posts.iri, iri) });
+    const timelineRows = await db.query.timelinePosts.findMany();
+
+    expect(result).toBeNull();
+    expect(row).toBeUndefined();
+    expect(timelineRows).toHaveLength(0);
+  });
+
+  it("accepts posts with a published date slightly in the future (within 12 hours)", async () => {
+    expect.assertions(1);
+    const author = await seedRemoteAccount("author");
+    const slightlyFutureDate = new Date(Date.now() + 11 * 60 * 60 * 1000);
+
+    const result = await persistPost(
+      db,
+      new Note({
+        id: new URL("https://remote.test/@author/posts/near-future"),
+        attribution: createPerson(author),
+        content: "<p>Slightly future</p>",
+        to: PUBLIC_COLLECTION,
+        published: toTemporalInstant(slightlyFutureDate),
+      }),
+      "https://hollo.test",
+      { account: author },
+    );
+
+    expect(result).not.toBeNull();
+  });
+
+  it("accepts posts with a pre-epoch timestamp without crashing", async () => {
+    expect.assertions(2);
+    const author = await seedRemoteAccount("author");
+    // 1963-11-22, before Unix epoch (1970-01-01)
+    const preEpochDate = new Date("1963-11-22T12:30:00Z");
+
+    const result = await persistPost(
+      db,
+      new Note({
+        id: new URL("https://remote.test/@author/posts/old-post"),
+        attribution: createPerson(author),
+        content: "<p>A very old post</p>",
+        to: PUBLIC_COLLECTION,
+        published: toTemporalInstant(preEpochDate),
+      }),
+      "https://hollo.test",
+      { account: author },
+    );
+
+    expect(result).not.toBeNull();
+    expect(result?.published).toEqual(preEpochDate);
+  });
 });
 
 describe("toObject", () => {
diff --git a/src/federation/post.ts b/src/federation/post.ts
index eb25e04b..837c7b0e 100644
--- a/src/federation/post.ts
+++ b/src/federation/post.ts
@@ -187,6 +187,21 @@ export async function persistPost(
   if (existingPost != null && existingPost.account.owner != null) {
     return existingPost;
   }
+  const publishedRaw = toDate(object.published);
+  const updatedRaw = toDate(object.updated);
+  const now = Date.now();
+  const twelveHoursMs = 12 * 60 * 60 * 1000;
+  if (
+    (publishedRaw != null && +publishedRaw > now + twelveHoursMs) ||
+    (updatedRaw != null && +updatedRaw > now + twelveHoursMs)
+  ) {
+    logger.debug(
+      "Ignoring post {iri} with a timestamp too far in the future: " +
+        "published={published}, updated={updated}",
+      { iri: object.id.href, published: publishedRaw, updated: updatedRaw },
+    );
+    return null;
+  }
   const actor = await object.getAttribution(options);
   logger.debug("Fetched actor: {actor}", { actor });
   if (!isActor(actor)) return null;
@@ -325,8 +340,8 @@ export async function persistPost(
   const preservedQuoteAuthorizationIri =
     quoteAuthorizationIri ??
     (preserveAcceptedQuote ? existingPost.quoteAuthorizationIri : null);
-  const published = toDate(object.published);
-  const updated = toDate(object.updated) ?? published ?? new Date();
+  const published = publishedRaw;
+  const updated = updatedRaw ?? published ?? new Date();
   const values = {
     type:
       object instanceof Question
@@ -380,7 +395,7 @@ export async function persistPost(
     .values({
       ...values,
       repliesCount: existingPost?.repliesCount ?? 0,
-      id: uuidv7(+(published ?? updated)),
+      id: uuidv7(Math.max(0, +(published ?? updated))),
       iri: object.id.href,
     })
     .onConflictDoUpdate({