From 5321f8124a9edfa4bc43006d64957f3b48d03c63 Mon Sep 17 00:00:00 2001
From: Cody Henthorne <cody@signal.org>
Date: Mon, 18 May 2026 15:37:22 -0400
Subject: [PATCH] Add additional download checks to long message text
 attachments.

---
 .../securesms/jobs/AttachmentDownloadJob.kt            |  6 ++++++
 .../org/thoughtcrime/securesms/util/AttachmentUtil.kt  |  2 +-
 .../thoughtcrime/securesms/util/AttachmentUtilTest.kt  | 10 ++++++++--
 3 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/app/src/main/java/org/thoughtcrime/securesms/jobs/AttachmentDownloadJob.kt b/app/src/main/java/org/thoughtcrime/securesms/jobs/AttachmentDownloadJob.kt
index 9e4c92d0c2..d136b62177 100644
--- a/app/src/main/java/org/thoughtcrime/securesms/jobs/AttachmentDownloadJob.kt
+++ b/app/src/main/java/org/thoughtcrime/securesms/jobs/AttachmentDownloadJob.kt
@@ -38,6 +38,8 @@ import org.thoughtcrime.securesms.notifications.v2.ConversationId.Companion.forC
 import org.thoughtcrime.securesms.s3.S3
 import org.thoughtcrime.securesms.transport.RetryLaterException
 import org.thoughtcrime.securesms.util.AttachmentUtil
+import org.thoughtcrime.securesms.util.MediaUtil
+import org.thoughtcrime.securesms.util.MessageUtil
 import org.thoughtcrime.securesms.util.RemoteConfig
 import org.whispersystems.signalservice.api.crypto.AttachmentCipherInputStream.IntegrityCheck
 import org.whispersystems.signalservice.api.crypto.AttachmentCipherStreamUtil
@@ -301,6 +303,10 @@ class AttachmentDownloadJob private constructor(
         throw MmsException("[$attachmentId] Attachment too large, failing download")
       }
 
+      if (MediaUtil.isLongTextType(attachment.contentType) && attachment.size > MessageUtil.MAX_TOTAL_BODY_SIZE_BYTES) {
+        throw InvalidAttachmentException("[$attachmentId] Long-text attachment exceeds ${MessageUtil.MAX_TOTAL_BODY_SIZE_BYTES} byte cap, declared size: ${attachment.size}")
+      }
+
       val pointer = createAttachmentPointer(attachment)
 
       val progressListener = object : SignalServiceAttachment.ProgressListener {
diff --git a/app/src/main/java/org/thoughtcrime/securesms/util/AttachmentUtil.kt b/app/src/main/java/org/thoughtcrime/securesms/util/AttachmentUtil.kt
index 629d139c6f..e00447db58 100644
--- a/app/src/main/java/org/thoughtcrime/securesms/util/AttachmentUtil.kt
+++ b/app/src/main/java/org/thoughtcrime/securesms/util/AttachmentUtil.kt
@@ -73,7 +73,7 @@ object AttachmentUtil {
     val contentType = attachment.contentType
 
     return when {
-      MediaUtil.isLongTextType(contentType) -> true
+      MediaUtil.isLongTextType(contentType) -> attachment.size <= MessageUtil.MAX_TOTAL_BODY_SIZE_BYTES
       attachment.isSticker -> ciphertextSize <= SMALL_ATTACHMENT_SIZE || allowedForType(allowedTypes, "image", "sticker")
       attachment.voiceNote -> ciphertextSize <= SMALL_ATTACHMENT_SIZE || allowedForType(allowedTypes, "audio", "voice message")
       attachment.videoGif -> allowedForType(allowedTypes, "image", "video gif")
diff --git a/app/src/test/java/org/thoughtcrime/securesms/util/AttachmentUtilTest.kt b/app/src/test/java/org/thoughtcrime/securesms/util/AttachmentUtilTest.kt
index 141133fd8e..af5e212d15 100644
--- a/app/src/test/java/org/thoughtcrime/securesms/util/AttachmentUtilTest.kt
+++ b/app/src/test/java/org/thoughtcrime/securesms/util/AttachmentUtilTest.kt
@@ -210,11 +210,17 @@ class AttachmentUtilTest {
   }
 
   @Test
-  fun `long text always permitted`() {
-    val attachment = attachment(contentType = "text/x-signal-plain")
+  fun `long text within 64 KiB cap permitted`() {
+    val attachment = attachment(size = MessageUtil.MAX_TOTAL_BODY_SIZE_BYTES.toLong(), contentType = "text/x-signal-plain")
     assertTrue(AttachmentUtil.isAutoDownloadPermitted(context, attachment))
   }
 
+  @Test
+  fun `long text exceeding 64 KiB cap rejected`() {
+    val attachment = attachment(size = MessageUtil.MAX_TOTAL_BODY_SIZE_BYTES.toLong() + 1, contentType = "text/x-signal-plain")
+    assertFalse(AttachmentUtil.isAutoDownloadPermitted(context, attachment))
+  }
+
   @Test
   fun `small sticker always permitted regardless of allowed types or in-call`() {
     val attachment = attachment(size = 50L * 1024, isSticker = true, contentType = "image/webp")