From 7e386534920a81ccc31807279920a3bf874d4395 Mon Sep 17 00:00:00 2001
From: Timothy Flynn <trflynn89@pm.me>
Date: Sun, 24 Mar 2024 08:59:00 -0400
Subject: [PATCH] AK: Reject invalid Base64 encoded string lengths

---
 AK/Base64.cpp           | 3 +++
 Tests/AK/TestBase64.cpp | 5 +++++
 2 files changed, 8 insertions(+)

diff --git a/AK/Base64.cpp b/AK/Base64.cpp
index 058fd808a69..a8fa7f8c8b3 100644
--- a/AK/Base64.cpp
+++ b/AK/Base64.cpp
@@ -34,6 +34,9 @@ static ErrorOr<ByteBuffer> decode_base64_impl(StringView input, ReadonlySpan<i16
 {
     input = input.trim_whitespace();
 
+    if (input.length() % 4 != 0)
+        return Error::from_string_literal("Invalid length of Base64 encoded string");
+
     auto get = [&](size_t offset, bool* is_padding) -> ErrorOr<u8> {
         if (offset >= input.length())
             return 0;
diff --git a/Tests/AK/TestBase64.cpp b/Tests/AK/TestBase64.cpp
index fb410113feb..a04a0c8dd5b 100644
--- a/Tests/AK/TestBase64.cpp
+++ b/Tests/AK/TestBase64.cpp
@@ -40,6 +40,11 @@ TEST_CASE(test_decode_invalid)
 
     EXPECT(decode_base64("aGVsbG8_d29ybGQ="sv).is_error());
     EXPECT(decode_base64url("aGVsbG8/d29ybGQ="sv).is_error());
+
+    EXPECT(decode_base64("Y"sv).is_error());
+    EXPECT(decode_base64("YQ"sv).is_error());
+    EXPECT(decode_base64("YQ="sv).is_error());
+    EXPECT(decode_base64("PHN2ZyB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciIHdpZHRoPSIxMC42MDUiIGhlaWdodD0iMTUuNTU1Ij48cGF0aCBmaWxsPSIjODg5IiBkPSJtMi44MjggMTUuNTU1IDcuNzc3LTcuNzc5TDIuODI4IDAgMCAyLjgyOGw0Ljk0OSA0Ljk0OEwwIDEyLjcyN2wyLjgyOCAyLjgyOHoiLz48L3N2Zz4"sv).is_error());
 }
 
 TEST_CASE(test_decode_only_padding)