From 5eac12188a848bc23f2f237a887be970e63d2083 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=EC=95=88=EB=AF=BC=EA=B8=B0?=
 <205003064+Sn0wyDay@users.noreply.github.com>
Date: Sun, 13 Sep 2026 02:05:53 +0900
Subject: [PATCH] Fix parsing of exact-length JSON with a UTF-8 BOM

---
 cJSON.c                |  2 +-
 tests/parse_examples.c | 13 +++++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/cJSON.c b/cJSON.c
index 88c2d95b..46f21d9b 100644
--- a/cJSON.c
+++ b/cJSON.c
@@ -1120,7 +1120,7 @@ static parse_buffer *skip_utf8_bom(parse_buffer * const buffer)
         return NULL;
     }
 
-    if (can_access_at_index(buffer, 4) && (strncmp((const char*)buffer_at_offset(buffer), "\xEF\xBB\xBF", 3) == 0))
+    if (can_access_at_index(buffer, 2) && (strncmp((const char*)buffer_at_offset(buffer), "\xEF\xBB\xBF", 3) == 0))
     {
         buffer->offset += 3;
     }
diff --git a/tests/parse_examples.c b/tests/parse_examples.c
index d35d6cfb..9df2ebd1 100644
--- a/tests/parse_examples.c
+++ b/tests/parse_examples.c
@@ -277,6 +277,18 @@ static void test15_should_not_heap_buffer_overflow(void)
     }
 }
 
+static void test16_should_parse_short_json_with_bom_without_null_termination(void)
+{
+    const char json[] = { (char)0xef, (char)0xbb, (char)0xbf, '0' };
+    cJSON *tree = cJSON_ParseWithLength(json, sizeof(json));
+
+    TEST_ASSERT_NOT_NULL_MESSAGE(tree, "Failed to parse valid short JSON with a UTF-8 BOM.");
+    TEST_ASSERT_TRUE(cJSON_IsNumber(tree));
+    TEST_ASSERT_EQUAL_DOUBLE(0, tree->valuedouble);
+
+    cJSON_Delete(tree);
+}
+
 int CJSON_CDECL main(void)
 {
     UNITY_BEGIN();
@@ -295,5 +307,6 @@ int CJSON_CDECL main(void)
     RUN_TEST(test13_should_be_parsed_without_null_termination);
     RUN_TEST(test14_should_not_be_parsed);
     RUN_TEST(test15_should_not_heap_buffer_overflow);
+    RUN_TEST(test16_should_parse_short_json_with_bom_without_null_termination);
     return UNITY_END();
 }