From 4d4181246e3e45e7ea4cb115b31cf66aa5d2b6b7 Mon Sep 17 00:00:00 2001
From: sahilkamate03 <45514385+sahilkamate03@users.noreply.github.com>
Date: Wed, 29 Jul 2026 13:25:57 +0530
Subject: [PATCH] Fix CBOR tag handlers not recognizing tags 0-5 and 21-23

The tagged-item switch in binary_reader::parse_cbor_internal() only handled
head bytes 0xC6-0xD4 and 0xD8-0xDB. Bytes 0xC0-0xC5 (tags 0-5: date/time,
epoch, bignum, decimal, bigfloat) and 0xD5-0xD7 (tags 21-23: base64url,
base64, base16 conversion hints) fell through to the default case and were
reported as invalid bytes, even under cbor_tag_handler_t::ignore and ::store,
despite being valid CBOR major-type-6 tags per RFC 8949.

Add the missing case labels so the full 0xC0-0xDB range is handled
uniformly. Extend the "Tagged values" test in unit-cbor.cpp to cover
0xC0-0xD7, and update the CBOR docs to state the corrected tag range.

Fixes #5315

Signed-off-by: sahilkamate03 <45514385+sahilkamate03@users.noreply.github.com>
---
 docs/mkdocs/docs/features/binary_formats/cbor.md |  2 +-
 include/nlohmann/detail/input/binary_reader.hpp  | 11 ++++++++++-
 single_include/nlohmann/json.hpp                 | 11 ++++++++++-
 tests/src/unit-cbor.cpp                          |  6 ++++--
 4 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/docs/mkdocs/docs/features/binary_formats/cbor.md b/docs/mkdocs/docs/features/binary_formats/cbor.md
index d385c2a4c2..5bf9f912d3 100644
--- a/docs/mkdocs/docs/features/binary_formats/cbor.md
+++ b/docs/mkdocs/docs/features/binary_formats/cbor.md
@@ -181,7 +181,7 @@ The library maps CBOR types to JSON value types as follows:
 
 !!! warning "Tagged items"
 
-    Tagged items will throw a parse error by default. They can be ignored by passing `cbor_tag_handler_t::ignore` to function `from_cbor`. They can be stored by passing `cbor_tag_handler_t::store` to function `from_cbor`.
+    Tagged items (`0xC0`..`0xDB`) will throw a parse error by default. They can be ignored by passing `cbor_tag_handler_t::ignore` to function `from_cbor`. They can be stored by passing `cbor_tag_handler_t::store` to function `from_cbor`.
 
 ??? example
 
diff --git a/include/nlohmann/detail/input/binary_reader.hpp b/include/nlohmann/detail/input/binary_reader.hpp
index ad862827d0..009db9bcbc 100644
--- a/include/nlohmann/detail/input/binary_reader.hpp
+++ b/include/nlohmann/detail/input/binary_reader.hpp
@@ -760,7 +760,13 @@ class binary_reader
             case 0xBF: // map (indefinite length)
                 return get_cbor_object(detail::unknown_size(), tag_handler);
 
-            case 0xC6: // tagged item
+            case 0xC0: // tagged item
+            case 0xC1:
+            case 0xC2:
+            case 0xC3:
+            case 0xC4:
+            case 0xC5:
+            case 0xC6:
             case 0xC7:
             case 0xC8:
             case 0xC9:
@@ -775,6 +781,9 @@ class binary_reader
             case 0xD2:
             case 0xD3:
             case 0xD4:
+            case 0xD5:
+            case 0xD6:
+            case 0xD7:
             case 0xD8: // tagged item (1 byte follows)
             case 0xD9: // tagged item (2 bytes follow)
             case 0xDA: // tagged item (4 bytes follow)
diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
index 5ead5275a3..25698864a8 100644
--- a/single_include/nlohmann/json.hpp
+++ b/single_include/nlohmann/json.hpp
@@ -11309,7 +11309,13 @@ class binary_reader
             case 0xBF: // map (indefinite length)
                 return get_cbor_object(detail::unknown_size(), tag_handler);
 
-            case 0xC6: // tagged item
+            case 0xC0: // tagged item
+            case 0xC1:
+            case 0xC2:
+            case 0xC3:
+            case 0xC4:
+            case 0xC5:
+            case 0xC6:
             case 0xC7:
             case 0xC8:
             case 0xC9:
@@ -11324,6 +11330,9 @@ class binary_reader
             case 0xD2:
             case 0xD3:
             case 0xD4:
+            case 0xD5:
+            case 0xD6:
+            case 0xD7:
             case 0xD8: // tagged item (1 byte follows)
             case 0xD9: // tagged item (2 bytes follow)
             case 0xDA: // tagged item (4 bytes follow)
diff --git a/tests/src/unit-cbor.cpp b/tests/src/unit-cbor.cpp
index af73642997..fdaab4e828 100644
--- a/tests/src/unit-cbor.cpp
+++ b/tests/src/unit-cbor.cpp
@@ -2529,11 +2529,13 @@ TEST_CASE("Tagged values")
     const json j = "s";
     auto v = json::to_cbor(j);
 
-    SECTION("0xC6..0xD4")
+    SECTION("0xC0..0xD7")
     {
         for (const auto b : std::vector<std::uint8_t>
     {
-        0xC6, 0xC7, 0xC8, 0xC9, 0xCA, 0xCB, 0xCC, 0xCD, 0xCE, 0xCF, 0xD0, 0xD1, 0xD2, 0xD3, 0xD4
+        0xC0, 0xC1, 0xC2, 0xC3, 0xC4, 0xC5,
+        0xC6, 0xC7, 0xC8, 0xC9, 0xCA, 0xCB, 0xCC, 0xCD, 0xCE, 0xCF, 0xD0, 0xD1, 0xD2, 0xD3, 0xD4,
+        0xD5, 0xD6, 0xD7
     })
         {
             CAPTURE(b);