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Reject MessagePack/BSON binary subtypes that don't fit their wire format

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Both formats store byte_container_with_subtype's subtype (a uint64_t)
in a single byte. The writers cast to std::int8_t/std::uint8_t without
a range check, so subtypes above 255 were silently truncated modulo
256 instead of raising an error. Throw out_of_range.413 instead when
the subtype exceeds the representable range of 0-255.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
2026-09-05 17:05:58 +02:00
parent 38de588582
commit 2e83234bf4
4 changed files with 59 additions and 0 deletions
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tests/src/unit-regression2.cpp
+26
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@@ -1663,4 +1663,30 @@ TEST_CASE("regression test - excessive binary container size honors allow_except
CHECK(json::from_cbor(std::vector<std::uint8_t> {0x9b, 0, 0, 0, 0, 0, 0, 0, 0x02}, true, false).is_discarded());
}
TEST_CASE("regression test - MessagePack/BSON writers reject binary subtypes that don't fit their wire format")
{
// MessagePack: subtype 0-255 must still round-trip correctly (regression guard, pre-existing behavior)
CHECK(json::from_msgpack(json::to_msgpack(json::binary({1, 2}, 0))).get_binary().subtype() == 0);
CHECK(json::from_msgpack(json::to_msgpack(json::binary({1, 2}, 200))).get_binary().subtype() == 200);
CHECK(json::from_msgpack(json::to_msgpack(json::binary({1, 2}, 255))).get_binary().subtype() == 255);
// MessagePack: subtype > 255 must now throw instead of silently truncating
CHECK_THROWS_AS(json::to_msgpack(json::binary({1, 2}, 256)), json::out_of_range);
CHECK_THROWS_AS(json::to_msgpack(json::binary({1, 2}, 70000)), json::out_of_range);
CHECK_THROWS_WITH_AS(json::to_msgpack(json::binary({1, 2}, 70000)), "[json.exception.out_of_range.413] subtype 70000 is too large for the MessagePack ext type (max 255)", json::out_of_range);
// BSON: same pattern
json doc255 = {{"b", json::binary({1, 2}, 255)}};
CHECK(json::from_bson(json::to_bson(doc255))["b"].get_binary().subtype() == 255);
CHECK_THROWS_AS(json::to_bson(json{{"b", json::binary({1, 2}, 256)}}), json::out_of_range);
CHECK_THROWS_AS(json::to_bson(json{{"b", json::binary({1, 2}, 300)}}), json::out_of_range);
CHECK_THROWS_WITH_AS(json::to_bson(json{{"b", json::binary({1, 2}, 300)}}), "[json.exception.out_of_range.413] subtype 300 is too large for the BSON binary subtype (max 255)", json::out_of_range);
// CBOR must remain unaffected (full 64-bit subtype range already supported correctly) - regression guard
CHECK(json::from_cbor(json::to_cbor(json::binary({1, 2}, 70000)), true, true, json::cbor_tag_handler_t::store).get_binary().subtype() == 70000);
// a binary value with NO subtype at all must be completely unaffected by this change
CHECK(json::from_msgpack(json::to_msgpack(json::binary({1, 2}))).get_binary().has_subtype() == false);
}
DOCTEST_CLANG_SUPPRESS_WARNING_POP