GHSA-9hj4-r449-hfvc

Описание

Summary

Ruby's JSON native C extension clears the consumed JSON::ResumableParser input buffer but leaves state.start, state.cursor, and state.end pointing into released storage.

When partial_value reconstructs an incomplete object containing duplicate keys, the duplicate-key warning path calls cursor_position, which dereferences those stale pointers. This results in a heap-use-after-free and can terminate the Ruby process.

An attacker who can supply JSON stream data to an application using JSON::ResumableParser may cause process termination when the application calls partial_value on incomplete attacker-controlled input containing duplicate object keys.

The issue was reproduced in the native C extension from the official RubyGems releases:

• JSON 2.20.0
• JSON 2.21.0
• JSON 2.21.1

The attached evidence demonstrates:

• an AddressSanitizer-confirmed heap-use-after-free;
• a native SIGSEGV using the official JSON 2.21.1 RubyGem;
• an end-to-end loopback TCP attacker/victim reproduction;
• four differential controls;
• successful execution after applying a tested patch control.

This was originally reported privately through Ruby's HackerOne program as report #3867755. A Ruby maintainer independently confirmed reproduction of the ASan failure and requested that further coordination continue through this private advisory.

No code execution or information disclosure is claimed.

Details

The affected source is:

The vulnerable sequence in JSON 2.21.1 is:

1. cResumableParser_parse reaches the end of the current input buffer.
2. It calls json_str_clear(parser->buffer).
3. It sets parser->buffer = Qfalse.
4. The parser-state pointers into the released buffer are not reset.
5. partial_value makes a shallow copy of the parser state.
6. Reconstructing an incomplete object containing duplicate keys reaches the duplicate-key warning path.
7. cursor_position walks through the stale input pointers and reads released memory.

Relevant source locations:

• Buffer release: https://github.com/ruby/json/blob/fd61def38b9bb859fee7eec8e7d3143600e5b347/ext/json/ext/parser/parser.c#L2562-L2569

• Parser-state copy: https://github.com/ruby/json/blob/fd61def38b9bb859fee7eec8e7d3143600e5b347/ext/json/ext/parser/parser.c#L2647-L2654

• Stale-pointer read in cursor_position: https://github.com/ruby/json/blob/fd61def38b9bb859fee7eec8e7d3143600e5b347/ext/json/ext/parser/parser.c#L590-L628

• Duplicate-key handling path: https://github.com/ruby/json/blob/fd61def38b9bb859fee7eec8e7d3143600e5b347/ext/json/ext/parser/parser.c#L1196-L1255

When input is supplied to the resumable parser, the parser state stores direct pointers into the backing Ruby string:

After the current buffer has been consumed, cResumableParser_parse clears the string and removes the parser's reference to it:

This path does not invalidate or replace:

JSON::ResumableParser#partial_value subsequently makes a shallow copy of the parser structure:

When the partial object contains duplicate keys, reconstruction follows this call path:

cursor_position then reads through pointers that may refer to released storage.

AddressSanitizer reports:

The reproducer follows the normal resumable-parser API sequence:

The issue does not require:

• an application-defined callback;
• explicit garbage collection;
• parser reentrancy;
• custom parser options;
• an attacker-supplied Ruby object;
• manual modification of native parser state.

The release-build crash reproduced on JSON 2.20.0, 2.21.0, and 2.21.1.

This report covers the native C-extension implementation. The separate Java-platform implementation was not tested and is not claimed to be affected.

PoC

The complete evidence bundle is attached as:

SHA-256:

Requirements

• Linux
• Ruby with development headers
• C compiler
• make
• RubyGems

Release-build, network, and differential reproduction

Extract the attachment:

Run the official JSON 2.21.1 release-build proof, loopback network proof, and differential controls:

Expected primary results:

The following four differential controls must also report result=PASS:

The release-build crash stack includes:

AddressSanitizer reproduction

Run:

Expected vulnerable result:

Expected patched-control result:

Affected-version matrix

The release-build crash was reproduced three times for each of the following official RubyGems releases:

Additional evidence is included in:

Impact

This is a use-after-free that can result in native Ruby process termination.

An attacker must be able to supply JSON stream data to an application that:

1. uses JSON::ResumableParser;
2. processes attacker-controlled streaming input;
3. calls partial_value after parsing an incomplete document containing duplicate object keys.

In network-facing deployments meeting these conditions, an attacker can cause process termination and denial of service.

The release-build crash was reproduced consistently in the tested Linux environment. The AddressSanitizer result confirms the underlying heap-use-after-free independently of normal allocator behavior.

The demonstrated impact is:

No confidentiality impact, integrity impact, arbitrary code execution, or information disclosure is claimed.

Suggested remediation

Before clearing or releasing the resumable parser's input buffer, invalidate or replace every parser-state pointer that refers to the buffer's backing storage.

Delayed code paths such as duplicate-key warning generation must not calculate cursor positions using pointers after the corresponding buffer has been released.

The attached patch-control.diff demonstrates one tested control and is provided for validation rather than as a required final implementation.