dd-trace-rb: Improper parsing of W3C baggage headers may lead to DoS

Impact

Datadog tracing libraries that implement W3C baggage propagation parse incoming baggage HTTP headers without enforcing item-count or byte-size limits on the extract path. The DD_TRACE_BAGGAGE_MAX_ITEMS (default 64) and DD_TRACE_BAGGAGE_MAX_BYTES (default 8192) limits were applied only to baggage injection, not extraction. A remote, unauthenticated attacker can send a request whose baggage header contains an arbitrarily large number of comma-separated key-value pairs (or a single very large value). The tracer allocates a hash-map entry for each pair on every request, causing unbounded CPU and memory consumption and enabling a remote Denial of Service against any HTTP service that has the baggage propagation style enabled.
The baggage propagation style is enabled by default in most affected tracers, so any internet-facing service that has been instrumented with an affected tracer version is exposed unless the propagation style has been explicitly narrowed.

Patches

This is resolved in version 2.32.0 and later of the dd-trace-rb library.

Workarounds

If users cannot upgrade immediately:

1. Disable baggage extraction by removing baggage from DD_TRACE_PROPAGATION_STYLE (or DD_TRACE_PROPAGATION_STYLE_EXTRACT if set independently).
2. Cap the maximum HTTP request header size at an upstream proxy or web server (for example, Apache LimitRequestFieldSize, Nginx large_client_header_buffers, Envoy max_request_headers_kb).

Resources

Related upstream advisories:
opentelemetry-go GHSA-mh2q-q3fh-2475
opentelemetry-dotnet GHSA-g94r-2vxg-569j