OpenTelemetry Core: Unbounded memory allocation in W3C Baggage propagation

Overview

W3CBaggagePropagator.extract() in @opentelemetry/core does not enforce size limits when parsing inbound baggage HTTP headers. The W3C Baggage specification recommends a maximum of 8,192 bytes and 180 entries; these limits were only enforced on the outbound (inject()) path, not on the inbound (extract()) path. Parsing oversized baggage causes memory allocation proportional to the header size without any cap.

Impact

The practical availability impact for most Node.js deployments is limited. Node.js enforces a default --max-http-header-size of 16,384 bytes on the total combined size of all HTTP headers, constraining what an external attacker can deliver before the propagator is reached. Additionally, the header is already in memory (parsed by the HTTP layer) by the time it reaches the propagator - the additional allocation is the overhead of splitting into entry objects, not an unbounded read.

The risk is higher when transport-layer limits are absent - e.g., non-HTTP transports (messaging systems, custom TextMapGetter implementations) or deployments that have raised --max-http-header-size.

Remediation

Update @opentelemetry/core to version 2.8.0 or later. The fix enforces limits consistent with the W3C Baggage specification at the propagator level:

• Maximum total baggage size: 8,192 bytes
• Maximum number of entries: 180
• Maximum per-entry size: 4,096 bytes

Headers that exceed these limits are truncated at the point the limit is reached.

Workarounds

Ensure header size limits are configured at the server or gateway level. The default Node.js HTTP header limit (16 KB) mitigates external attack vectors independently of this fix. For non-HTTP transports receiving baggage from untrusted sources, validate input size before passing it to the propagator.

References

• W3C Baggage Specification - Limits
• opentelemetry-java: GHSA-rcgg-9c38-7xpx
• opentelemetry-go: GHSA-mh2q-q3fh-2475

Credit

Reported by tonghuaroot.