CVE-2026-29181

OpenTelemetry-Go: Multi-value baggage header extraction causes excessive allocations in go.opentelemetry.io/otel

multi-value `baggage:` header extraction parses each header field-value independently and aggregates members across values. this allows an attacker to amplify cpu and allocations by sending many `baggage:` header lines, even when each individual value is within the 8192-byte per-value parse limit. ## severity HIGH (availability / remote request amplification) ## relevant links - repository: https://github.com/open-telemetry/opentelemetry-go - pinned callsite: https://github.com/open-telemetry/opentelemetry-go/blob/1ee4a4126dbdd1bc79e9fae072fa488beffac52a/propagation/baggage.go#L58 ## vulnerability details **pins:** open-telemetry/opentelemetry-go@1ee4a4126dbdd1bc79e9fae072fa488beffac52a **as-of:** 2026-02-04 **policy:** direct (no program scope provided) **callsite:** propagation/baggage.go:58 (`extractMultiBaggage`) **attacker control:** inbound HTTP request headers (many `baggage` field-values) → `propagation.HeaderCarrier.Values("baggage")` → repeated `baggage.Parse` + member aggregation ### root cause `extractMultiBaggage` iterates over all `baggage` header field-values and parses each one independently, then appends members into a shared slice. the 8192-byte parsing cap applies per header value, but the multi-value path repeats that work once per header line (bounded only by the server/proxy header byte limit). ### impact in a default `net/http` configuration (max header bytes 1mb), a single request with many `baggage:` header field-values can cause large per-request allocations and increased latency. example from the attached PoC harness (darwin/arm64; 80 values; 40 requests): - canonical: `per_req_alloc_bytes=10315458` and `p95_ms=7` - control: `per_req_alloc_bytes=133429` and `p95_ms=0` ## proof of concept canonical: ```bash mkdir -p poc unzip poc.zip -d poc cd poc make test ``` output (excerpt): ``` [CALLSITE_HIT]: propagation/baggage.go:58 extractMultiBaggage [PROOF_MARKER]: baggage_multi_value_amplification p95_ms=7 per_req_alloc_bytes=10315458 per_req_allocs=16165 ``` control: ```bash cd poc make control ``` control output (excerpt): ``` [NC_MARKER]: baggage_single_value_baseline p95_ms=0 per_req_alloc_bytes=133429 per_req_allocs=480 ``` **expected:** multiple `baggage` header field-values should be semantically equivalent to a single comma-joined `baggage` value and should not multiply parsing/alloc work within the effective header byte budget. **actual:** multiple `baggage` header field-values trigger repeated parsing and member aggregation, causing high per-request allocations and increased latency even when each individual value is within 8192 bytes. ## fix recommendation avoid repeated parsing across multi-values by enforcing a global budget and/or normalizing multi-values into a single value before parsing. one mitigation approach is to treat multi-values as a single comma-joined string and cap total parsed bytes (for example 8192 bytes total). **fix accepted when:** under the default PoC harness settings, canonical stays within 2x of control for `per_req_alloc_bytes` and `per_req_allocs`, and `p95_ms` stays below 2ms. [poc.zip](https://github.com/user-attachments/files/25079945/poc.zip) [PR_DESCRIPTION.md](https://github.com/user-attachments/files/25079946/PR_DESCRIPTION.md)

OpenTelemetry-Go es la implementación en Go de OpenTelemetry. Desde la versión 1.36.0 hasta la 1.40.0, la extracción de encabezados 'baggage' con múltiples valores analiza cada par campo-valor del encabezado de forma independiente y agrega los miembros a través de los valores. Esto permite a un atacante amplificar el uso de CPU y las asignaciones de memoria enviando muchas líneas de encabezado 'baggage', incluso cuando cada valor individual está dentro del límite de análisis de 8192 bytes por valor. Esta vulnerabilidad está corregida en la versión 1.41.0.