CVE-2026-39882

overview: this report shows that the otlp HTTP exporters (traces/metrics/logs) read the full HTTP response body into an in-memory bytes.Buffer without a size cap.

this is exploitable for memory exhaustion when the configured collector endpoint is attacker-controlled (or a network attacker can mitm the exporter connection).

severity

HIGH

not claiming: this is a remote dos against every default deployment. claiming: if the exporter sends traces to an untrusted collector endpoint (or over a network segment where mitm is realistic), that endpoint can crash the process via a large response body.

callsite (pinned):

• exporters/otlp/otlptrace/otlptracehttp/client.go:199
• exporters/otlp/otlptrace/otlptracehttp/client.go:230
• exporters/otlp/otlpmetric/otlpmetrichttp/client.go:170
• exporters/otlp/otlpmetric/otlpmetrichttp/client.go:201
• exporters/otlp/otlplog/otlploghttp/client.go:190
• exporters/otlp/otlplog/otlploghttp/client.go:221

permalinks (pinned):

• https://github.com/open-telemetry/opentelemetry-go/blob/248da958375e4dfb4a1105645107be3ef04b1c59/exporters/otlp/otlptrace/otlptracehttp/client.go#L199
• https://github.com/open-telemetry/opentelemetry-go/blob/248da958375e4dfb4a1105645107be3ef04b1c59/exporters/otlp/otlptrace/otlptracehttp/client.go#L230
• https://github.com/open-telemetry/opentelemetry-go/blob/248da958375e4dfb4a1105645107be3ef04b1c59/exporters/otlp/otlpmetric/otlpmetrichttp/client.go#L170
• https://github.com/open-telemetry/opentelemetry-go/blob/248da958375e4dfb4a1105645107be3ef04b1c59/exporters/otlp/otlpmetric/otlpmetrichttp/client.go#L201
• https://github.com/open-telemetry/opentelemetry-go/blob/248da958375e4dfb4a1105645107be3ef04b1c59/exporters/otlp/otlplog/otlploghttp/client.go#L190
• https://github.com/open-telemetry/opentelemetry-go/blob/248da958375e4dfb4a1105645107be3ef04b1c59/exporters/otlp/otlplog/otlploghttp/client.go#L221

root cause: each exporter client reads resp.Body using io.Copy(&respData, resp.Body) into a bytes.Buffer on both success and error paths, with no upper bound.

impact: a malicious collector can force large transient heap allocations during export (peak memory scales with attacker-chosen response size) and can potentially crash the instrumented process (oom).

affected component:

• go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp
• go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp
• go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp

repro (local-only):

unzip poc.zip -d poc
cd poc
make canonical resp_bytes=33554432 chunk_delay_ms=0

expected output contains:

[CALLSITE_HIT]: otlptracehttp.UploadTraces::io.Copy(resp.Body)
[PROOF_MARKER]: resp_bytes=33554432 peak_alloc_bytes=118050512

control (same env, patched target):

unzip poc.zip -d poc
cd poc
make control resp_bytes=33554432 chunk_delay_ms=0

expected control output contains:

[CALLSITE_HIT]: otlptracehttp.UploadTraces::io.Copy(resp.Body)
[NC_MARKER]: resp_bytes=33554432 peak_alloc_bytes=512232

attachments: poc.zip (attached)

PR_DESCRIPTION.md

attack_scenario.md

poc.zip

Fixed in: https://github.com/open-telemetry/opentelemetry-go/pull/8108