Update module go.opentelemetry.io/otel/sdk/log to v0.21.0 [SECURITY]

[renovate]

This PR contains the following updates:

Package	Change	Age	Confidence
go.opentelemetry.io/otel/sdk/log	v0.20.0 → v0.21.0

---

OpenTelemetry-Go: BatchProcessor can busy-spin when export buffer is full

CVE-2026-81872 / GHSA-hjf4-fphr-2h65

More information

Details

Summary

A BatchingProcessor in go.opentelemetry.io/otel/sdk/log can enter a tight CPU loop when the asynchronous export buffer is full. Under exporter backpressure, attacker-driven high-volume log emission can keep the queue at or above the batch size, causing repeated immediate export retries and a denial of service through CPU exhaustion.

Introduced in commit: 4af9c20

Details

NewBatchingProcessor wraps the exporter with newBufferExporter(exporter, 1) (sdk/log/batch.go:116-122), so the asynchronous export input can fill quickly when the downstream exporter blocks. The poll goroutine dequeues a batch with b.q.TryDequeue, calls b.exporter.EnqueueExport(r), and then immediately sends on b.pollTrigger whenever qLen >= b.batchSize (sdk/log/batch.go:129-165).

bufferExporter.EnqueueExport is non-blocking: it sends to e.input if possible and returns false in the default case when the channel is full (sdk/log/exporter.go:221-248). TryDequeue leaves q.len unchanged when the write callback returns false (sdk/log/batch.go:289-314). Therefore, while the exporter is backpressured, EnqueueExport fails, the queue remains at or above one full batch, and the poll loop continuously retriggers itself without waiting for the ticker.

PoC

validation-artifact.zip

The validation artifact contains a PoC bundle:

• validation-artifact.tar:main.go: PoC source.
• validation-artifact.tar:README.md: build/run notes.
• validation-artifact.tar:build_failed.log: captured build failure from the validation environment.

The PoC configures a blocking exporter and a BatchingProcessor with WithExportMaxBatchSize(1), WithExportInterval(5*time.Second), and WithMaxQueueSize(2048). It emits 1000 records, records a CPU profile for 750 ms while the exporter is blocked, then writes /workspace/validation_artifacts/busyloop.pprof.

Reproduction steps from an affected checkout at commit 4af9c20:

cd /workspace/opentelemetry-go
git checkout 4af9c20

mkdir -p validation_poc/busyloop /workspace/validation_artifacts /tmp/batchingprocessor-busyloop-poc
tar -xf /path/to/this/finding/validation-artifact.tar -C /tmp/batchingprocessor-busyloop-poc
cp /tmp/batchingprocessor-busyloop-poc/main.go validation_poc/busyloop/main.go

go build -o validation_poc/busyloop/busyloop ./validation_poc/busyloop
./validation_poc/busyloop/busyloop
go tool pprof -top /workspace/validation_artifacts/busyloop.pprof

Expected program output:

cpu profile written to /workspace/validation_artifacts/busyloop.pprof

Expected profile evidence: hot functions should include (*BatchingProcessor).poll, (*queue).TryDequeue, and (*bufferExporter).EnqueueExport, showing repeated export attempts while the exporter is blocked.

Impact

This is an availability vulnerability: uncontrolled CPU consumption caused by a busy-spin retry loop. Applications using sdk/log BatchingProcessor are impacted when an attacker can cause sustained log emission and the configured exporter or downstream collector is slow, blocked, or otherwise backpressured. The impact is limited to the embedding process but can degrade or deny service for that application.

Severity

• CVSS Score: 6.3 / 10 (Medium)
• Vector String: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

References

• https://github.com/open-telemetry/opentelemetry-go/security/advisories/GHSA-hjf4-fphr-2h65
• https://nvd.nist.gov/vuln/detail/CVE-2026-81872
• https://github.com/open-telemetry/opentelemetry-go/issues/6797
• https://github.com/open-telemetry/opentelemetry-go/pull/8620
• https://github.com/open-telemetry/opentelemetry-go/commit/ba71b09e6ed272e93a669aeaec1e98b1df4cc582
• https://github.com/open-telemetry/opentelemetry-go/releases/tag/sdk/log/v0.21.0
• https://github.com/advisories/GHSA-hjf4-fphr-2h65

This data is provided by the GitHub Advisory Database (CC-BY 4.0).

---

Configuration

📅 Schedule: (UTC)

• Branch creation
  • At any time (no schedule defined)
• Automerge
  • At any time (no schedule defined)

🚦 Automerge: Disabled by config. Please merge this manually once you are satisfied.

♻ Rebasing: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

🔕 Ignore: Close this PR and you won't be reminded about this update again.

---

• If you want to rebase/retry this PR, check this box

---

This PR was generated by Mend Renovate. View the repository job log.

[renovate]

ℹ️ Artifact update notice

File name: go.mod

In order to perform the update(s) described in the table above, Renovate ran the go get command, which resulted in the following additional change(s):

• 7 additional dependencies were updated

Details:

Package	Change
go.opentelemetry.io/otel	v1.44.0 -> v1.45.0
go.opentelemetry.io/otel/log	v0.20.0 -> v0.21.0
go.opentelemetry.io/otel/sdk	v1.44.0 -> v1.45.0
go.opentelemetry.io/otel/trace	v1.44.0 -> v1.45.0
github.com/go-logr/logr	v1.4.3 -> v1.4.4
go.opentelemetry.io/otel/metric	v1.44.0 -> v1.45.0
golang.org/x/sys	v0.45.0 -> v0.47.0