Details

Summary

When exporting telemetry to a back-end/collector over gRPC or HTTP using OpenTelemetry Protocol format (OTLP), if the request results in a unsuccessful request (i.e. HTTP 4xx or 5xx), the response is read into memory with no upper-bound on the number of bytes consumed.

This could cause memory exhaustion in the consuming application if the configured back-end/collector endpoint is attacker-controlled (or a network attacker can MitM the connection) and an extremely large body is returned by the response.

Details

https://github.com/open-telemetry/opentelemetry-dotnet/pull/6564 introduced a change to read the response body when a non-200 HTTP status code is received when exporting telemetry to aid debugging by operators so that the error response is included in the logs emitted by the exporter for both gRPC and HTTP/protobuf.

An unintended consequence of this change is that the response body is fully read into memory when received with no upper-bound.

This vulnerability was surfaced during the investigation of GHSA-w8rr-5gcm-pp58.

Impact

If an application using the OTLP exporter is configured to use a back-end/collector endpoint that is attacker-controlled (or a network attacker can MitM the connection) and an extremely large body is returned by the response the application could have its memory exhausted and create a denial-of-service condition.

Mitigation

The application's configured back-end/collector endpoint needs to behave maliciously. If the collector/back-end is a well-behaved implementation response bodies should not be excessively large if a request error occurs.

Workarounds

None known.

Remediation

#​7017 updates the OTLP exporter for both gRPC and HTTP to:

• Limit the number of bytes read from the response body in an error condition to 4MiB (see https://github.com/open-telemetry/opentelemetry-proto/pull/781);
• Only attempt to read the response body if OpenTelemetry error logging is enabled.

Severity

• CVSS Score: 5.3 / 10 (Medium)
• Vector String: CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

References

• https://github.com/open-telemetry/opentelemetry-dotnet/security/advisories/GHSA-q834-8qmm-v933
• https://nvd.nist.gov/vuln/detail/CVE-2026-40182
• https://github.com/open-telemetry/opentelemetry-dotnet/pull/6564
• https://github.com/open-telemetry/opentelemetry-dotnet/pull/7017
• https://github.com/open-telemetry/opentelemetry-proto/pull/781
• https://github.com/advisories/GHSA-q834-8qmm-v933

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

Details

Summary

When exporting telemetry over gRPC using the OpenTelemetry Protocol (OTLP), the exporter may parse a server-provided grpc-status-details-bin trailer during retry handling. Prior to the fix, a malformed trailer could encode an extremely large length-delimited protobuf field which was used directly for allocation, allowing excessive memory allocation and potential denial of service (DoS).

Details

#​5980 introduced a retry path that parses grpc-status-details-bin to extract gRPC retry delay information for retryable responses.

On that path:

• OtlpGrpcExportClient captures grpc-status-details-bin from retryable status responses (ResourceExhausted / Unavailable).
• OtlpRetry invokes GrpcStatusDeserializer.TryGetGrpcRetryDelay using this untrusted trailer value.
• GrpcStatusDeserializer.DecodeBytes decoded a protobuf varint length and allocated new byte[length] without validating the bounds against the remaining payload size.

A malicious or compromised collector (or a MitM in weakly-protected deployments) could return a crafted grpc-status-details-bin payload that forces oversized allocation and memory exhaustion in the instrumented process.

Impact

If an OTLP/gRPC endpoint is attacker-controlled (or traffic is intercepted), a crafted retryable response can trigger large allocations during trailer parsing, which may exhaust memory and cause process instability/crash (availability impact / DoS).

Mitigation

The application's configured back-end/collector endpoint needs to behave maliciously. If the collector/back-end is a well-behaved implementation response bodies should not be excessively large if a request error occurs.

Workarounds

None known.

Remediation

#​7064 updates GrpcStatusDeserializer to validate decoded length-delimited field sizes before allocation by ensuring the requested length is sane and does not exceed the remaining payload.

This causes malformed or truncated grpc-status-details-bin payloads to fail safely instead of attempting unbounded allocation.

Severity

• CVSS Score: 5.3 / 10 (Medium)
• Vector String: CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

References

• https://github.com/open-telemetry/opentelemetry-dotnet/security/advisories/GHSA-mr8r-92fq-pj8p
• https://nvd.nist.gov/vuln/detail/CVE-2026-40891
• https://github.com/open-telemetry/opentelemetry-dotnet/pull/5980
• https://github.com/open-telemetry/opentelemetry-dotnet/pull/7064
• https://github.com/advisories/GHSA-mr8r-92fq-pj8p

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

v1.15.3

Release details: 1.15.3

• Breaking change: Fixed tracestate parsing to reject keys that do not
  begin with a lowercase letter, including keys beginning with digits, to
  align with the W3C Trace Context specification.
• Breaking change: Fixed an insecure disk retry default for OTLP export.
  Disk retry now requires OTEL_DOTNET_EXPERIMENTAL_OTLP_DISK_RETRY_DIRECTORY_PATH
  when OTEL_DOTNET_EXPERIMENTAL_OTLP_RETRY=disk is configured.
• Improve efficiency of parsing of baggage and B3 propagation headers.
• OtlpLogExporter now uses IHttpClientFactory on .NET 8+.
• Fixed an issue in OTLP/gRPC retry handling where parsing gRPC status.
• Fixed OTEL_SPAN_ATTRIBUTE_VALUE_LENGTH_LIMIT not being applied.
• Fixed baggage and trace headers not respecting the maximum length in some cases.
• Fixed BaggagePropagator to trim optional whitespace (OWS) around =
  separators when parsing the baggage header.
• Fixed BaggagePropagator to strip baggage properties from values when
  parsing the baggage header.
• Fixed OTLP persistent storage clean-up handling for malformed filenames.
• Fixed resource leak in batch and periodic exporting task workers for Blazor/WASM.
• Fixed LogRecord.LogLevel to preserve LogLevel.None.
• Fixed OTEL_TRACES_SAMPLER_ARG handling for out-of-range values.
• Fixed an issue with OTLP disk retry storage where metrics and logs used the
  traces storage directory.
• Fixed full OTLP endpoint being logged by internal diagnostics.
• Improve efficiency of parsing of baggage, B3 and Jaeger propagation headers.
• Hardened Zipkin exporter memory usage for endpoint caching and array tag
  serialization.

v1.15.2

Release details: 1.15.2

• Limit how much of the response body is read by the OTLP exporter when
  export fails and error logging is enabled.
• Added Task-based worker support for BatchExportProcessor and
  PeriodicExportingMetricReader to enable the OpenTelemetry SDK to work
  in single-threaded WebAssembly environments such as Blazor and
  Uno Platform.

v1.15.1

Release details: 1.15.1

• Breaking change: The Baggage API now disallows empty baggage names and
  treats baggage names and values as case sensitive, aligning with the latest
  Baggage API specification.
• Various bug fixes across OpenTelemetry.Api and OpenTelemetry SDK,
  including fixes for thread-safety, sampler edge cases, metrics precision,
  and observable instrument lifecycle handling.

v1.15.0

Release details: 1.15.0

• Added support for ActivitySource.TelemetrySchemaUrl
  and Meter.TelemetrySchemaUrl properties across exporters.
• Improved performance and reduced memory consumption for metrics histograms.
• Added mTLS configuration support for the OTLP exporter (client cert/key and
  CA certificate options).
• OpenTelemetry.Exporter.Zipkin is deprecated and will stop receiving updates
  in December 2026. Zipkin already supports OTLP ingestion.
  Migrate to OpenTelemetry.Exporter.OpenTelemetryProtocol as stated
  in the Deprecating Zipkin Exporter blog post.