CVE-2026-40891: OpenTelemetry dotnet: Unbounded `grpc-status-details-bin` parsing in OTLP/gRPC retry handling
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.
Other sources
OpenTelemetry dotnet is a dotnet telemetry framework. From 1.13.1 to before 1.15.2, 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). This vulnerability is fixed in 1.15.2.
— MITRE
Affected Software
Remediation
Event History
Frequently Asked Questions
What is the severity of CVE-2026-40891?
The severity of CVE-2026-40891 is classified as medium due to potential Denial of Service vulnerabilities.
How do I fix CVE-2026-40891?
To fix CVE-2026-40891, upgrade OpenTelemetry dotnet to version 1.15.2 or later.
What versions are affected by CVE-2026-40891?
CVE-2026-40891 affects OpenTelemetry dotnet versions from 1.13.1 to before 1.15.2.
What impact does CVE-2026-40891 have on my application?
CVE-2026-40891 can result in unbounded parsing of grpc-status-details-bin, potentially leading to application crashes.
Is CVE-2026-40891 a high-risk vulnerability?
CVE-2026-40891 is considered a medium-risk vulnerability primarily due to its impact on application stability.