{"id":"CVE-2026-40891","aliases":["GHSA-mr8r-92fq-pj8p"],"url":"https://o3.security/vulnerability/CVE-2026-40891","summary":"OpenTelemetry dotnet: Unbounded `grpc-status-details-bin` parsing in OTLP/gRPC retry handling","details":"### Summary\n\nWhen 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).\n\n### Details\n\n#5980 introduced a retry path that parses `grpc-status-details-bin` to extract gRPC retry delay information for retryable responses.\n\nOn that path:\n\n- `OtlpGrpcExportClient` captures `grpc-status-details-bin` from retryable status responses (`ResourceExhausted` / `Unavailable`).\n- `OtlpRetry` invokes `GrpcStatusDeserializer.TryGetGrpcRetryDelay` using this untrusted trailer value.\n- `GrpcStatusDeserializer.DecodeBytes` decoded a protobuf varint length and allocated `new byte[length]` without validating the bounds against the remaining payload size.\n\nA 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.\n\n### Impact\n\nIf 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).\n\n### Mitigation\n\nThe 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.\n\n### Workarounds\n\nNone known.\n\n### Remediation\n\n[#7064](https://github.com/open-telemetry/opentelemetry-dotnet/pull/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.\n\nThis causes malformed or truncated `grpc-status-details-bin` payloads to fail safely instead of attempting unbounded allocation.","published":"2026-04-23T17:54:36.033Z","modified":"2026-08-12T03:51:17.386143840Z","cvss":{"score":5.3,"severity":"MEDIUM","vector":"CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H"},"epss":{"score":0.00192,"percentile":0.09164,"asOf":"2026-08-14"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"NuGet","name":"OpenTelemetry.Exporter.OpenTelemetryProtocol","fixedVersion":"1.15.3"}],"fix":{"url":"https://github.com/open-telemetry/opentelemetry-dotnet/pull/5980","label":"open-telemetry/opentelemetry-dotnet#5980"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/40xxx/CVE-2026-40891.json"},{"type":"ADVISORY","url":"https://github.com/open-telemetry/opentelemetry-dotnet/security/advisories/GHSA-mr8r-92fq-pj8p"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-40891"},{"type":"FIX","url":"https://github.com/open-telemetry/opentelemetry-dotnet/pull/5980"},{"type":"FIX","url":"https://github.com/open-telemetry/opentelemetry-dotnet/pull/7064"},{"type":"PACKAGE","url":"https://github.com/open-telemetry/opentelemetry-dotnet"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:17.386143840Z"}}