CVE-2026-40891: OpenTelemetry dotnet Unbounded `grpc-status-details-bin` Parsing Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-mr8r-92fq-pj8p",
  "modified" : "2026-04-23T21:40:29Z",
  "published" : "2026-04-23T21:40:29Z",
  "aliases" : [ "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.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "NuGet",
      "name" : "OpenTelemetry.Exporter.OpenTelemetryProtocol"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "1.13.1"
      }, {
        "fixed" : "1.15.3"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "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" : "WEB",
    "url" : "https://github.com/open-telemetry/opentelemetry-dotnet/pull/5980"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/open-telemetry/opentelemetry-dotnet/pull/7064"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/open-telemetry/opentelemetry-dotnet"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-789" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-23T21:40:29Z",
    "nvd_published_at" : "2026-04-23T18:16:28Z"
  }
}