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🛡️ CVE-2026-40891 — opentelemetry

🟡 CVSS 5.3 — Medium ✅ No Known Exploit CWE-789 NVD
5.3
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

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](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.

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

How this vulnerability can be exploited

This issue can be reached from an adjacent network, attack complexity is high, an attacker needs no privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality none, integrity none, availability high.

CVSS metrics in full

The score comes from this vector: CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

  • Attack vector: Adjacent network — the attacker has to sit on the same local or logical network.
  • Attack complexity: High — the attacker first has to win a race, learn a secret or otherwise prepare the target.
  • Privileges required: None — an unauthenticated stranger can try it.
  • User interaction: None — nobody has to be tricked into anything.
  • Scope: Unchanged — the damage stays inside the vulnerable component.
  • Confidentiality impact: None.
  • Integrity impact: None.
  • Availability impact: High — total loss, or loss the attacker controls.

Weakness class

CVE-2026-40891 is classified as CWE-789: Memory Allocation with Excessive Size Value. The product allocates memory based on an untrusted, large size value, but it does not ensure that the size is within expected limits, allowing arbitrary amounts of memory to be allocated.

Affected software

CVE-2026-40891 is recorded against 2 packages.

  • opentelemetry (from 1.13.1 up to 1.15.3)
  • opentelemetry.exporter.opentelemetryprotocol (from 1.13.1 up to 1.15.3)

Timeline and source

Published on 23 April 2026 and last revised on 17 June 2026. No public exploit is currently recorded for this entry. A vendor advisory or fix has been published. Record sourced from NVD.

References

github.com
github.com
github.com

Other advisories for this package

opentelemetry has other advisories on record. If you are patching this one, these are worth checking on the same host:

Same weakness in other software

These advisories are the same class of weakness (CWE-789: Memory Allocation with Excessive Size Value) in other software:

Details

Severity MEDIUM
CVSS Score 5.3
CVSS Vector CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
CWE CWE-789
Public Exploit ✅ No
Source NVD
Published 2026-04-23
Updated 2026-08-20
Modified 2026-06-17

Affected Packages

Software From version Fixed in
opentelemetry 1.13.1 1.15.3
opentelemetry.exporter.opentelemetryprotocol 1.13.1 1.15.3

Similar Threats

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