# CVE-2026-42191: OpenTelemetry .NET OTLP Exporter insecure temporary file permissions

Source: https://junglewise.ai/threats/cve-2026-42191-opentelemetry-net-otlp-exporter-insecure-temporary-file  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-12. Updated: 2026-05-26  
License: CC BY 4.0 with a link back

CVE-2026-42191 · Severity: medium · CVSS 6.5 · Published 2026-05-12

A vulnerability in the OpenTelemetry .NET exporter library could allow a local attacker on a shared system to intercept or manipulate monitoring data. The library, which is used to send application performance and health data to monitoring services, incorrectly used a shared temporary folder to store data during network failures. This could lead to the exposure of sensitive application logs and metrics, the injection of fake monitoring data, or a denial-of-service by filling up disk space.

Technologies: [OpenTelemetry.Exporter.OpenTelemetryProtocol (NuGet)](https://junglewise.ai/threats/technologies/opentelemetry-exporter-opentelemetryprotocol). Vendors: [NuGet](https://junglewise.ai/threats/vendors/nuget), [Opentelemetry](https://junglewise.ai/threats/vendors/opentelemetry).

## Quick answers

**Is CVE-2026-42191 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-42191 being exploited in the wild.

**How severe is CVE-2026-42191?** Medium severity, with a CVSS score of 6.5, published 12 May 2026.

**Which products and versions are affected?** OpenTelemetry.Exporter.OpenTelemetryProtocol (NuGet) >= 1.8.0, <= 1.15.2, ECOSYSTEM:introduced=1.8.0,fixed=1.15.3; Opentelemetry Exporter.OpenTelemetryProtocol 1.8.0 to 1.15.2.

**Is there a fix for CVE-2026-42191?** Yes. OpenTelemetry.Exporter.OpenTelemetryProtocol (NuGet): upgrade to 1.15.3 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-42191 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2026-42191?** Check whether you run OpenTelemetry.Exporter.OpenTelemetryProtocol (NuGet) or Opentelemetry Exporter.OpenTelemetryProtocol at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- OpenTelemetry.Exporter.OpenTelemetryProtocol (NuGet): upgrade to 1.15.3 or later

  ```sh
  dotnet add package OpenTelemetry.Exporter.OpenTelemetryProtocol --version 1.15.3
  ```


## Technical details

The vulnerability exists in the OTLP disk retry feature of OpenTelemetry.Exporter.OpenTelemetryProtocol (versions 1.8.0 to 1.15.2). When the 'disk' retry mode is enabled without a specific directory path configured, the exporter defaults to using the system's shared temporary directory (Path.GetTempPath()). Because the subdirectories used (traces, metrics, logs) are predictable and often lack restrictive permissions on multi-user systems, a local attacker can perform 'blob injection' by placing malicious telemetry files into these folders, which the application will then sign and forward. Additionally, attackers can read existing telemetry blobs to steal sensitive data or perform resource exhaustion by flooding the directory with large files. The issue is resolved in version 1.15.3 by requiring an explicit, secure directory path when disk retry is enabled.

## Affected products

- OpenTelemetry OpenTelemetry.Exporter.OpenTelemetryProtocol 1.8.0 to 1.15.2

## Identifiers

- CVE-2026-42191
- GHSA-4625-4j76-fww9

## Timeline

- 2026-04-17: patched: Pull request merged to fix insecure default path
- 2026-04-27: advisory: Vendor security advisory published via GitHub
- 2026-05-12: disclosed: CVE-2026-42191 published to NVD

## References

- [https://github.com/open-telemetry/opentelemetry-dotnet/pull/7106](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7106)
- [https://github.com/open-telemetry/opentelemetry-dotnet/security/advisories/GHSA-4625-4j76-fww9](https://github.com/open-telemetry/opentelemetry-dotnet/security/advisories/GHSA-4625-4j76-fww9)

## Related threats

- [OpenTelemetry dotnet: Unbounded `grpc-status-details-bin` parsing in OTLP/gRPC retry handling](https://junglewise.ai/threats/cve-2026-40891-opentelemetry-dotnet-unbounded-grpc-status-details-bin-parsing-in)
- [OpenTelemetry dotnet: OTLP exporter reads unbounded HTTP response bodies](https://junglewise.ai/threats/cve-2026-40182-opentelemetry-dotnet-otlp-exporter-reads-unbounded-http-response)