{"id":"CVE-2026-42191","aliases":["GHSA-4625-4j76-fww9"],"url":"https://o3.security/vulnerability/CVE-2026-42191","summary":"OpenTelemetry.Exporter.OpenTelemetryProtocol: Disk retry default temp path enables local blob injection for OTLP Exporter","details":"### Summary\n\nThe OTLP disk retry feature in `OpenTelemetry.Exporter.OpenTelemetryProtocol` silently fell back to `Path.GetTempPath()` when `OTEL_DOTNET_EXPERIMENTAL_OTLP_RETRY=disk` was set but `OTEL_DOTNET_EXPERIMENTAL_OTLP_DISK_RETRY_DIRECTORY_PATH` was not configured.\n\nThe exporter stored and loaded `*.blob` files under fixed, signal-named subdirectories (`traces`, `metrics`, `logs`) beneath that shared temporary root path.\n\nOn multi-user systems where the temporary directory is accessible to other local accounts, this exposed three attack surfaces:\n\n- **Blob injection (integrity):** an attacker could write crafted `*.blob` files into the predictable path; the exporter picks them up on the next retry cycle and forwards them to the configured OTLP endpoint under the application's identity.\n- **Telemetry disclosure (confidentiality):** an attacker reads `*.blob` files written by the application between export failures, recovering encoded telemetry payloads (spans, metric data points, log records).\n- **Resource exhaustion (availability):** an attacker deposits numerous or oversized blob files, degrading retry-loop performance or consuming disk space.\n\n### Details\n\n#### Preconditions\n\n1. `OTEL_DOTNET_EXPERIMENTAL_OTLP_RETRY` is set to `disk`.\n2. `OTEL_DOTNET_EXPERIMENTAL_OTLP_DISK_RETRY_DIRECTORY_PATH` is not set, causing the exporter to resolve the blob storage root using the `System.IO.Path.GetTempPath()` API.\n3. A local attacker has read or write access to the process' temporary directory (e.g., `/tmp` on Linux, or `%TEMP%` on a multi-user Windows installation).\n\n#### Exploit path\n\n1. A target application starts with `OTEL_DOTNET_EXPERIMENTAL_OTLP_RETRY=disk` and no explicit blob directory. The exporter resolves the storage root to `Path.GetTempPath()`, producing paths such as `%TEMP%\\traces`, `%TEMP%\\metrics`, and `%TEMP%\\logs` (or `/tmp/traces` etc. on Linux).\n2. **Injection scenario:** before or during the application's retry window, an attacker writes crafted `*.blob` files into one of those signal subdirectories. On the next retry interval (by default every 60 seconds), [`OtlpExporterPersistentStorageTransmissionHandler`](https://github.com/open-telemetry/opentelemetry-dotnet/blob/c724f4bd6fd88e9a599af1668bf7af9487155b62/src/OpenTelemetry.Exporter.OpenTelemetryProtocol/Implementation/Transmission/OtlpExporterPersistentStorageTransmissionHandler.cs) scans the directory, loads the attacker-supplied blobs, and forwards them to the configured OTLP endpoint using the application's identity and transport credentials.\n3. **Disclosure scenario:** the attacker reads `*.blob` files that the application wrote after a transient export failure, recovering the full serialized telemetry payloads (spans, metric data points, or log records in Protobuf encoding).\n5. **DoS scenario:** the attacker deposits a large number of oversized blob files in the temporary subdirectories, causing the retry loop to consume excess CPU/IO processing them, potentially exhausting available disk space.\n\n### Mitigations\n\nIf an immediate upgrade to a patched version is not possible:\n\n1. Avoid enabling disk retry in shared environments.\n2. Configure a dedicated directory with strict ACL/ownership and least privilege.\n3. Ensure the directory is not shared across tenants/users.\n4. Monitor for unexpected `*.blob` files or abnormal retry backlog growth.\n\n### Resources\n\n- [#7106](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7106)","published":"2026-05-12T19:12:03.221Z","modified":"2026-08-12T03:51:39.169791591Z","cvss":{"score":6.5,"severity":"MEDIUM","vector":"CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:L"},"epss":{"score":0.00108,"percentile":0.01394,"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/7106","label":"open-telemetry/opentelemetry-dotnet#7106"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/42xxx/CVE-2026-42191.json"},{"type":"ADVISORY","url":"https://github.com/open-telemetry/opentelemetry-dotnet/security/advisories/GHSA-4625-4j76-fww9"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-42191"},{"type":"FIX","url":"https://github.com/open-telemetry/opentelemetry-dotnet/pull/7106"},{"type":"WEB","url":"https://github.com/open-telemetry/opentelemetry-dotnet/commit/78dffdc5ebdf3dc090fdb94e3f1a32d3d1e26dfd"},{"type":"PACKAGE","url":"https://github.com/open-telemetry/opentelemetry-dotnet"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:39.169791591Z"}}