CVE-2026-81871: open-telemetry opentelemetry-go Improper Certificate Validation

Vulnerability summary

CVE-2026-81871 is a medium (CVSS 6.3) Improper Certificate Validation vulnerability in open-telemetry opentelemetry-go. EPSS estimates a 0.20% chance of exploitation in the next 30 days, higher than 8.7% of scored vulnerabilities.

Timeline

1. 16-09-2026
   PublishedVulnerability first disclosed.
2. 17-09-2026
   Last modifiedVulnerability information updated.

Description

OpenTelemetry-Go is the Go implementation of OpenTelemetry. Prior to version 0.21.0, the exporters/otlp/otlplog/otlploggrpc package loads OTEL_EXPORTER_OTLP_LOGS_CERTIFICATE, OTEL_EXPORTER_OTLP_CERTIFICATE, and related client certificate environment variables through loadEnvTLS into cfg.tlsCfg, but newGRPCDialOptions does not apply cfg.tlsCfg when creating gRPC transport credentials. The environment-only TLS path instead uses credentials.NewTLS with system roots and no configured client certificate, bypassing intended private CA pinning and mutual TLS unless the application also supplies WithTLSCredentials. A network attacker able to intercept or spoof the collector connection with a system-trusted certificate can read or alter log telemetry. This issue is fixed in version 0.21.0.

• CWE-295Improper Certificate ValidationThe product does not validate, or incorrectly validates, a certificate.
• CWE-923Improper Restriction of Communication Channel to Intended EndpointsThe product establishes a communication channel to (or from) an endpoint for privileged or protected operations, but it does not properly ensure that it is communicating with the correct endpoint.