Summary
OpenTelemetry-Go: Log gRPC exporter ignores env TLS certs, bypassing mTLS/pinning
The OTLP log gRPC exporter loads TLS settings from environment variables but does not apply them when creating gRPC transport credentials. Operators who rely on OTEL_EXPORTER_OTLP_LOGS_CERTIFICATE, OTEL_EXPORTER_OTLP_CERTIFICATE, or related client certificate variables for CA pinning or mTLS get a connection that falls back to system roots and omits the env-supplied client certificate. A network attacker who can intercept or spoof the collector connection with a system-trusted certificate can read or alter log telemetry.
Introduced in commit: d99c76f
Details
The affected code is in exporters/otlp/otlplog/otlploggrpc.
newConfig resolves env-based TLS configuration into cfg.tlsCfg at exporters/otlp/otlplog/otlploggrpc/config.go:106-116. The finding also identifies loadEnvTLS at config.go:451-492 as the code that builds a *tls.Config containing RootCAs and client certificates from OTEL_EXPORTER_OTLP[_LOGS]_CERTIFICATE and OTEL_EXPORTER_OTLP[_LOGS]_CLIENT_CERTIFICATE/KEY.
However, newGRPCDialOptions in exporters/otlp/otlplog/otlploggrpc/client.go:83-92 only checks cfg.gRPCCredentials and cfg.insecure. When neither is set, which is the normal env-only TLS configuration path, it uses credentials.NewTLS(nil). That default trusts the host system root CAs and contains no env-supplied client certificate. The finding evidence reports no other tlsCfg use in the package, so env-based CA pinning and mTLS settings are loaded but not enforced.
PoC
The validation artifact contains a ready-to-run test at validation-artifact.zip:./poc_env_tls_ignored_test.go and brief instructions at validation-artifact.zip:./README.md.
From a checkout of pellared/opentelemetry-go at commit d99c76f, with Go module dependencies available:
FINDING_DIR=/path/to/02-e6e2897a969c8191b260f243fbc99ebd-log-grpc-exporter-ignores-env-tls-certs-bypassing-mtls-pinning
cd /path/to/opentelemetry-go
git checkout d99c76f
tar -xOf validation-artifact.tar ./poc_env_tls_ignored_test.go > exporters/otlp/otlplog/otlploggrpc/poc_env_tls_ignored_test.go
cd exporters/otlp/otlplog/otlploggrpc
GO111MODULE=on go test -v -run TestEnvTLSIgnored -count=1
The test generates a private CA and a TLS gRPC logs server certificate signed by that CA. It sets:
OTEL_EXPORTER_OTLP_LOGS_ENDPOINT=https://127.0.0.1:<test-port>
OTEL_EXPORTER_OTLP_LOGS_CERTIFICATE=<temp-dir>/ca.pem
Expected output includes an unknown authority failure for the first export call even though the env certificate points to the server CA, followed by a passing test after the same cfg.tlsCfg is explicitly wired through WithTLSCredentials:
=== RUN TestEnvTLSIgnored
poc_env_tls_ignored_test.go:...: export error (expected due to ignored tlsCfg): ... x509: certificate signed by unknown authority
--- PASS: TestEnvTLSIgnored
PASS
This demonstrates that the env CA is parsed into cfg.tlsCfg but ignored by the default gRPC dial path.
Impact
This is improper TLS certificate validation and endpoint authentication caused by ignoring configured trust material. Users of the OTLP log gRPC exporter who configure TLS, CA pinning, or mTLS through environment variables are impacted when they do not also supply explicit WithTLSCredentials. TLS still occurs with system roots, but the intended private CA pinning and client certificate authentication are bypassed. An attacker with a suitable network position and a system-trusted certificate for the collector endpoint can intercept or tamper with log telemetry that operators expected to be protected by the configured CA or mTLS policy.
Affected versions
Security releases
Kodem intelligence
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Frequently Asked Questions
- What is CVE-2026-81871? CVE-2026-81871 is a medium-severity security vulnerability in go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploggrpc (go), affecting versions < 0.21.0. It is fixed in 0.21.0.
- Which versions of go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploggrpc are affected by CVE-2026-81871? go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploggrpc (go) versions < 0.21.0 is affected.
- Is there a fix for CVE-2026-81871? Yes. CVE-2026-81871 is fixed in 0.21.0. Upgrade to this version or later.
- Is CVE-2026-81871 exploitable, and should I be worried? Whether CVE-2026-81871 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-81871 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-81871? Upgrade
go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploggrpcto 0.21.0 or later.