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Log gRPC exporter ignores env TLS certs, bypassing mTLS/pinning

Moderate
pellared published GHSA-w34q-cm8f-9c5x Sep 2, 2026

Package

gomod go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploggrpc (Go)

Affected versions

< v0.21.0

Patched versions

>= v0.21.0

Description

Summary

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

validation-artifact.zip

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.

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity Low
Attack Requirements Present
Privileges Required None
User interaction None
Vulnerable System Impact Metrics
Confidentiality Low
Integrity Low
Availability None
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N

CVE ID

CVE-2026-81871

Weaknesses

Improper Certificate Validation

The product does not validate, or incorrectly validates, a certificate. Learn more on MITRE.

Improper Restriction of Communication Channel to Intended Endpoints

The 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. Learn more on MITRE.

Credits