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[OTLP] refactor: trust custom CA only #6804

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Merged
rajkumar-rangaraj merged 1 commit into from
Jan 8, 2026
Merged

[OTLP] refactor: trust custom CA only #6804

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60 changes: 31 additions & 29 deletions src/OpenTelemetry.Exporter.OpenTelemetryProtocol/Implementation/OtlpCertificateManager.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -226,40 +226,42 @@ internal static bool ValidateServerCertificate(
{
try
{
// If there are no SSL policy errors, accept the certificate
if (sslPolicyErrors == SslPolicyErrors.None)
// Fail fast for any non-chain-related SSL policy errors (e.g., name mismatch).
var nonChainErrors = sslPolicyErrors & ~SslPolicyErrors.RemoteCertificateChainErrors;
if (nonChainErrors != SslPolicyErrors.None)
{
return true;
OpenTelemetryProtocolExporterEventSource.Log.MtlsServerCertificateValidationFailed(
serverCert.Subject,
sslPolicyErrors.ToString());
return false;
}

// If the only error is an untrusted root, validate against our CA
if (sslPolicyErrors.HasFlag(SslPolicyErrors.RemoteCertificateChainErrors))
// Always validate against the provided CA to enforce custom trust restrictions.
chain.ChainPolicy.ExtraStore.Clear();
chain.ChainPolicy.CustomTrustStore.Clear();
chain.ChainPolicy.ExtraStore.Add(caCertificate);
chain.ChainPolicy.VerificationFlags =
X509VerificationFlags.AllowUnknownCertificateAuthority;
chain.ChainPolicy.CustomTrustStore.Add(caCertificate);
chain.ChainPolicy.TrustMode = X509ChainTrustMode.CustomRootTrust;
chain.ChainPolicy.RevocationMode = X509RevocationMode.NoCheck;
chain.ChainPolicy.RevocationFlag = X509RevocationFlag.ExcludeRoot;

bool isValid = chain.Build(serverCert);

if (isValid)
{
// Add our CA certificate to the chain
chain.ChainPolicy.ExtraStore.Add(caCertificate);
chain.ChainPolicy.VerificationFlags =
X509VerificationFlags.AllowUnknownCertificateAuthority;
chain.ChainPolicy.CustomTrustStore.Add(caCertificate);
chain.ChainPolicy.TrustMode = X509ChainTrustMode.CustomRootTrust;
chain.ChainPolicy.RevocationMode = X509RevocationMode.NoCheck;
chain.ChainPolicy.RevocationFlag = X509RevocationFlag.ExcludeRoot;

bool isValid = chain.Build(serverCert);

if (isValid)
// Verify that the chain terminates with our CA
var rootCert = chain.ChainElements[^1].Certificate;
if (
string.Equals(
rootCert.Thumbprint,
caCertificate.Thumbprint,
StringComparison.OrdinalIgnoreCase))
{
// Verify that the chain terminates with our CA
var rootCert = chain.ChainElements[^1].Certificate;
if (
string.Equals(
rootCert.Thumbprint,
caCertificate.Thumbprint,
StringComparison.OrdinalIgnoreCase))
{
OpenTelemetryProtocolExporterEventSource.Log.MtlsServerCertificateValidated(
serverCert.Subject);
return true;
}
OpenTelemetryProtocolExporterEventSource.Log.MtlsServerCertificateValidated(
serverCert.Subject);
return true;
}
}

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18 changes: 18 additions & 0 deletions test/OpenTelemetry.Exporter.OpenTelemetryProtocol.Tests/OtlpSecureHttpClientFactoryTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -257,6 +257,24 @@ public void ValidateServerCertificate_ReturnsFalse_WhenCaDoesNotMatch()
Assert.False(result);
}

[Fact]
public void ValidateServerCertificate_ReturnsFalse_WhenCaDoesNotMatch_EvenIfSslPolicyErrorsNone()
{
using var caCertificate = CreateCertificateAuthority();
using var otherCaCertificate = CreateCertificateAuthority();
using var serverCertificate = CreateServerCertificate(caCertificate);
using var chain = new X509Chain();
chain.ChainPolicy.RevocationMode = X509RevocationMode.NoCheck;

var result = OpenTelemetryProtocol.Implementation.OtlpCertificateManager.ValidateServerCertificate(
serverCertificate,
chain,
SslPolicyErrors.None,
otherCaCertificate);

Assert.False(result);
}

[Fact]
public void ValidateCertificateChain_ReturnsFalseForExpiredCertificate()
{
Expand Down