Future-proof HTTPS endpoint identification - #2104
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Netty 4.2 changes the default for hostname verification for TLS clients, so that it is now enabled by default. As a result, clients that rely on the default being _off_ will find themselves unable to disable it. Instead, clients should explicitly configure their desired endpoint identification algorithm in all cases. Since Netty 4.1.112 we also have a convenient method on the `SslContextBuilder` for doing this, so we don't need multiple round-trips through `SSLParameters`. This PR changes the `DefaultSslEngineFactory` to make use of this method, so it always configures the endpoint identification algorithm to match the desired setting of `AsyncHttpClientConfig..isDisableHttpsEndpointIdentificationAlgorithm()`.
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hyperxpro
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Aug 21, 2025
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@hyperxpro I don't have the merge button, so feel free to merge any time. |
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Thanks @chrisvest |
hyperxpro
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Motivation `JsseSslEngineFactory` creates the `SSLEngine` using `sslContext.createSSLEngine(host, port)` but only enables client mode via `setUseClientMode(true)`. It never configures endpoint identification, so a JDK `SSLEngine` does not verify the server hostname during the TLS handshake. As a result, any certificate signed by a trusted CA is accepted regardless of the requested hostname, leaving the connection vulnerable to man-in-the-middle attacks. `DefaultSslEngineFactory` correctly enables hostname verification. This regression was introduced in #2104, which removed the shared `setEndpointIdentificationAlgorithm("HTTPS")` call from `configureSslEngine()` and restored it only in `DefaultSslEngineFactory`, unintentionally leaving the pure JSSE path (used with a user-supplied JDK `SSLContext`) without hostname verification. Modification Update `JsseSslEngineFactory.newSslEngine()` to configure the engine's `SSLParameters` with `setEndpointIdentificationAlgorithm("HTTPS")`, unless `config.isDisableHttpsEndpointIdentificationAlgorithm()` is enabled. This matches the behavior of `DefaultSslEngineFactory` while preserving the documented opt-out. Result Connections created through `JsseSslEngineFactory` with a custom JDK `SSLContext` now perform hostname verification during the TLS handshake, matching the default implementation. Existing opt-out behavior remains unchanged, and the `DefaultSslEngineFactory` path is unaffected.
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Netty 4.2 changes the default for hostname verification for TLS clients, so that it is now enabled by default.
As a result, clients that rely on the default being off will find themselves unable to disable it.
Instead, clients should explicitly configure their desired endpoint identification algorithm in all cases.
Since Netty 4.1.112 we also have a convenient method on the
SslContextBuilderfor doing this, so we don't need multiple round-trips throughSSLParameters.This PR changes the
DefaultSslEngineFactoryto make use of this method, so it always configures the endpoint identification algorithm to match the desired setting ofAsyncHttpClientConfig..isDisableHttpsEndpointIdentificationAlgorithm().