Modify rustls' CertificateVerifier, removing the cert revocation logic:
This operation is not done by Android by default and doesn't properly support CRLs (Certificate Revocation Lists) which can be a problem with CAs like Let's Encrypt.
This commit is contained in:
Jorge Martín
committed by
Jorge Martin Espinosa
Jorge Martin Espinosa
parent
3586824a0d
commit
f62030ac5b
+7
-89
@@ -14,7 +14,6 @@ package org.rustls.platformverifier
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import android.annotation.SuppressLint
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import android.content.Context
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import android.net.http.X509TrustManagerExtensions
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import android.os.Build
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import android.util.Log
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import java.io.ByteArrayInputStream
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import java.io.File
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@@ -22,18 +21,13 @@ import java.security.KeyStore
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import java.security.KeyStoreException
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import java.security.MessageDigest
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import java.security.PublicKey
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import java.security.cert.CertPathValidator
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import java.security.cert.CertPathValidatorException
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import java.security.cert.CertificateException
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import java.security.cert.CertificateExpiredException
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import java.security.cert.CertificateFactory
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import java.security.cert.CertificateNotYetValidException
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import java.security.cert.CertificateParsingException
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import java.security.cert.PKIXBuilderParameters
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import java.security.cert.PKIXRevocationChecker
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import java.security.cert.X509Certificate
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import java.util.Date
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import java.util.EnumSet
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import javax.net.ssl.TrustManagerFactory
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import javax.net.ssl.X509TrustManager
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import javax.security.auth.x500.X500Principal
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@@ -298,90 +292,14 @@ internal object CertificateVerifier {
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return VerificationResult(StatusCode.Ok)
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}
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// Try to check the revocation status of the cert, if it is supported.
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// =================================================================================================
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// IMPORTANT! DIFF WITH THE ORIGINAL SOURCES HERE:
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//
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// This is supported at >= API 24, but we're supporting 22 (Android 5) for the best
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// compatibility.
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if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
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// Note:
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//
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// 1. Android does not provide any way only to attempt to validate revocation from cached
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// data like the other platforms do. This means it will always use the network for
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// certificates which had no stapled response.
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//
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// 2: Likely because of 1, Android requires all issued certificates to have some form of
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// revocation included in their authority information. This doesn't work universally as
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// issuing certificates in use may omit authority access information (for example the
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// Let's Encrypt R3 Intermediate Certificate).
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//
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// Given these constraints, the best option is to only check revocation information
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// at the end-entity depth. We will prefer OCSP (to use stapled information if possible).
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// If there is no stapled OCSP response, Android may use the network to attempt to fetch
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// one. If OCSP checking fails, it may fall back to fetching CRLs. We allow "soft"
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// failures, for example transient network errors.
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//
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// In the case of a non-public root, such as an internal CA or self-signed certificate,
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// we opt to skip revocation checks entirely. The only exception is if the server
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// provided stapled OCSP data, which is an explicit signal and won't introduce non-ideal
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// platform behavior when attempting validation.
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//
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// This is because these are cases where a user or administrator has explicitly opted to
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// trust a certificate they (at least believe) have control over. These certificates rarely
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// contain revocation information as well, so these cases don't lose much.
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// See https://github.com/rustls/rustls-platform-verifier/issues/69 as well.
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if (ocspResponse == null && !isKnownRoot(validChain.last())) {
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// Chain validation must have succeeded by this point.
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return VerificationResult(StatusCode.Ok)
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}
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val parameters = PKIXBuilderParameters(keystore, null)
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val validator = CertPathValidator.getInstance("PKIX")
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val revocationChecker = validator.revocationChecker as PKIXRevocationChecker
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revocationChecker.options = EnumSet.of(
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PKIXRevocationChecker.Option.SOFT_FAIL,
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PKIXRevocationChecker.Option.ONLY_END_ENTITY
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)
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// Use the OCSP data `rustls` provided, if present.
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// Its expected that the server only sends revocation data for its own leaf certificate.
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//
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// If this field is set, then Android will use it and skip any networking to
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// attempt a fetch for that certificate. Otherwise, it will attempt to fetch it from the network.
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// Ref: https://cs.android.com/android/platform/superproject/+/master:libcore/ojluni/src/main/java/sun/security/provider/certpath/RevocationChecker.java;l=694
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ocspResponse?.let { providedResponse ->
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revocationChecker.ocspResponses = mapOf(endEntity to providedResponse)
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}
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// Use the custom revocation definition.
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// "Note that when a `PKIXRevocationChecker` is added to `PKIXParameters`, it clones the `PKIXRevocationChecker`;
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// thus any subsequent modifications to the `PKIXRevocationChecker` have no effect."
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// - https://developer.android.com/reference/java/security/cert/PKIXRevocationChecker
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parameters.certPathCheckers = listOf(revocationChecker)
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// "When supplying a revocation checker in this manner, it will be used to check revocation
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// irrespective of the setting of the `RevocationEnabled` flag."
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// - https://developer.android.com/reference/java/security/cert/PKIXRevocationChecker
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parameters.isRevocationEnabled = false
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// Validate the revocation status of the end entity certificate.
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try {
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validator.validate(certFactory.generateCertPath(validChain), parameters)
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} catch (e: CertPathValidatorException) {
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// LetsEncrypt no longer include OCSP information (as OCSP is being deprecated) which Android is not
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// happy with since it *only* tries OCSP by default. We aren't 100% decided on how to fix this yet for real
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// (see https://github.com/rustls/rustls-platform-verifier/pull/179) so for now we implement an out for
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// tests to allow regular maintenance to proceed.
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if (BuildConfig.TEST && e.reason == CertPathValidatorException.BasicReason.UNSPECIFIED) {
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return VerificationResult(StatusCode.Ok)
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}
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return VerificationResult(StatusCode.Revoked, e.toString())
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}
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} else {
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// This is allowed to be skipped since revocation checking is best-effort.
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Log.w(TAG, "did not attempt to validate OCSP due to Android version")
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}
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// We removed the cert revocation checks because Android won't do them by default
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// and supporting them would be quite difficult given CRLs won't work out of the box.
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//
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// See https://github.com/rustls/rustls-platform-verifier/issues/221 for more info.
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// =================================================================================================
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return VerificationResult(StatusCode.Ok)
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}
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