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Fix isAscii returning true for malformed surrogates #9261

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Fix isAscii returning true for malformed surrogates #9261

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27f3faf
Fix isAscii returning true for malformed surrogates
one-kash Jan 21, 2026
0820395
Merge branch 'master' into fix/6357-isascii-malformed-surrogates
yschimke Feb 5, 2026
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3 changes: 1 addition & 2 deletions okhttp/src/commonJvmAndroid/kotlin/okhttp3/internal/tls/OkHostnameVerifier.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -24,7 +24,6 @@ import javax.net.ssl.SSLException
import javax.net.ssl.SSLSession
import okhttp3.internal.canParseAsIpAddress
import okhttp3.internal.toCanonicalHost
import okio.utf8Size

/**
* A HostnameVerifier consistent with [RFC 2818][rfc_2818].
Expand Down Expand Up @@ -96,7 +95,7 @@ object OkHostnameVerifier : HostnameVerifier {
}

/** Returns true if the [String] is ASCII encoded (0-127). */
private fun String.isAscii() = length == utf8Size().toInt()
private fun String.isAscii() = all { it.code <= 127 }
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@yschimke yschimke Jan 25, 2026

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I suspect we want to avoid Iterable.all to avoid an allocation.


/**
* Returns true if [hostname] matches the domain name [pattern].
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27 changes: 27 additions & 0 deletions okhttp/src/jvmTest/kotlin/okhttp3/internal/tls/HostnameVerifierTest.kt
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Expand Up @@ -803,6 +803,33 @@ class HostnameVerifierTest {
assertThat(localVerifier.verify("\uD83D\uDCA9.com", session)).isFalse()
}

/**
* Test that malformed surrogates (unpaired high/low surrogates) are correctly
* identified as non-ASCII and rejected.
*
* https://github.com/square/okhttp/issues/6357
*/
@Test fun malformedSurrogatesAreNotAscii() {
val heldCertificate =
HeldCertificate
.Builder()
.commonName("Foo Corp")
.addSubjectAlternativeName("foo.com")
.build()
val session = session(heldCertificate.certificatePem())

// Unpaired high surrogate - should not match any hostname
assertThat(verifier.verify("\uD800.com", session)).isFalse()
assertThat(verifier.verify("foo\uD800.com", session)).isFalse()

// Unpaired low surrogate - should not match any hostname
assertThat(verifier.verify("\uDC00.com", session)).isFalse()
assertThat(verifier.verify("foo\uDC00.com", session)).isFalse()
Comment on lines +821 to +827
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@yschimke yschimke Jan 25, 2026

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Would any of these have matched before the change? is there some case where length == utf8Size().toInt() would match because of offsetting issues, longer lower case, and malformed surrogate.


// Valid hostname should still work
assertThat(verifier.verify("foo.com", session)).isTrue()
}

@Test fun verifyAsIpAddress() {
// IPv4
assertThat("127.0.0.1".canParseAsIpAddress()).isTrue()
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