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fix(encryption): read alg/enc exclusively from protected header in JWEDecrypter #658

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fix(encryption): read alg/enc exclusively from protected header in JWEDecrypter #658

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34 changes: 25 additions & 9 deletions src/Library/Encryption/JWEDecrypter.php
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Original file line number Diff line number Diff line change
Expand Up @@ -124,8 +124,12 @@ private function decryptRecipientKey(
);
$this->checkCompleteHeader($completeHeader);

$key_encryption_algorithm = $this->getKeyEncryptionAlgorithm($completeHeader);
$content_encryption_algorithm = $this->getContentEncryptionAlgorithm($completeHeader);
// RFC 7516 §4.1.1 (alg) and §4.1.2 (enc) require both parameters to be
// integrity-protected. Reading them from the merged $completeHeader allows
// an attacker to override either value via an unprotected header field.
$sharedProtectedHeader = $jwe->getSharedProtectedHeader();
$key_encryption_algorithm = $this->getKeyEncryptionAlgorithm($sharedProtectedHeader);
$content_encryption_algorithm = $this->getContentEncryptionAlgorithm($sharedProtectedHeader);

$this->checkIvSize($jwe->getIV(), $content_encryption_algorithm->getIVSize());

Expand Down Expand Up @@ -253,26 +257,38 @@ private function checkCompleteHeader(array $completeHeaders): void
}
}

private function getKeyEncryptionAlgorithm(array $completeHeaders): KeyEncryptionAlgorithm
private function getKeyEncryptionAlgorithm(array $protectedHeader): KeyEncryptionAlgorithm
{
$key_encryption_algorithm = $this->keyEncryptionAlgorithmManager->get($completeHeaders['alg']);
$alg = $protectedHeader['alg'] ?? null;
if (! is_string($alg) || $alg === '') {
throw new InvalidArgumentException(
'The "alg" parameter must be a non-empty string in the protected header (RFC 7516 §4.1.1).'
);
}
$key_encryption_algorithm = $this->keyEncryptionAlgorithmManager->get($alg);
if (! $key_encryption_algorithm instanceof KeyEncryptionAlgorithm) {
throw new InvalidArgumentException(sprintf(
'The key encryption algorithm "%s" is not supported or does not implement KeyEncryptionAlgorithm interface.',
$completeHeaders['alg']
$alg
));
}

return $key_encryption_algorithm;
}

private function getContentEncryptionAlgorithm(array $completeHeader): ContentEncryptionAlgorithm
private function getContentEncryptionAlgorithm(array $protectedHeader): ContentEncryptionAlgorithm
{
$content_encryption_algorithm = $this->contentEncryptionAlgorithmManager->get($completeHeader['enc']);
$enc = $protectedHeader['enc'] ?? null;
if (! is_string($enc) || $enc === '') {
throw new InvalidArgumentException(
'The "enc" parameter must be a non-empty string in the protected header (RFC 7516 §4.1.2).'
);
}
$content_encryption_algorithm = $this->contentEncryptionAlgorithmManager->get($enc);
if (! $content_encryption_algorithm instanceof ContentEncryptionAlgorithm) {
throw new InvalidArgumentException(sprintf(
'The key encryption algorithm "%s" is not supported or does not implement the ContentEncryption interface.',
$completeHeader['enc']
'The content encryption algorithm "%s" is not supported or does not implement the ContentEncryption interface.',
$enc
));
}

Expand Down
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