Added validation of \n in $additional_headers of mail()

When $additional_headers of mail() is an array, the same validation as
`\r\n` is now applied to `\n` alone too.

NEWS

@@ -15,6 +15,8 @@ PHP                                                                        NEWS
 
 - Standard:
   . Fixed bug GH-11808 (Live filesystem modified by tests). (nielsdos)
+  . Fixed GH-13402: Added validation of `\n` in `$additional_headers` of `mail()`
+    (SakiTakamachi)
 
 - XML:
   . Fixed bug GH-13517 (Multiple test failures when building with

UPGRADING

@@ -243,6 +243,8 @@ PHP 8.2 UPGRADE NOTES
     objects.
   . mail() function reverts back to the mixed LF and CRLF new lines (behavior
     before PHP 8.0) if mail.mixed_lf_and_crlf INI is on.
+  . When $additional_headers of mail() is an array, the same validation as
+    `\r\n` is now applied to `\n` alone too.
 
 - XML
   . xml_parser_set_option() now actually returns false when attempting to set a

ext/standard/mail.c

@@ -57,7 +57,7 @@
 
 extern zend_long php_getuid(void);
 
-static bool php_mail_build_headers_check_field_value(zval *val)
+static php_mail_header_value_error_type php_mail_build_headers_check_field_value(zval *val)
 {
 	size_t len = 0;
 	zend_string *value = Z_STR_P(val);
@@ -66,20 +66,39 @@ static bool php_mail_build_headers_check_field_value(zval *val)
 	/* https://tools.ietf.org/html/rfc2822#section-2.2.3 */
 	while (len < value->len) {
 		if (*(value->val+len) == '\r') {
+			if (*(value->val+len+1) != '\n') {
+				return CONTAINS_CR_ONLY;
+			}
+
 			if (value->len - len >= 3
-				&&  *(value->val+len+1) == '\n'
 				&& (*(value->val+len+2) == ' '  || *(value->val+len+2) == '\t')) {
 				len += 3;
 				continue;
 			}
-			return FAILURE;
+
+			return CONTAINS_CRLF;
+		}
+		/**
+		 * The RFC does not allow using LF alone for folding. However, LF is
+		 * often treated similarly to CRLF, and there are likely many user
+		 * environments that use LF for folding.
+		 * Therefore, considering such an environment, folding with LF alone
+		 * is allowed.
+		 */
+		if (*(value->val+len) == '\n') {
+			if (value->len - len >= 2
+				&& (*(value->val+len+1) == ' '  || *(value->val+len+1) == '\t')) {
+				len += 2;
+				continue;
+			}
+			return CONTAINS_LF_ONLY;
 		}
 		if (*(value->val+len) == '\0') {
-			return FAILURE;
+			return CONTAINS_NULL;
 		}
 		len++;
 	}
-	return SUCCESS;
+	return NO_HEADER_ERROR;
 }
 
 
@@ -108,9 +127,27 @@ static void php_mail_build_headers_elem(smart_str *s, zend_string *key, zval *va
 				zend_value_error("Header name \"%s\" contains invalid characters", ZSTR_VAL(key));
 				return;
 			}
-			if (php_mail_build_headers_check_field_value(val) != SUCCESS) {
-				zend_value_error("Header \"%s\" has invalid format, or contains invalid characters", ZSTR_VAL(key));
-				return;
+
+			php_mail_header_value_error_type error_type = php_mail_build_headers_check_field_value(val);
+			switch (error_type) {
+				case NO_HEADER_ERROR:
+					break;
+				case CONTAINS_LF_ONLY:
+					zend_value_error("Header \"%s\" contains LF character that is not allowed in the header", ZSTR_VAL(key));
+					return;
+				case CONTAINS_CR_ONLY:
+					zend_value_error("Header \"%s\" contains CR character that is not allowed in the header", ZSTR_VAL(key));
+					return;
+				case CONTAINS_CRLF:
+					zend_value_error("Header \"%s\" contains CRLF characters that are used as a line separator and are not allowed in the header", ZSTR_VAL(key));
+					return;
+				case CONTAINS_NULL:
+					zend_value_error("Header \"%s\" contains NULL character that is not allowed in the header", ZSTR_VAL(key));
+					return;
+				default:
+					// fallback
+					zend_value_error("Header \"%s\" has invalid format, or contains invalid characters", ZSTR_VAL(key));
+					return;
 			}
 			smart_str_append(s, key);
 			smart_str_appendl(s, ": ", 2);

ext/standard/php_mail.h

@@ -49,5 +49,12 @@ do { \
 	} \
 } while(0)
 
+typedef enum {
+	NO_HEADER_ERROR,
+	CONTAINS_LF_ONLY,
+	CONTAINS_CR_ONLY,
+	CONTAINS_CRLF,
+	CONTAINS_NULL
+} php_mail_header_value_error_type;
 
 #endif /* PHP_MAIL_H */

ext/standard/tests/mail/gh13415.phpt

@@ -0,0 +1,52 @@
+--TEST--
+GH-13415 (Added validation of line breaks \n in $additional_headers of mail())
+--INI--
+sendmail_path={MAIL:gh13415.out}
+--FILE--
+<?php
+echo "LF only:\n";
+try {
+    mail('to@example.com', 'Test Subject', 'A Message', ['Reply-To' => "foo@example.com \nCc: hacker@example.com"]);
+} catch (Throwable $e) {
+    echo $e->getMessage()."\n\n";
+}
+
+echo "CR only:\n";
+try {
+    mail('to@example.com', 'Test Subject', 'A Message', ['Reply-To' => "foo@example.com \rCc: hacker@example.com"]);
+} catch (Throwable $e) {
+    echo $e->getMessage()."\n\n";
+}
+
+echo "CRLF:\n";
+try {
+    mail('to@example.com', 'Test Subject', 'A Message', ['Reply-To' => "foo@example.com \r\nCc: hacker@example.com"]);
+} catch (Throwable $e) {
+    echo $e->getMessage()."\n\n";
+}
+
+echo "NULL:\n";
+try {
+    mail('to@example.com', 'Test Subject', 'A Message', ['Reply-To' => "foo@example.com \0Cc: hacker@example.com"]);
+} catch (Throwable $e) {
+    echo $e->getMessage()."\n\n";
+}
+?>
+--CLEAN--
+<?php
+if (file_exists('gh13415.out')) {
+    unlink('gh13415.out');
+}
+?>
+--EXPECTF--
+LF only:
+Header "Reply-To" contains LF character that is not allowed in the header
+
+CR only:
+Header "Reply-To" contains CR character that is not allowed in the header
+
+CRLF:
+Header "Reply-To" contains CRLF characters that are used as a line separator and are not allowed in the header
+
+NULL:
+Header "Reply-To" contains NULL character that is not allowed in the header

ext/standard/tests/mail/mail_basic7.phpt

@@ -258,4 +258,4 @@ Subject: Test Subject
 foo9: %&$#!
 
 A Message
-ValueError: Header "foo10" has invalid format, or contains invalid characters
+ValueError: Header "foo10" contains NULL character that is not allowed in the header