When you see entries like Invalid method in request \\x16\\x03\\x01 or garbled strings in Apache's error_log, you're witnessing failed SSL/TLS handshake attempts. These binary-looking sequences are actually SSL/TLS protocol headers, not HTTP requests.

// Example of what the raw byte sequence represents:
\x16\x03\x01\x00\xXX  // SSL Record Header (XX = length)
\x01\x00\x00\xXX      // Handshake Header

This occurs when:

• A client attempts SSL/TLS negotiation on a plain HTTP port
• Bots/scanners probing for vulnerable SSL services
• Misconfigured clients trying HTTPS on HTTP ports

To analyze these requests in detail, enable mod_dumpio:

# In httpd.conf or virtual host:
LogLevel dumpio:trace7
DumpIOInput On
DumpIOOutput On

Sample output interpretation:

# SSLv3/TLS Client Hello:
[timestamp] [dumpio:trace7] mod_dumpio: dumpio_in (data-HEAP): 16 03 01 00 b3 01 00 00 af 03 03 [...]

For security-conscious setups:

# Create a separate SSL-only virtual host
<VirtualHost *:443>
    SSLEngine on
    # Redirect HTTP to HTTPS
    RewriteEngine On
    RewriteCond %{HTTPS} off
    RewriteRule (.*) https://%{HTTP_HOST}%{REQUEST_URI}
</VirtualHost>

For debugging:

# Use openssl to simulate the handshake
openssl s_client -connect yourserver:443 -debug

For servers handling both HTTP and HTTPS, implement protocol detection:

# In mod_rewrite rules
RewriteCond %{SERVER_PORT} ^80$
RewriteCond %{REQUEST_URI} !^/server-status
RewriteCond %{REQUEST_METHOD} !^(GET|HEAD|POST|PUT|DELETE)$
RewriteRule .* - [F]

Finding gibberish like \x16\x03\x01 in your Apache error logs typically indicates SSL/TLS handshake attempts. These aren't actual errors, but rather connection attempts that don't complete the HTTP protocol handshake.

The sequence \x16\x03\x01 breaks down as:

\x16 - Content Type (22 = Handshake)
\x03 - SSL Version Major (3)
\x01 - SSL Version Minor (1) = TLS 1.0

This is the start of a TLS ClientHello message, not an HTTP request.

You'll see this when:

1. Port scanners hitting port 443
2. Misconfigured clients attempting TLS on HTTP ports
3. Legacy systems using outdated protocols
4. Botnet probing activity

For Apache 2.4+, add this to your SSL virtual host:

<VirtualHost *:443>
    SSLProtocol all -SSLv3 -TLSv1 -TLSv1.1
    SSLCipherSuite HIGH:!aNULL:!MD5:!RC4:!3DES
    SSLHonorCipherOrder on
    ErrorLog ${APACHE_LOG_DIR}/ssl_error.log
    LogLevel warn
</VirtualHost>

Create a separate error log for SSL handshake failures:

CustomLog logs/ssl_access_log "%t %h %{SSL_PROTOCOL}x %{SSL_CIPHER}x"
ErrorLog logs/ssl_error_log
LogLevel info:ssl_engine:error

Use mod_evasive to block repeated handshake failures:

<IfModule mod_evasive24.c>
    DOSHashTableSize 3097
    DOSPageCount 2
    DOSSiteCount 50
    DOSPageInterval 1
    DOSSiteInterval 1
    DOSBlockingPeriod 60
</IfModule>

Create a log analysis script to track these events:

#!/usr/bin/perl
use strict;
my %client_counts;
while(<>) {
    if(/Invalid method.*\\x16\\x03\\x01.*client (\d+\.\d+\.\d+\.\d+)/) {
        $client_counts{$1}++;
    }
}
foreach my $ip (sort {$client_counts{$b} <=> $client_counts{$a}} keys %client_counts) {
    print "$ip: $client_counts{$ip} attempts\n";
}