Perl Security

#!/usr/bin/perl -Tuse v5.36;
# Tainted: anything from outside the programmy $input    = $ARGV[0];        # Taintedmy $env_path = $ENV{PATH};      # Taintedmy $form     = <STDIN>;         # Taintedmy $query    = $ENV{QUERY_STRING}; # Tainted
# Sanitize PATH early (required in taint mode)$ENV{PATH} = '/usr/local/bin:/usr/bin:/bin';delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};

use v5.36;
# Good: Validate and untaint with a specific regexsub untaint_username($input) {    if ($input =~ /^([a-zA-Z0-9_]{3,30})$/) {        return $1;  # $1 is untainted    }    die "Invalid username: must be 3-30 alphanumeric characters\n";}
# Good: Validate and untaint a file pathsub untaint_filename($input) {    if ($input =~ m{^([a-zA-Z0-9._-]+)$}) {        return $1;    }    die "Invalid filename: contains unsafe characters\n";}
# Bad: Overly permissive untainting (defeats the purpose)sub bad_untaint($input) {    $input =~ /^(.*)$/s;    return $1;  # Accepts ANYTHING — pointless}

use v5.36;
# Good: Allowlist — define exactly what's permittedsub validate_sort_field($field) {    my %allowed = map { $_ => 1 } qw(name email created_at updated_at);    die "Invalid sort field: $field\n" unless $allowed{$field};    return $field;}
# Good: Validate with specific patternssub validate_email($email) {    if ($email =~ /^([a-zA-Z0-9._%+-]+\@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,})$/) {        return $1;    }    die "Invalid email address\n";}
sub validate_integer($input) {    if ($input =~ /^(-?\d{1,10})$/) {        return $1 + 0;  # Coerce to number    }    die "Invalid integer\n";}
# Bad: Blocklist — always incompletesub bad_validate($input) {    die "Invalid" if $input =~ /[<>"';&|]/;  # Misses encoded attacks    return $input;}

use v5.36;
sub validate_comment($text) {    die "Comment is required\n"        unless length($text) > 0;    die "Comment exceeds 10000 chars\n" if length($text) > 10_000;    return $text;}

use v5.36;
# Bad: Vulnerable to ReDoS (exponential backtracking)my $bad_re = qr/^(a+)+$/;           # Nested quantifiersmy $bad_re2 = qr/^([a-zA-Z]+)*$/;   # Nested quantifiers on classmy $bad_re3 = qr/^(.*?,){10,}$/;    # Repeated greedy/lazy combo
# Good: Rewrite without nestingmy $good_re = qr/^a+$/;             # Single quantifiermy $good_re2 = qr/^[a-zA-Z]+$/;     # Single quantifier on class
# Good: Use possessive quantifiers or atomic groups to prevent backtrackingmy $safe_re = qr/^[a-zA-Z]++$/;             # Possessive (5.10+)my $safe_re2 = qr/^(?>a+)$/;                # Atomic group
# Good: Enforce timeout on untrusted patternsuse POSIX qw(alarm);sub safe_match($string, $pattern, $timeout = 2) {    my $matched;    eval {        local $SIG{ALRM} = sub { die "Regex timeout\n" };        alarm($timeout);        $matched = $string =~ $pattern;        alarm(0);    };    alarm(0);    die $@ if $@;    return $matched;}

use v5.36;
# Good: Three-arg open, lexical filehandle, check returnsub read_file($path) {    open my $fh, '<:encoding(UTF-8)', $path        or die "Cannot open '$path': $!\n";    local $/;    my $content = <$fh>;    close $fh;    return $content;}
# Bad: Two-arg open with user data (command injection)sub bad_read($path) {    open my $fh, $path;        # If $path = "|rm -rf /", runs command!    open my $fh, "< $path";   # Shell metacharacter injection}

use v5.36;use Fcntl qw(:DEFAULT :flock);use File::Spec;use Cwd qw(realpath);
# Atomic file creationsub create_file_safe($path) {    sysopen(my $fh, $path, O_WRONLY | O_CREAT | O_EXCL, 0600)        or die "Cannot create '$path': $!\n";    return $fh;}
# Validate path stays within allowed directorysub safe_path($base_dir, $user_path) {    my $real = realpath(File::Spec->catfile($base_dir, $user_path))        // die "Path does not exist\n";    my $base_real = realpath($base_dir)        // die "Base dir does not exist\n";    die "Path traversal blocked\n" unless $real =~ /^\Q$base_real\E(?:\/|\z)/;    return $real;}

use v5.36;
# Good: List form — no shell interpolationsub run_command(@cmd) {    system(@cmd) == 0        or die "Command failed: @cmd\n";}
run_command('grep', '-r', $user_pattern, '/var/log/app/');
# Good: Capture output safely with IPC::Run3use IPC::Run3;sub capture_output(@cmd) {    my ($stdout, $stderr);    run3(\@cmd, \undef, \$stdout, \$stderr);    if ($?) {        die "Command failed (exit $?): $stderr\n";    }    return $stdout;}
# Bad: String form — shell injection!sub bad_search($pattern) {    system("grep -r '$pattern' /var/log/app/");  # If $pattern = "'; rm -rf / #"}
# Bad: Backticks with interpolationmy $output = `ls $user_dir`;   # Shell injection risk

use v5.36;use DBI;
my $dbh = DBI->connect($dsn, $user, $pass, {    RaiseError => 1,    PrintError => 0,    AutoCommit => 1,});
# Good: Parameterized queries — always use placeholderssub find_user($dbh, $email) {    my $sth = $dbh->prepare('SELECT * FROM users WHERE email = ?');    $sth->execute($email);    return $sth->fetchrow_hashref;}
sub search_users($dbh, $name, $status) {    my $sth = $dbh->prepare(        'SELECT * FROM users WHERE name LIKE ? AND status = ? ORDER BY name'    );    $sth->execute("%$name%", $status);    return $sth->fetchall_arrayref({});}
# Bad: String interpolation in SQL (SQLi vulnerability!)sub bad_find($dbh, $email) {    my $sth = $dbh->prepare("SELECT * FROM users WHERE email = '$email'");    # If $email = "' OR 1=1 --", returns all users    $sth->execute;    return $sth->fetchrow_hashref;}

use v5.36;
# Good: Validate column names against an allowlistsub order_by($dbh, $column, $direction) {    my %allowed_cols = map { $_ => 1 } qw(name email created_at);    my %allowed_dirs = map { $_ => 1 } qw(ASC DESC);
    die "Invalid column: $column\n"    unless $allowed_cols{$column};    die "Invalid direction: $direction\n" unless $allowed_dirs{uc $direction};
    my $sth = $dbh->prepare("SELECT * FROM users ORDER BY $column $direction");    $sth->execute;    return $sth->fetchall_arrayref({});}
# Bad: Directly interpolating user-chosen columnsub bad_order($dbh, $column) {    $dbh->prepare("SELECT * FROM users ORDER BY $column");  # SQLi!}

use v5.36;
# DBIx::Class generates safe parameterized queriesmy @users = $schema->resultset('User')->search({    status => 'active',    email  => { -like => '%@example.com' },}, {    order_by => { -asc => 'name' },    rows     => 50,});

use v5.36;use HTML::Entities qw(encode_entities);use URI::Escape qw(uri_escape_utf8);
# Good: Encode output for HTML contextsub safe_html($user_input) {    return encode_entities($user_input);}
# Good: Encode for URL contextsub safe_url_param($value) {    return uri_escape_utf8($value);}
# Good: Encode for JSON contextuse JSON::MaybeXS qw(encode_json);sub safe_json($data) {    return encode_json($data);  # Handles escaping}
# Template auto-escaping (Mojolicious)# <%= $user_input %>   — auto-escaped (safe)# <%== $raw_html %>    — raw output (dangerous, use only for trusted content)
# Template auto-escaping (Template Toolkit)# [% user_input | html %]  — explicit HTML encoding
# Bad: Raw output in HTMLsub bad_html($input) {    print "<div>$input</div>";  # XSS if $input contains <script>}

use v5.36;use Crypt::URandom qw(urandom);use MIME::Base64 qw(encode_base64url);
sub generate_csrf_token() {    return encode_base64url(urandom(32));}

use v5.36;
# Mojolicious session + headers$app->secrets(['long-random-secret-rotated-regularly']);$app->sessions->secure(1);          # HTTPS only$app->sessions->samesite('Lax');
$app->hook(after_dispatch => sub ($c) {    $c->res->headers->header('X-Content-Type-Options' => 'nosniff');    $c->res->headers->header('X-Frame-Options'        => 'DENY');    $c->res->headers->header('Content-Security-Policy' => "default-src 'self'");    $c->res->headers->header('Strict-Transport-Security' => 'max-age=31536000; includeSubDomains');});

# 1. Two-arg open with user data (command injection)open my $fh, $user_input;               # CRITICAL vulnerability
# 2. String-form system (shell injection)system("convert $user_file output.png"); # CRITICAL vulnerability
# 3. SQL string interpolation$dbh->do("DELETE FROM users WHERE id = $id");  # SQLi
# 4. eval with user input (code injection)eval $user_code;                         # Remote code execution
# 5. Trusting $ENV without sanitizingmy $path = $ENV{UPLOAD_DIR};             # Could be manipulatedsystem("ls $path");                      # Double vulnerability
# 6. Disabling taint without validation($input) = $input =~ /(.*)/s;           # Lazy untaint — defeats purpose
# 7. Raw user data in HTMLprint "<div>Welcome, $username!</div>";  # XSS
# 8. Unvalidated redirectsprint $cgi->redirect($user_url);         # Open redirect