perl-security

Perl Security Patterns Comprehensive security guidelines for Perl applications covering input validation, injection prevention, and secure coding practices. When to Activate Handling user input in Perl applications Building Perl web applications (CGI, Mojolicious, Dancer2, Catalyst) Reviewing Perl code for security vulnerabilities Performing file operations with user-supplied paths Executing system commands from Perl Writing DBI database queries How It Works Start with taint-aware input boundaries, then move outward: validate and untaint inputs, keep filesystem and process execution constrained, and use parameterized DBI queries everywhere. The examples below show the safe defaults this skill expects you to apply before shipping Perl code that touches user input, the shell, or the network. Taint Mode Perl's taint mode (-T) tracks data from external sources and prevents it from being used in unsafe operations without explicit validation. Enabling Taint Mode #!/usr/bin/perl -T use v5.36; # Tainted: anything from outside the program my $input = $ARGV[0]; # Tainted my $env_path = $ENV{PATH}; # Tainted my $form = ; # Tainted my $query = $ENV{QUERY_STRING}; # Tainted # Sanitize PATH early (required in taint mode) $ENV{PATH} = '/usr/local/bin:/usr/bin:/bin'; delete @ENV{qw(IFS CDPATH ENV BASH_ENV)}; Untainting Pattern use v5.36; # Good: Validate and untaint with a specific regex sub untaint_username($input) { if ($input =~ /^([a-zA-Z0-9_]{3,30})$/) { return $1; # $1 is untainted } die "Invalid username: must be 3-30 alphanumeric characters\n"; } # Good: Validate and untaint a file path sub untaint_filename($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 $1; # Accepts ANYTHING — pointless } Input Validation Allowlist Over Blocklist use v5.36; # Good: Allowlist — define exactly what's permitted sub validate_sort_field($field) { my %allowed = map { $ => 1 } qw(name email created_at updated_at); die "Invalid sort field: $field\n" unless $allowed{$field}; return $field; } # Good: Validate with specific patterns sub validate_email($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 $1 + 0; # Coerce to number } die "Invalid integer\n"; } # Bad: Blocklist — always incomplete sub bad_validate($input) { die "Invalid" if $input =~ /[<>"';&|]/; # Misses encoded attacks return $input; } Length Constraints use v5.36; sub validate_comment($text) { die "Comment is required\n" unless length($text) > 0; die "Comment exceeds 10000 chars\n" if length($text) > 10_000; return $text; } Safe Regular Expressions ReDoS Prevention Catastrophic backtracking occurs with nested quantifiers on overlapping patterns. use v5.36; # Bad: Vulnerable to ReDoS (exponential backtracking) my $bad_re = qr/^(a+)+$/; # Nested quantifiers my $bad_re2 = qr/^([a-zA-Z]+)$/; # Nested quantifiers on class my $bad_re3 = qr/^(.?,){10,}$/; # Repeated greedy/lazy combo # Good: Rewrite without nesting my $good_re = qr/^a+$/; # Single quantifier my $good_re2 = qr/^[a-zA-Z]+$/; # Single quantifier on class # Good: Use possessive quantifiers or atomic groups to prevent backtracking my $safe_re = qr/^[a-zA-Z]++$/; # Possessive (5.10+) my $safe_re2 = qr/^(?>a+)$/; # Atomic group # Good: Enforce timeout on untrusted patterns use 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 $matched; } Safe File Operations Three-Argument Open use v5.36; # Good: Three-arg open, lexical filehandle, check return sub read_file($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, "< $path"; # Shell metacharacter injection } TOCTOU Prevention and Path Traversal use v5.36; use Fcntl qw(:DEFAULT :flock); use File::Spec; use Cwd qw(realpath); # Atomic file creation sub create_file_safe($path) { sysopen(my $fh, $path, O_WRONLY | O_CREAT | O_EXCL, 0600) or die "Cannot create '$path': $!\n"; return $fh; } # Validate path stays within allowed directory sub safe_path($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 File::Temp for temporary files (tempfile(UNLINK => 1)) and flock(LOCK_EX) to prevent race conditions. Safe Process Execution List-Form system and exec use v5.36; # Good: List form — no shell interpolation sub run_command(@cmd) { system(@cmd) == 0 or die "Command failed: @cmd\n"; } run_command('grep', '-r', $user_pattern, '/var/log/app/'); # Good: Capture output safely with IPC::Run3 use IPC::Run3; sub capture_output(@cmd) { my ($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 interpolation my $output = ls $user_dir; # Shell injection risk Also use Capture::Tiny for capturing stdout/stderr from external commands safely. SQL Injection Prevention DBI Placeholders use v5.36; use DBI; my $dbh = DBI->connect($dsn, $user, $pass, { RaiseError => 1, PrintError => 0, AutoCommit => 1, }); # Good: Parameterized queries — always use placeholders sub find_user($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 $sth->fetchrow_hashref; } Dynamic Column Allowlists use v5.36; # Good: Validate column names against an allowlist sub order_by($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 $sth->fetchall_arrayref({}); } # Bad: Directly interpolating user-chosen column sub bad_order($dbh, $column) { $dbh->prepare("SELECT * FROM users ORDER BY $column"); # SQLi! } DBIx::Class (ORM Safety) use v5.36; # DBIx::Class generates safe parameterized queries my @users = $schema->resultset('User')->search({ status => 'active', email => { -like => '%@example.com' }, }, { order_by => { -asc => 'name' }, rows => 50, }); Web Security XSS Prevention use v5.36; use HTML::Entities qw(encode_entities); use URI::Escape qw(uri_escape_utf8); # Good: Encode output for HTML context sub safe_html($user_input) { return encode_entities($user_input); } # Good: Encode for URL context sub safe_url_param($value) { return uri_escape_utf8($value); } # Good: Encode for JSON context use JSON::MaybeXS qw(encode_json); sub safe_json($data) { return encode_json($data); # Handles escaping } # Template auto-escaping (Mojolicious) # <%= $user_input %> — auto-escaped (safe) # <%== $raw_html %> — raw output (dangerous, use only for trusted content) # Template auto-escaping (Template Toolkit) # [% user_input | html %] — explicit HTML encoding # Bad: Raw output in HTML sub bad_html($input) { print "$input"; # XSS if $input contains } CSRF Protection use v5.36; use Crypt::URandom qw(urandom); use MIME::Base64 qw(encode_base64url); sub generate_csrf_token() { return encode_base64url(urandom(32)); } Use constant-time comparison when verifying tokens. Most web frameworks (Mojolicious, Dancer2, Catalyst) provide built-in CSRF protection — prefer those over hand-rolled solutions. Session and Header Security 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'); }); Output Encoding Always encode output for its context: HTML::Entities::encode_entities() for HTML, URI::Escape::uri_escape_utf8() for URLs, JSON::MaybeXS::encode_json() for JSON. CPAN Module Security Pin versions in cpanfile: requires 'DBI', '== 1.643'; Prefer maintained modules: Check MetaCPAN for recent releases Minimize dependencies: Each dependency is an attack surface Security Tooling perlcritic Security Policies # .perlcriticrc — security-focused configuration severity = 3 theme = security + core # Require three-arg open [InputOutput::RequireThreeArgOpen] severity = 5 # Require checked system calls [InputOutput::RequireCheckedSyscalls] functions = :builtins severity = 4 # Prohibit string eval [BuiltinFunctions::ProhibitStringyEval] severity = 5 # Prohibit backtick operators [InputOutput::ProhibitBacktickOperators] severity = 4 # Require taint checking in CGI [Modules::RequireTaintChecking] severity = 5 # Prohibit two-arg open [InputOutput::ProhibitTwoArgOpen] severity = 5 # Prohibit bare-word filehandles [InputOutput::ProhibitBarewordFileHandles] severity = 5 Running perlcritic # Check a file perlcritic --severity 3 --theme security lib/MyApp/Handler.pm # Check entire project perlcritic --severity 3 --theme security lib/ # CI integration perlcritic --severity 4 --theme security --quiet lib/ || exit 1 Quick Security Checklist Check What to Verify Taint mode -T flag on CGI/web scripts Input validation Allowlist patterns, length limits File operations Three-arg open, path traversal checks Process execution List-form system, no shell interpolation SQL queries DBI placeholders, never interpolate HTML output encode_entities(), template auto-escape CSRF tokens Generated, verified on state-changing requests Session config Secure, HttpOnly, SameSite cookies HTTP headers CSP, X-Frame-Options, HSTS Dependencies Pinned versions, audited modules Regex safety No nested quantifiers, anchored patterns Error messages No stack traces or paths leaked to users Anti-Patterns # 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 sanitizing my $path = $ENV{UPLOAD_DIR}; # Could be manipulated system("ls $path"); # Double vulnerability # 6. Disabling taint without validation ($input) = $input =~ /(.*)/s; # Lazy untaint — defeats purpose # 7. Raw user data in HTML print "Welcome, $username!"; # XSS # 8. Unvalidated redirects print $cgi->redirect($user_url); # Open redirect Remember: Perl's flexibility is powerful but requires discipline. Use taint mode for web-facing code, validate all input with allowlists, use DBI placeholders for every query, and encode all output for its context. Defense in depth — never rely on a single layer.Weekly Installs213Repositoryaffaan-m/everyt…ude-codeGitHub Stars83.1KFirst Seen7 days agoSecurity AuditsGen Agent Trust HubPassSocketPassSnykPassInstalled oncodex201cursor168opencode167github-copilot167amp167cline167