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perl-security

Name: perl-security
Rating: 4.2 (5 reviews)
Author: Affaan Mustafa

affaan-m/perl-security · Agent Skill

by Affaan Mustafa · single

Published Jun 29, 2026 · Last updated Jul 6, 2026

Provides comprehensive security patterns for Perl applications covering taint mode, input validation, safe file operations, SQL injection prevention, and web security.

SKILL.md

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     = <STDIN>;         # 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($input) {
    print "<div>$input</div>";  # XSS if $input contains <script>
}

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 "<div>Welcome, $username!</div>";  # 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.

---
name: perl-security
description: Provides comprehensive security patterns for Perl applications covering taint mode, input validation, safe file operations, SQL injection prevention, and web 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

```perl
#!/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     = <STDIN>;         # 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

```perl
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

```perl
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

```perl
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.

```perl
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

```perl
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

```perl
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

```perl
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

```perl
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

```perl
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)

```perl
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

```perl
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($input) {
    print "<div>$input</div>";  # XSS if $input contains <script>
}
```

### CSRF Protection

```perl
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

```perl
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

```ini
# .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

```bash
# 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

```perl
# 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 "<div>Welcome, $username!</div>";  # 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.

affaan-m/ECC/tree/main/skills/perl-security commit · 4130457d67

▌
perl-security · sakamoto-family-smile
Secure Perl applications against injection, taint, and web vulnerabilities with validated patterns for input handling, file operations, process execution, and DBI queries.

0
repo stars
▌
secure-code-guardian · jeffallan bundle
Guides implementing authentication, authorization, input validation, and OWASP Top 10 prevention with secure code patterns and validation checkpoints.

10.4k
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api-security · luokai0 bundle
Implements secure API design patterns including authentication, authorization, input validation, rate limiting, and protection against common vulnerabilities.

10
repo stars
▌
security-review · sakamoto-family-smile bundle
Provides a security checklist and code patterns for authentication, input validation, secrets management, SQL injection prevention, XSS, CSRF, rate limiting, and sensitive data handling.

0
repo stars
▌
security-review · github bundle
Scans codebases for security vulnerabilities by reasoning about code context, data flow, and component interactions, covering injection flaws, secrets exposure, authentication issues, and weak cryptography across multiple languages.

36.2k
repo stars
▌
security-review · affaan-m bundle
Provides a comprehensive security checklist and code patterns for authentication, input validation, secrets management, SQL injection prevention, XSS, CSRF, rate limiting, and sensitive data exposure.

226k
repo stars

Frequently asked questions

How do I install the perl-security skill?

Run npx skillmds add affaan-m/perl-security in your terminal (requires Node.js), paste this page's agent-chat prompt into Claude, Cursor, or any MCP-connected agent, or download the SKILL.md file and copy it into your agent's skills directory.

What does the perl-security skill do?

Provides comprehensive security patterns for Perl applications covering taint mode, input validation, safe file operations, SQL injection prevention, and web security. It is listed under Security, Coding & Dev Tools, Secure Coding on SkillMD.

Is perl-security safe to use?

SkillMD's automated safety review verdict for this skill is PASS. Independent scanners report: SkillSpector: WARNING, Skill Scanner: PASS. Capability flags: reads secrets. SkillMD never runs a skill's scripts for you; review the SKILL.md before installing.

Which AI agents work with perl-security?

This skill is tagged as working with Claude Code, Claude.ai, OpenAI Codex. SKILL.md is an open format, so most agents that read a skills directory can load it too.

Is perl-security free to use?

Yes. Installing skills from SkillMD is free, and the skill stays under its author's original license.

Who published perl-security?

Affaan Mustafa (@affaan-m) published this skill. Their other Agent Skills are listed on their SkillMD profile.