NAME

CGI::ACL - Decide whether to allow a client to run a CGI script

VERSION

Version 0.10

SYNOPSIS

CGI::ACL controls who can run your CGI script. You build a set of rules and then call all_denied() on every request. If it returns 1, send an error response or redirect; if it returns 0, allow the request.

Rules can be stacked in any order using method chaining. An unrestricted object (no rules added) allows everything.

Block all cloud-hosted visitors

The simplest use case -- no country list or lingua object needed.

use CGI::ACL;

my $acl = CGI::ACL->new()->deny_cloud();

if ($acl->all_denied()) {
    print "Content-Type: text/plain\n\n";
    print "Automated cloud traffic is not permitted.\n";
    exit;
}

Allow only specific IP addresses or CIDR ranges

Localhost is NOT automatically allowed once any restriction is set. Add it explicitly if your script is called from the same machine.

use CGI::ACL;

my $acl = CGI::ACL->new()
    ->allow_ip('127.0.0.1')        # local machine
    ->allow_ip('203.0.113.0/24')   # office CIDR block
    ->allow_ip('2001:db8::1');     # single IPv6 address

if ($acl->all_denied()) {
    print "Content-Type: text/plain\n\n";
    print "Your IP address is not on the allow list.\n";
    exit;
}

Block visitors from specific countries

Deny mode: allow everyone except the listed countries.

use CGI::Lingua;
use CGI::ACL;

my $lingua = CGI::Lingua->new(supported => ['en']);

my $acl = CGI::ACL->new()
    ->deny_country('CN')
    ->deny_country(country => ['RU', 'KP']);

if ($acl->all_denied(lingua => $lingua)) {
    print "Content-Type: text/plain\n\n";
    print "Access from your country is not permitted.\n";
    exit;
}

Allow only specific countries (allowlist)

Default-deny mode: block everyone except the listed countries. Use deny_all_countries() to turn on default-deny, then list each permitted country with allow_country().

use CGI::Lingua;
use CGI::ACL;

my $lingua = CGI::Lingua->new(supported => ['en', 'de', 'fr']);

my $acl = CGI::ACL->new()
    ->deny_all_countries()
    ->allow_country('GB')
    ->allow_country('US')
    ->allow_country('DE');

if ($acl->all_denied(lingua => $lingua)) {
    print "Content-Type: text/plain\n\n";
    print "This service is available in GB, US, and DE only.\n";
    exit;
}

Production-grade: IP allowlist + country allowlist + cloud block

Combine all three rule types. Rules are evaluated in this fixed order: cloud check, IP check, country check.

use CGI::Lingua;
use CGI::ACL;

my $lingua = CGI::Lingua->new(supported => ['en']);

my $acl = CGI::ACL->new()
    ->deny_cloud()                  # block AWS, GCP, Azure, etc.
    ->allow_ip('127.0.0.1')         # always allow localhost
    ->allow_ip('198.51.100.0/24')   # corporate network
    ->deny_all_countries()          # default-deny all countries...
    ->allow_country('GB')           # ...except UK
    ->allow_country('US');          # ...and US

if ($acl->all_denied(lingua => $lingua)) {
    print "Content-Type: text/plain\n\n";
    print "Access denied.\n";
    exit;
}

Call new() on an existing object to get an independent copy. Changing the copy does not affect the original.

use CGI::ACL;

# Shared base: block cloud for all routes
my $base_acl = CGI::ACL->new()->deny_cloud();

# Admin route: additionally restrict to a single IP
my $admin_acl = $base_acl->new()->allow_ip('198.51.100.1');

if ($admin_acl->all_denied()) {
    print "Content-Type: text/plain\n\n";
    print "Admin access denied.\n";
    exit;
}

The module optionally integrates with CGI::Lingua for country detection. Runtime configuration is supported via Object::Configure.

COMMON PITFALLS

The following mistakes are easy to make. Read this section before filing a bug report.

allow_country alone has no effect

allow_country() only restricts access when default-deny mode is active. Default-deny mode is activated by deny_country('*') or deny_all_countries(). Without it, allow_country() is silently ignored and everyone is still allowed.

# WRONG -- this allows everyone; allow_country is ignored
my $acl = CGI::ACL->new()->allow_country('US');

# RIGHT -- deny all countries first, then add permitted ones
my $acl = CGI::ACL->new()->deny_all_countries()->allow_country('US');

deny_cloud overrides allow_ip

Cloud detection has the highest priority. An IP address that is listed in allow_ip() is still blocked if its reverse DNS resolves to a cloud provider hostname. This is intentional: cloud IPs can be reassigned, so the rDNS check is more reliable than the IP address alone.

# This STILL blocks the IP if it is a cloud host
my $acl = CGI::ACL->new()
    ->deny_cloud()
    ->allow_ip('198.51.100.5');   # blocked if rDNS says EC2

Localhost is not automatically allowed

Once any restriction is set, 127.0.0.1 is subject to the same rules as any other address. If you need to allow local access (for example, a health-check endpoint), add it explicitly.

my $acl = CGI::ACL->new()
    ->allow_ip('127.0.0.1')   # must be explicit
    ->deny_all_countries()
    ->allow_country('US');

Forgetting the lingua argument

When country restrictions are active and all_denied() is called without a lingua argument, the module emits a carp warning and denies the request. Always pass a CGI::Lingua object when country rules are in use.

# WRONG -- will carp and deny every request
my $acl = CGI::ACL->new()->deny_all_countries()->allow_country('US');
$acl->all_denied();

# RIGHT
my $lingua = CGI::Lingua->new(supported => ['en']);
$acl->all_denied(lingua => $lingua);

VPN and proxy users bypass IP and country checks

A visitor who connects through a VPN, Tor exit node, or anonymous proxy will appear to come from the proxy's IP address and country, not their own. CGI::ACL has no way to detect this. Cloud blocking provides some mitigation for VPS-based proxies.

Country codes are case-insensitive but stored lowercase

deny_country('BR') and deny_country('br') are equivalent. All country codes are stored in lowercase. CGI::Lingua::country() may return either case; all_denied() normalises it with lc() before comparing.

The DNS result cache is not shared between CGI requests

In traditional CGI (one process per request), the per-object DNS cache is destroyed at the end of every request. The cache is only useful in persistent-process setups such as FastCGI, mod_perl, or Plack servers, where the same CGI::ACL object survives across many requests.

SUBROUTINES/METHODS

new

Creates and returns a new CGI::ACL object.

When called on an existing object it returns a deep clone of that object, optionally overriding public fields with the supplied arguments. The public data hashes (allowed_ips, deny_countries, allow_countries) are copied so that mutations to the clone do not affect the original. Derived/private keys (_cidrlist, _cloud_cache) are always cleared; they are rebuilt from the cloned public state on the next all_denied() call.

Security note: private _* keys are stripped from all constructor arguments, including those supplied via environment variables or a config file. Accepting _cloud_cache entries from outside the process would allow an attacker with environment-variable access to pre-seed the DNS result cache and bypass deny_cloud() for specific IP addresses.

Constructor arguments may also be supplied via environment variables of the form CGI__ACL__<field> or via a config file; see Object::Configure for details.

EXAMPLE

# No restrictions (allow all by default)
my $acl = CGI::ACL->new();

# Pre-seeded allow list
my $acl = CGI::ACL->new(allowed_ips => { '127.0.0.1' => 1 });

# Clone an existing ACL and add a restriction
my $acl2 = $acl->new(deny_cloud => 1);

API SPECIFICATION

Input

# Compatible with Params::Validate::Strict:
{
    allowed_ips     => { type => 'hashref',  optional => 1 },
    deny_countries  => { type => 'hashref',  optional => 1 },
    allow_countries => { type => 'hashref',  optional => 1 },
    deny_cloud      => { type => 'boolean',  optional => 1 },
}

Output

# Compatible with Return::Set:
{ type => 'object', isa => 'CGI::ACL' }
# or undef when called as CGI::ACL::new() instead of CGI::ACL->new()

MESSAGES

CGI::ACL use ->new() not ::new() to instantiate: Severity: carp (warning). Cause: CGI::ACL::new(...) was called as a plain function instead of as a class method. Action: Change the call to CGI::ACL->new(...).

allow_ip

Adds an IPv4/IPv6 address or CIDR block to the set of explicitly permitted clients. When allowed_ips is non-empty, any client address not matched by an entry in the set is denied (subject to deny_cloud taking precedence).

EXAMPLE

use CGI::ACL;

# Single address
my $acl = CGI::ACL->new()->allow_ip('203.0.113.5');

# Named parameter
my $acl = CGI::ACL->new()->allow_ip(ip => '203.0.113.5');

# CIDR block
my $acl = CGI::ACL->new()->allow_ip(ip => '192.0.2.0/24');

# Method chaining
my $acl = CGI::ACL->new()
    ->allow_ip('192.0.2.1')
    ->allow_ip('10.0.0.0/8');

ARGUMENTS

ip (required): A string containing an IPv4 address, an IPv6 address, or a CIDR block (e.g. 10.0.0.0/8). The format is validated before storage; syntactically invalid values are rejected with a carp warning and the object is returned unchanged.

RETURNS

The object itself, to allow method chaining.

SIDE EFFECTS

On the first call (even if the supplied address is invalid), initialises $self->{allowed_ips} to an empty hashref so that all_denied() treats the ACL as having IP restrictions configured. This ensures fail-closed behaviour: an ACL whose only allow_ip() calls all supplied invalid addresses denies all traffic rather than allowing it.

On a successful (valid) call, also invalidates the internal CIDR lookup cache so the next call to all_denied() rebuilds it with the new entry.

API SPECIFICATION

Input

# Compatible with Params::Validate::Strict:
{
    ip => { type => 'string', regex => qr/\S+/, required => 1 },
}

Output

# Compatible with Return::Set:
{ type => 'object', isa => 'CGI::ACL' }

MESSAGES

Usage: allow_ip($ip_address): Severity: carp (warning). Cause: Called with no argument, with a non-hash reference, or without supplying the ip key. Action: Pass a scalar IP/CIDR string: allow_ip('192.0.2.1') or allow_ip(ip => '192.0.2.1').
allow_ip: 'X' is not a valid IP address or CIDR block: Severity: carp (warning). Cause: The supplied string does not parse as a syntactically valid IPv4 address, IPv6 address, or CIDR block. The value (truncated to 60 chars in the message) was not stored. $self-{allowed_ips}> is still initialised so the ACL remains in fail-closed mode. Action: Check the supplied string for typos. Use dotted-quad notation for IPv4 (e.g. 192.0.2.1), colon-hex for IPv6 (e.g. 2001:db8::1), or slash-notation for CIDR (e.g. 10.0.0.0/8).

deny_country

Adds one or more countries to the deny list. Countries are identified by their ISO 3166-1 alpha-2 codes (case-insensitive).

Passing the special value '*' (wildcard) switches to default-deny mode: all countries are denied unless they also appear in the allow list set by allow_country().

EXAMPLE

use CGI::ACL;

# Deny a single country
my $acl = CGI::ACL->new()->deny_country('BR');

# Deny a list of countries
my $acl = CGI::ACL->new()->deny_country(country => ['BR', 'CN', 'RU']);

# Default-deny all countries (use with allow_country to whitelist)
my $acl = CGI::ACL->new()->deny_country('*')->allow_country('US');

ARGUMENTS

country (required): A scalar ISO code, the wildcard '*', or an array reference of ISO codes.

RETURNS

The object itself, to allow method chaining.

SIDE EFFECTS

Updates $self->{deny_countries}.

NOTES

allow_country() has no effect unless deny_country('*') has been called first. Calling allow_country() alone (without the wildcard deny) does not restrict access.

API SPECIFICATION

Input

# Compatible with Params::Validate::Strict:
{
    country => {
        type     => 'string' | 'arrayref',
        required => 1,
    },
}

Output

# Compatible with Return::Set:
{ type => 'object', isa => 'CGI::ACL' }

MESSAGES

Usage: deny_country($country): Severity: carp (warning). Cause: Called with no argument, with a non-hash/non-array reference, or without supplying the country key. Action: Pass a scalar ISO code or arrayref: deny_country('BR') or deny_country(country => ['BR','CN']).

allow_country

Adds one or more countries to the explicit permit list. This is meaningful only when deny_country('*') has been called first; without the wildcard deny, this method has no observable effect on access decisions.

EXAMPLE

use CGI::ACL;

# Allow only the UK and US
my $acl = CGI::ACL->new()
    ->deny_country('*')
    ->allow_country(country => ['GB', 'US']);

# Single country as positional argument
my $acl = CGI::ACL->new()->deny_country('*')->allow_country('US');

ARGUMENTS

country (required): A scalar ISO code or an array reference of ISO codes.

RETURNS

The object itself, to allow method chaining.

SIDE EFFECTS

Updates $self->{allow_countries}.

NOTES

Call deny_country('*') before this method; otherwise all traffic is already allowed by the default-allow rule and the permit list is never consulted.

API SPECIFICATION

Input

# Compatible with Params::Validate::Strict:
{
    country => {
        type     => 'string' | 'arrayref',
        required => 1,
    },
}

Output

# Compatible with Return::Set:
{ type => 'object', isa => 'CGI::ACL' }

MESSAGES

Usage: allow_country($country): Severity: carp (warning). Cause: Called with no argument, with a non-hash/non-array reference, or without supplying the country key. Action: Pass a scalar ISO code or arrayref: allow_country('US') or allow_country(country => ['GB','US']).

deny_cloud

Enables blocking of requests that originate from major cloud-hosting providers. Detection is performed via verified reverse DNS: the client IP is looked up, the resulting hostname is forward-confirmed to prevent spoofing, and the confirmed hostname is matched against a list of provider-specific patterns.

Covered providers (as of this release): AWS EC2, Google Cloud Compute, Microsoft Azure, DigitalOcean, Linode/Akamai, Hetzner, OVH.

Important: deny_cloud takes precedence over allow_ip. An IP that is explicitly permitted via allow_ip() is still denied if its reverse DNS resolves to a cloud provider hostname.

EXAMPLE

use CGI::ACL;

my $acl = CGI::ACL->new()->deny_cloud();

if ($acl->all_denied()) {
    print "Cloud-hosted clients are not permitted.\n";
    exit;
}

ARGUMENTS

None.

RETURNS

The object itself, to allow method chaining.

SIDE EFFECTS

Sets $self->{deny_cloud} to 1.

NOTES

IPv4 and IPv6 clients are both subject to the cloud check. A client with no reverse DNS record, or whose forward confirmation fails, is treated as a non-cloud host and allowed through the cloud check (though it may still be denied by other rules).

DNS lookups are performed synchronously. On non-Windows platforms a $DNS_TIMEOUT-second alarm is used to prevent indefinite blocking.

API SPECIFICATION

Input

# No parameters accepted.
{}

Output

# Compatible with Return::Set:
{ type => 'object', isa => 'CGI::ACL' }

MESSAGES

This method emits no messages.

deny_all_countries

Convenience method equivalent to deny_country('*'). Switches the ACL into default-deny mode for country checks: every country is denied unless it also appears in the permit list added by allow_country().

This is the idiomatic way to build an allowlist-only country policy without spelling out the wildcard literal.

EXAMPLE

use CGI::ACL;

# Allow only the UK and US; deny every other country
my $acl = CGI::ACL->new()
    ->deny_all_countries()
    ->allow_country('GB')
    ->allow_country('US');

if ($acl->all_denied(lingua => $lingua)) {
    print "Your country is not permitted.\n";
    exit;
}

ARGUMENTS

None.

RETURNS

The object itself, to allow method chaining.

SIDE EFFECTS

Sets $self->{deny_countries}{'*'} to 1, activating default-deny mode. allow_country() calls made before or after this method both take effect - evaluation order is irrelevant because all data is applied at all_denied() call time.

NOTES

allow_country() has no restrictive effect unless this method (or deny_country('*')) has also been called.

API SPECIFICATION

Input

# No parameters accepted.
{}

Output

# Compatible with Return::Set:
{ type => 'object', isa => 'CGI::ACL' }

MESSAGES

This method emits no messages.

all_denied

Evaluates every active restriction against the current client and returns 1 (deny) or 0 (allow).

The evaluation order is:

If no restrictions are configured at all, return 0 (allow).
Validate REMOTE_ADDR as a syntactically correct IPv4 or IPv6 address. If it is missing or malformed, return 1 (deny).
If deny_cloud is set, perform a verified reverse-DNS lookup. If the hostname matches a cloud provider, return 1 (deny) immediately, regardless of allowed_ips. If the IP is not a cloud host and no other restrictions are active, return 0 (allow).
If allowed_ips is set, check the client address against the exact-match hash and then the CIDR list. Return 0 (allow) on a match.
If country restrictions are set, resolve the client's country via the lingua argument. Apply default-deny or default-allow country logic. If no lingua is provided, emit a warning and return 1 (deny).

Note that localhost (127.0.0.1) is not automatically allowed once any restriction is configured; call allow_ip('127.0.0.1') explicitly.

EXAMPLE

use CGI::Lingua;
use CGI::ACL;

my $acl = CGI::ACL->new()->allow_ip('8.35.80.39');

if ($acl->all_denied()) {
    print "You are not allowed to view this site.\n";
    exit;
}

# Country check
my $acl2 = CGI::ACL->new()
    ->deny_country('*')
    ->allow_country('US');

if ($acl2->all_denied(lingua => CGI::Lingua->new(supported => ['en']))) {
    print "US-only site.\n";
    exit;
}

ARGUMENTS

lingua (optional): A CGI::Lingua object (or any object with a country() method returning an ISO 3166-1 alpha-2 code or undef). Required when country restrictions are active; ignored otherwise.

RETURNS

1 if access is denied, 0 if access is allowed.

SIDE EFFECTS

May populate or update $self->{_cidrlist} (the memoised CIDR lookup structure) and $self->{_cloud_cache} (the per-object DNS result cache, keyed by IP address string) as performance optimisations.

API SPECIFICATION

Input

# Compatible with Params::Validate::Strict:
{
    lingua => { type => 'object', optional => 1 },
}

Output

# Compatible with Return::Set:
{ type => 'string', regex => qr/^[01]$/ }

MESSAGES

Usage: all_denied($lingua): Severity: carp (warning). Cause: Country restrictions are active (deny_country or allow_country was called) but no lingua argument was supplied. Action: Pass a CGI::Lingua object: all_denied(lingua => $lingua).

PSEUDOCODE

IF no restrictions configured THEN
    RETURN 0  (allow -- fast path)

raw := REMOTE_ADDR // '127.0.0.1'
-- \A and \z anchors (not ^ / $): \z never matches before a trailing \n
IF raw not matched by /\A IPv4-or-IPv6 \z/ THEN
    RETURN 1  (deny -- bad or injected address)
-- Detaint: extract addr via character-class capture so the value
-- is clean under Perl -T taint mode for all downstream callers
addr := capture [0-9A-Fa-f:.]+ from raw

IF deny_cloud is set THEN
    consult per-object cache keyed by addr (TTL 300 s)
    IF cache miss THEN
        is_cloud := _is_cloud_host(addr)  [DNS; may throw]
        IF no error THEN cache result END IF
    END IF
    IF is_cloud THEN RETURN 1 (deny -- cloud host)
    IF no meaningful further restrictions THEN RETURN 0 (allow)
    -- "meaningful" = allowed_ips ≠ ∅ OR deny_countries ≠ ∅
    -- allow_countries alone is not meaningful (never changes the decision)
END IF

IF allowed_ips is set THEN
    IF addr matches exact-match entry THEN RETURN 0 (allow)
    IF addr falls inside any CIDR range THEN RETURN 0 (allow)
END IF

IF deny_countries is set THEN
    -- Premise: allow_countries alone is vacuous (always returns 0 in
    -- non-wildcard mode); if only allow_countries was set, earlier guards
    -- already returned 0.  This condition is therefore necessary and sufficient.
    IF no lingua supplied THEN carp; RETURN 1 (deny)
    IF lingua is not a blessed object THEN carp; RETURN 1 (deny)
    country := lingua->country()   [wrapped in eval]
    IF country is falsy (undef / "" / "0") THEN RETURN 1 (deny)
    country := lc(country)
    -- Transitive reduction: deny_countries is provably non-nil here.
    IF wildcard (*) in deny_countries THEN
        IF country in allow_countries THEN RETURN 0 (allow)
        ELSE                               RETURN 1 (deny)
    ELSE
        IF country in deny_countries THEN RETURN 1 (deny)
        ELSE                              RETURN 0 (allow)
    END IF
END IF

RETURN 1  (deny -- no rule permitted the request)

AUTHOR

Nigel Horne, <njh at nigelhorne.com>

BUGS

Please report any bugs or feature requests to bug-cgi-acl at rt.cpan.org, or through the web interface at http://rt.cpan.org/NoAuth/ReportBug.html?Queue=CGI-ACL.

A VPN or proxy will most likely bypass IP-based access control.

SUPPORT

perldoc CGI::ACL

MetaCPAN: https://metacpan.org/release/CGI-ACL
RT: https://rt.cpan.org/NoAuth/Bugs.html?Dist=CGI-ACL
CPANTS: http://cpants.cpanauthors.org/dist/CGI-ACL
CPAN Testers: http://matrix.cpantesters.org/?dist=CGI-ACL

LIMITATIONS

A VPN or anonymous proxy will likely bypass IP-based access control and may defeat country detection as well.
Country detection relies on CGI::Lingua and its underlying GeoIP database, which must be updated regularly. GeoIP databases are never fully accurate; satellite and mobile networks in particular can be misattributed.
Cloud detection depends on provider-maintained reverse-DNS records. A cloud host whose PTR record does not follow its provider's naming convention will not be detected. Conversely, a legitimate host whose PTR record accidentally matches a cloud pattern could be falsely denied.
DNS lookups are synchronous. On non-Windows platforms a $DNS_TIMEOUT-second alarm prevents indefinite blocking, but under high resolver load that latency can still affect every request for an uncached IP. For persistent processes (FastCGI, mod_perl) the built-in per-object cache ($CLOUD_CACHE_TTL seconds) mitigates this significantly.
The per-object DNS result cache is neither shared between processes nor persistent across objects. Under a pre-forking server each worker child maintains an independent cache.
Private methods (_is_cloud_host, _verified_rdns, _rdns_forward, _set_countries) are not enforced as private with Sub::Private because this module's white-box test suite (t/function.t, t/extended_tests.t, etc.) calls them directly by fully-qualified name to exercise specific code paths. The namespace::clean pragma removes them from the object's method dispatch table, and the _ naming convention signals their internal nature.
Windows platforms do not support alarm()-based timeouts. DNS lookups on Windows block synchronously for as long as the OS resolver takes.
An optional rate-limiting feature (to block brute-force attacks) has not yet been implemented. It would require persistent shared state (e.g. Redis or an in-memory cache) beyond this module's current dependency set.

FORMAL SPECIFICATION

new

──────────────── ACLState ────────────────────────────────────────
  allowed_ips    : IP_Str ⇸ Bool
  deny_countries : Country ⇸ Bool
  allow_countries: Country ⇸ Bool
  deny_cloud     : Bool
  _cidrlist      : [CIDR_Str]?   -- memoised; cleared on allow_ip
  _cloud_cache   : IP_Str ⇸ {result: Bool, expires: Nat}?
──────────────────────────────────────────────────────────────────

─────────────── New ──────────────────────────────────────────────
  class  : ClassName ∪ ACLState
  params : ACLState?
  ─────────────────────────────────────────────────────────────────
  -- strip_private: removes keys whose names begin with '_'
  blessed(class) ⟹
    result! = bless( deepcopy(class) ∪ strip_private(params),
                     ref(class) )                    -- clone
  ¬blessed(class) ⟹
    result! = bless( strip_private(configure(class, params)),
                     class )
──────────────────────────────────────────────────────────────────

allow_ip

─────────────── AllowIP ──────────────────────────────────────────
  ΔACL
  ip? : IP_Str                 -- must satisfy valid_ip(ip?)
  ─────────────────────────────────────────────────────────────────
  allowed_ips' = allowed_ips₀ // {}   -- initialised on every call
  valid_ip(ip?) ⟹
    allowed_ips' = allowed_ips' ∪ { ip? ↦ 1 }
    _cidrlist'   = ∅          -- cache invalidated
  ¬valid_ip(ip?) ⟹
    allowed_ips' = allowed_ips' -- only initialisation, no entry
    _cidrlist'   = _cidrlist
  deny_countries' = deny_countries
  allow_countries' = allow_countries
  deny_cloud'     = deny_cloud
──────────────────────────────────────────────────────────────────

deny_country

─────────────── DenyCountry ─────────────────────────────────────
  ΔACL
  country? : ISO_Code ∪ {'*'} ∪ seq ISO_Code
  ─────────────────────────────────────────────────────────────────
  country? ∈ seq ISO_Code ⟹
    deny_countries' = deny_countries ∪
                      { lc(c) ↦ 1 | c ∈ country? }
  country? ¬in; seq ISO_Code ⟹
    deny_countries' = deny_countries ∪ { lc(country?) ↦ 1 }
  allow_countries' = allow_countries
  allowed_ips'     = allowed_ips
  deny_cloud'      = deny_cloud
──────────────────────────────────────────────────────────────────

allow_country

─────────────── AllowCountry ────────────────────────────────────
  ΔACL
  country? : ISO_Code ∪ seq ISO_Code
  ─────────────────────────────────────────────────────────────────
  country? ∈ seq ISO_Code ⟹
    allow_countries' = allow_countries ∪
                       { lc(c) ↦ 1 | c ∈ country? }
  country? ¬in; seq ISO_Code ⟹
    allow_countries' = allow_countries ∪ { lc(country?) ↦ 1 }
  deny_countries' = deny_countries
  allowed_ips'    = allowed_ips
  deny_cloud'     = deny_cloud
──────────────────────────────────────────────────────────────────

deny_cloud

─────────────── DenyCloud ───────────────────────────────────────
  ΔACL
  ─────────────────────────────────────────────────────────────────
  deny_cloud'     = 1
  allowed_ips'    = allowed_ips
  deny_countries' = deny_countries
  allow_countries'= allow_countries
  _cidrlist'      = _cidrlist
──────────────────────────────────────────────────────────────────

deny_all_countries

─────────────── DenyAllCountries ────────────────────────────────
  ΔACL
  ─────────────────────────────────────────────────────────────────
  deny_countries' = deny_countries ∪ { '*' ↦ 1 }
  allow_countries' = allow_countries
  allowed_ips'    = allowed_ips
  deny_cloud'     = deny_cloud
──────────────────────────────────────────────────────────────────

all_denied

──────────────────────── AllDenied ──────────────────────────────
  ΞACL                          -- state unchanged (modulo cache)
  addr    : IPv4 ∪ IPv6         -- REMOTE_ADDR or DEFAULT_ADDR
  lingua? : Lingua              -- country resolver (optional)
  result! : {0, 1}              -- 0 = allow, 1 = deny
  ─────────────────────────────────────────────────────────────────
  no_restrictions(self) ⟹ result! = 0

  ¬valid_ip(addr) ⟹ result! = 1

  deny_cloud = 1 ∧ is_cloud(addr) ⟹ result! = 1
  deny_cloud = 1 ∧ ¬is_cloud(addr)
    ∧ allowed_ips = ∅ ∧ deny_countries = ∅ ⟹ result! = 0
    -- allow_countries is intentionally absent: it never changes the result
    -- without deny_countries('*'), so it is not a meaningful restriction.

  addr ∈ dom(allowed_ips) ⟹ result! = 0
  cidr_match(addr, allowed_ips) ⟹ result! = 0

  deny_countries ≠ ∅ ∧ lingua? = ∅ ⟹ result! = 1
    -- allow_countries alone is vacuous; only deny_countries triggers the check.
  lingua?.country() = undef ⟹ result! = 1

  deny_countries('*') = 1
    ∧ allow_countries(lc(lingua?.country())) = 1 ⟹ result! = 0
  deny_countries('*') = 1
    ∧ allow_countries(lc(lingua?.country())) ≠ 1 ⟹ result! = 1

  deny_countries('*') ≠ 1
    ∧ deny_countries(lc(lingua?.country())) = 1 ⟹ result! = 1
  deny_countries('*') ≠ 1
    ∧ deny_countries(lc(lingua?.country())) ≠ 1 ⟹ result! = 0
──────────────────────────────────────────────────────────────────

LICENSE AND COPYRIGHT

Usage is subject to the GPL2 licence terms. If you use it, please let me know.

To install CGI::ACL, copy and paste the appropriate command in to your terminal.

cpanm

cpanm CGI::ACL

CPAN shell

perl -MCPAN -e shell
install CGI::ACL

For more information on module installation, please visit the detailed CPAN module installation guide.

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NAME

VERSION

SYNOPSIS

Block all cloud-hosted visitors

Allow only specific IP addresses or CIDR ranges

Block visitors from specific countries

Allow only specific countries (allowlist)

Production-grade: IP allowlist + country allowlist + cloud block

Sharing a base ACL across routes with cloning

COMMON PITFALLS

allow_country alone has no effect

deny_cloud overrides allow_ip

Localhost is not automatically allowed

Forgetting the lingua argument

VPN and proxy users bypass IP and country checks

Country codes are case-insensitive but stored lowercase

The DNS result cache is not shared between CGI requests

SUBROUTINES/METHODS

new

EXAMPLE

API SPECIFICATION

Input

Output

MESSAGES

allow_ip

EXAMPLE

ARGUMENTS

RETURNS

SIDE EFFECTS

API SPECIFICATION

Input

Output

MESSAGES

deny_country

EXAMPLE

ARGUMENTS

RETURNS

SIDE EFFECTS

NOTES

API SPECIFICATION

Input

Output

MESSAGES

allow_country

EXAMPLE

ARGUMENTS

RETURNS

SIDE EFFECTS

NOTES

API SPECIFICATION

Input

Output

MESSAGES

deny_cloud

EXAMPLE

ARGUMENTS

RETURNS

SIDE EFFECTS

NOTES

API SPECIFICATION

Input

Output

MESSAGES

deny_all_countries

EXAMPLE

ARGUMENTS

RETURNS

SIDE EFFECTS

NOTES

API SPECIFICATION

Input

Output

MESSAGES

all_denied

EXAMPLE

ARGUMENTS

RETURNS

SIDE EFFECTS

API SPECIFICATION

Input