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perl-5.45.1
⭐ Starred 2013 / Net::netent
Security Advisories (1)
CVE-2026-15534 (2026-08-09)

Perl versions through 5.45.1 have out-of-bounds heap reads and writes during regular expression matching via an undersized superlinear cache in S_regmatch. The regex engine's superlinear cache holds one bit per subject position for each participating WHILEM node, so the bit count is the subject length plus one times the number of nodes. Nothing checks that product for positive overflow of the signed 32-bit count: a 286331153 byte subject matched against a pattern with 15 participating nodes stores the count as 14, leaving a two byte cache. The cache is then indexed from the real match position and node number, so reads go past the end of the allocation, and on failure CACHEsayNO sets a bit past it. A caller that matches an attacker controlled subject of this size against a pattern of this shape can crash the process or corrupt heap memory.

NAME

Net::netent - by-name interface to Perl's built-in getnet*() functions

SYNOPSIS

use Net::netent qw(:FIELDS);
getnetbyname("loopback") 		or die "bad net";
printf "%s is %08X\n", $n_name, $n_net;

use Net::netent;

$n = getnetbyname("loopback") 		or die "bad net";
{ # there's gotta be a better way, eh?
    @bytes = unpack("C4", pack("N", $n->net));
    shift @bytes while @bytes && $bytes[0] == 0;
}
printf "%s is %08X [%d.%d.%d.%d]\n", $n->name, $n->net, @bytes;

DESCRIPTION

This module's default exports override the core getnetbyname() and getnetbyaddr() functions, replacing them with versions that return "Net::netent" objects. This object has methods that return the similarly named structure field name from the C's netent structure from netdb.h; namely name, aliases, addrtype, and net. The aliases method returns an array reference, the rest scalars.

You may also import all the structure fields directly into your namespace as regular variables using the :FIELDS import tag. (Note that this still overrides your core functions.) Access these fields as variables named with a preceding n_. Thus, $net_obj->name() corresponds to $n_name if you import the fields. Array references are available as regular array variables, so for example @{ $net_obj->aliases() } would be simply @n_aliases.

The getnet() function is a simple front-end that forwards a numeric argument to getnetbyaddr(), and the rest to getnetbyname().

To access this functionality without the core overrides, pass the use an empty import list, and then access function functions with their full qualified names. On the other hand, the built-ins are still available via the CORE:: pseudo-package.

EXAMPLES

The getnet() functions do this in the Perl core:

sv_setiv(sv, (I32)nent->n_net);

The gethost() functions do this in the Perl core:

sv_setpvn(sv, hent->h_addr, len);

That means that the address comes back in binary for the host functions, and as a regular perl integer for the net ones. This seems a bug, but here's how to deal with it:

use strict;
use Socket;
use Net::netent;

@ARGV = ('loopback') unless @ARGV;

my($n, $net);

for $net ( @ARGV ) {

    unless ($n = getnetbyname($net)) {
	warn "$0: no such net: $net\n";
	next;
    }

    printf "\n%s is %s%s\n", 
	    $net, 
	    lc($n->name) eq lc($net) ? "" : "*really* ",
	    $n->name;

    print "\taliases are ", join(", ", @{$n->aliases}), "\n"
		if @{$n->aliases};     

    # this is stupid; first, why is this not in binary?
    # second, why am i going through these convolutions
    # to make it looks right
    {
	my @a = unpack("C4", pack("N", $n->net));
	shift @a while @a && $a[0] == 0;
	printf "\taddr is %s [%d.%d.%d.%d]\n", $n->net, @a;
    }

    if ($n = getnetbyaddr($n->net)) {
	if (lc($n->name) ne lc($net)) {
	    printf "\tThat addr reverses to net %s!\n", $n->name;
	    $net = $n->name;
	    redo;
	} 
    }
}

NOTE

While this class is currently implemented using the Class::Struct module to build a struct-like class, you shouldn't rely upon this.

AUTHOR

Tom Christiansen