/ 
Net-DNS-0.68_07
/ Net::DNS::RR::TSIG
Security Advisories (2)
CVE-2026-64193 (2026-07-20)

Net::DNS versions through 1.55 for Perl allow remote execution injection via EDNS EXTENDED ERROR. Net::DNS::RR::OPT::EXTENDED_ERROR::_decompose parses the EXTRA-TEXT field of an EDNS EXTENDED-ERROR option (RFC 8914) by tokenising the raw bytes and passing the result to Perl's eval. There is some escaping done for $ and @, but not for backticks. This can be exploited for command execution if $pkt->edns->option('EXTENDED-ERROR') is called in array context, for example with a payload of {0:`"<command>"`} in EXTRA-TEXT.

CVE-2026-64194 (2026-07-20)

Net::DNS versions through 1.55 for Perl allow Denial of Service via deep DNS compression pointer chains. Net::DNS::DomainName::decode follows RFC 1035 compression pointers by recursing into itself with no depth limit. It is possible to construct a name which saturates the call stack (at least with larger TCP responses), leading to a potential Denial of Service. The guard `$link < $offset` prevents forward and circular chains, but still allows arbitrarily long backward chains. The per-offset cache (`$cache`) is populated at the start of each call and short-circuits only re-traverses of the same offset - the initial descent through a fresh chain still recurses at full depth. A crafted packet can chain two-byte compression pointers so that each one points two bytes earlier than the previous, producing a chain length of `offset / 2`. For the 14-bit pointer field (max offset 16383) this gives up to ~8191 recursive frames. For a TCP DNS message the limit is the 16-bit length field (~32767 frames). Perl's default C stack handles only a few thousand frames; beyond that the process receives SIGSEGV or similar, which is a denial-of-service for any application parsing untrusted DNS data. The vulnerability is triggered by `Net::DNS::Packet->new(\$wire)` i.e. any point where the library decodes a DNS message from the network.

NAME

Net::DNS::RR::TSIG - DNS TSIG resource record

SYNOPSIS

use Net::DNS;

DESCRIPTION

Class for DNS Transaction Signature (TSIG) resource records.

METHODS

The available methods are those inherited from the base class augmented by the type-specific methods defined in this package.

Use of undocumented package features or direct access to internal data structures is discouraged and could result in program termination or other unpredictable behaviour.

algorithm

$algorithm = $rr->algorithm;

A domain name which specifies the name of the algorithm.

key

$key = $rr->key;

Base64 encoded key.

time_signed

$time_signed = $rr->time_signed;

Signing time as the number of seconds since 1 Jan 1970 00:00:00 UTC. The default signing time is the current time.

fudge

$fudge = $rr->fudge;

"fudge" represents the permitted error in the signing time. The default fudge is 300 seconds.

mac

Returns the message authentication code (MAC) as a string of hex characters. The programmer must call the Net::DNS::Packet data() object method before this will return anything meaningful.

macbin

$macbin = $rr->macbin;

Binary message authentication code (MAC).

original_id

$original_id = $rr->original_id;

The message ID from the header of the original packet.

error

$rcode = $tsig->error;

Returns the RCODE covering TSIG processing. Common values are NOERROR, BADSIG, BADKEY, and BADTIME. See RFC 2845 for details.

other

$other = $rr->other;

This field should be empty unless the error is BADTIME, in which case it will contain the server time as the number of seconds since 1 Jan 1970 00:00:00 UTC.

sign_func

$sign_func = $rr->sign_func;

This sets the signing function to be used for this TSIG record. The default signing function is HMAC-MD5.

sig_data

$sigdata = $tsig->sig_data($packet);

Returns the packet packed according to RFC2845 in a form for signing. This is only needed if you want to supply an external signing function, such as is needed for TSIG-GSS.

TSIG Keys

TSIG keys are symmetric HMAC-MD5 keys generated using the following command:

	$ dnssec-keygen -a HMAC-MD5 -b 512 -n HOST <keyname>

	The key will be stored in the file K<keyname>+157+<keyid>.private

    where
	<keyname> is the DNS name of the key.

	<keyid> is the (generated) numerical identifier used to distinguish this key.

It is recommended that the keyname be the fully qualified domain name of the relevant host.

Configuring BIND Nameserver

The following lines must be added to the /etc/named.conf file:

    key <keyname> {
	algorithm HMAC-MD5;
	secret "<keydata>";
    };

<keyname> is the name of the key chosen when the key was generated.

<keydata> is the string found on the Key: line in the generated key file.

ACKNOWLEDGMENT

Most of the code in the Net::DNS::RR::TSIG module was contributed by Chris Turbeville.

Support for external signing functions was added by Andrew Tridgell.

BUGS

A 32-bit representation of time is used, contrary to RFC2845 which demands 48 bits. This design decision will need to be reviewed before the code stops working on 7 February 2106.

HMAC-MD5.SIG-ALG.REG.INT is the only algorithm currently supported. You can use other algorithms by supplying an appropriate sign_func.

COPYRIGHT

Copyright (c)2002 Michael Fuhr.

Portions Copyright (c)2002-2004 Chris Reinhardt.

Package template (c)2009,2012 O.M.Kolkman and R.W.Franks.

All rights reserved.

This program is free software; you may redistribute it and/or modify it under the same terms as Perl itself.

SEE ALSO

perl, Net::DNS, Net::DNS::RR, RFC2845