/ 
Net-DNS-0.63
/ check_soa
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

check_soa - Check nameservers for a domain

SYNOPSIS

check_soa [-d] [-t] [-v] domain [server ...]

DESCRIPTION

check_soa builds a list of nameservers for the zone which contains the specified domain name. The program queries each nameserver for the relevant SOA record and reports the zone serial number.

domain

Fully qualified domain name to be tested. Domains within ip6.arpa or in-addr.arpa namespaces may be specified using the appropriate IP address or prefix.

server

Optional name or list of IP addresses of specific nameserver to be tested. Addresses are used in the sequence they appear in the argument list.

Error reports are generated for nameservers which reply with non-authoritative, outdated or incorrect information.

SOA query packets are sent to the nameservers as rapidly as the underlying hardware will allow. The program waits for a response only when it is needed for analysis. Execution time is determined by the slowest nameserver.

The perldoc(1) documentation page is displayed if the domain argument is omitted.

This program is based on the check_soa idea described by Albitz and Liu.

OPTIONS

-d

Turn on resolver diagnostics.

-t

Ignore UDP datagram truncation.

-v

Verbose output including address records for each server.

EXAMPLES

check_soa example.com

Query all nameservers for the specified domain.

check_soa example.com ns.icann.org

Query specific nameserver as above.

check_soa 192.168.99.0

Query nameservers for specified in-addr.arpa subdomain.

check_soa 2001:DB8::8:800:200C:417A

Query nameservers for specified ip6.arpa subdomain.

check_soa 2001:DB8:0:CD30::/60

As above, for IPv6 address prefix of specified length.

BUGS

The timeout code exploits the 4 argument form of select() function. This is not guaranteed to work in non-Unix environments.

COPYRIGHT

(c) 2003-2007 Dick Franks <rwfranks[...]acm.org>

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

SEE ALSO

Paul Albitz, Cricket Liu. DNS and BIND, 5th Edition. O'Reilly & Associates, 2006.

M. Andrews. Negative Caching of DNS Queries. RFC2308, IETF Network Working Group, 1998.

Tom Christiansen, Jon Orwant, Larry Wall. Programming Perl, 3rd Edition. O'Reilly & Associates, 2000.

R. Elz, R. Bush. Clarifications to the DNS Specification. RFC2181, IETF Network Working Group, 1997.

P. Mockapetris. Domain Names - Concepts and Facilities. RFC1034, IETF Network Working Group, 1987.