/ 
Net-DNS-1.37_01
/ check_zone
Security Advisories (3)
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.

CVE-2026-81928 (2026-09-01)

Net::DNS versions before 1.57 for Perl allow memory exhaustion via unbounded recursion in sig_data when re-encoding a message with a misplaced TSIG record. sig_data signs a message by re-encoding it, and removes TSIG records only from the additional section. A TSIG decoded into the answer or authority section survives that step and is signed again, so encoding re-enters sig_data with no termination condition. Decoding does not reject such a message: a TSIG that is not the last record on the wire raises "misplaced or corrupt TSIG", but the error is caught, reported as a warning, and the record is left in the packet. RFC 8945 section 5.2 requires the message to be dropped. The recursion is reached only when the decoded TSIG carries an empty MAC, since a MAC recovered from the wire short-circuits the signing step. It is reached only from code that re-encodes a message it decoded, such as a forwarder or a proxy. A decoded message that is never re-encoded is unaffected. Message direction does not matter: a query reaches the same path as a response. Each cycle re-encodes the whole message, so fewer than 100 bytes on the wire exhaust available memory and terminate the process.

NAME

check_zone - Check a DNS zone for errors

SYNOPSIS

check_zone [ -r ][ -v ] domain [ class ]

DESCRIPTION

Checks a DNS zone for errors. Current checks are:

  • Checks the domain's SOA from each of the domain's name servers. The SOA serial numbers should match. This program's output cannot be trusted if they do not.

  • Tries to perform an AXFR from each of the domain's name servers. This test helps to detect whether the name server is blocking AXFR.

  • Checks that all A records have corresponding PTR records. For each A record its PTR's name is match checked.

  • Checks that all PTR records match an A record (sometimes they match a CNAME). Check the PTR's name against the A record.

  • Checks that hosts listed in NS, MX, and CNAME records have A records. Checks for NS and CNAME records not pointing to another CNAME (i.e., they must directly resolve to an A record). That test may be somewhat controversial because, in many cases, a MX to a CNAME or a CNAME to another CNAME will resolve; however, in DNS circles it isn't a recommended practise.

  • Check each record processed for being with the class requested. This is an internal integrity check.

OPTIONS

-r

Perform a recursive check on subdomains.

-v

Verbose.

-a alternate_domain

Treat <alternate_domain> as equal to <domain>. This is useful when supporting a change of domain names (eg from myolddomain.example.net to mynewdomain.example.net) where the PTR records can point to only one of the two supported domains (which are otherwise identical).

-e exception_file

Ignore exceptions in file <exception_file>. File format can be space-separated domain pairs, one pair per line, or it can be straight output from this program itself (for simple cut-and-paste functionality). This allows for skipping entries that are odd or unusual, but not causing problems. Note: this only works with A - PTR checks.

AUTHORS

Originally developed by Michael Fuhr (mfuhr@dimensional.com) and hacked--with furor--by Dennis Glatting (dennis.glatting@software-munitions.com).

"-a" and "-e" options added by Paul Archer

SEE ALSO

perl(1), axfr, check_soa, mx, perldig, Net::DNS

BUGS

A query for an A RR against a name that is a CNAME may not follow the CNAME to an A RR.

There isn't a mechanism to insure records are returned from an authoritative source.

There appears to be a bug in the resolver AXFR routine where, if one server cannot be contacted, the routine doesn't try another in its list.