/ 
Net-DNS-1.55_01
/ Net::DNS::FAQ
Security Advisories (1)
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

Net::DNS::FAQ - Frequently Asked Net::DNS Questions

SYNOPSIS

perldoc Net::DNS::FAQ

DESCRIPTION

This document serves to answer the most frequently asked questions on both the Net::DNS Mailing List and those sent to the author.

The latest version of this FAQ can be found at http://www.net-dns.org/docs/FAQ.html

GENERAL

What is Net::DNS?

Net::DNS is a perl implementation of a DNS resolver.

INSTALLATION

Where can I find Test::More?

Test::More is part of the Test-Simple package, by Michael G Schwern. You should be able to find the distribution at http://search.cpan.org/dist/Test-Simple/

USAGE

Why does $resolver->query() return undef when the answer section is empty?

The short answer is, do not use query(). $resolver->send() will always return the response packet, as long as a response was received.

The longer answer is that query() is modeled after the res_query() function from the libresolv C library, which has similar behavior.

VERSION

$Id: FAQ.pod 1709 2018-09-07 08:03:09Z willem $