An heap-based buffer overflow was discovered in dnsmasq when DNSSEC is enabled and before it validates the received DNS entries. A remote attacker, who can create valid DNS replies, could use this flaw to cause an overflow in a heap-allocated memory. This flaw is caused by the lack of length checks in rfc1035.c:extract_name(), which could be abused to make the code execute memcpy() with a negative size in get_rdata() and cause a crash in dnsmasq.
To trigger the flaw, dnsmasq has to be compiled with HAVE_DNSSEC flag and DNSSEC has to be enabled (e.g. with --dnssec option). Moreover, the attacker shall either control a DNS server used in the domain name resolution process or be able to inject packets on the network in such a way to trick dnsmasq into accepting them (e.g. guessing the ID, random port used, etc.). To be involved in the domain name resolution process, an attacker could trick a victim which uses dnsmasq into accessing some resources on a controlled domain, e.g. trick the user to visit a website or open an email. If the dnsmasq service is an Open Resolver (it accepts requests from the whole Internet) or the attacker is on the internal network covered by dnsmasq, the attack can be performed at will by the attacker, without requiring any other user interaction.
Acknowledgments: Name: Moshe Kol (JSOF), Shlomi Oberman (JSOF)
Statement: This issue does not affect the versions of dnsmasq as shipped with Red Hat Enterprise Linux 5, 6, and 7 as they are not compiled with DNSSEC support.
External References: https://www.jsof-tech.com/disclosures/dnspooq/
Mitigation: The only known way to mitigate this flaw is to disable DNSSEC altogether, by removing the `--dnssec` command line option or the `dnssec` option from dnsmasq configuration file.
Created dnsmasq tracking bugs for this issue: Affects: fedora-all [bug 1917783]
This issue has been addressed in the following products: Red Hat Enterprise Linux 8.1 Extended Update Support Via RHSA-2021:0152 https://access.redhat.com/errata/RHSA-2021:0152
This issue has been addressed in the following products: Red Hat Enterprise Linux 8 Via RHSA-2021:0150 https://access.redhat.com/errata/RHSA-2021:0150
Upstream patch: http://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=commit;h=4e96a4be685c9e4445f6ee79ad0b36b9119b502a
This issue has been addressed in the following products: Red Hat Enterprise Linux 8.2 Extended Update Support Via RHSA-2021:0151 https://access.redhat.com/errata/RHSA-2021:0151
This bug is now closed. Further updates for individual products will be reflected on the CVE page(s): https://access.redhat.com/security/cve/cve-2020-25683