ALAS2-2021-1587


Amazon Linux 2 Security Advisory: ALAS-2021-1587
Advisory Release Date: 2021-01-25 23:09 Pacific
Advisory Updated Date: 2021-01-26 18:43 Pacific
Severity: Medium

Issue Overview:

A flaw was found in dnsmasq. When getting a reply from a forwarded query, dnsmasq checks in the forward.c:reply_query() if the reply destination address/port is used by the pending forwarded queries. However, it does not use the address/port to retrieve the exact forwarded query, substantially reducing the number of attempts an attacker on the network would have to perform to forge a reply and get it accepted by dnsmasq. This issue contrasts with RFC5452, which specifies a query's attributes that all must be used to match a reply. This flaw allows an attacker to perform a DNS Cache Poisoning attack. If chained with CVE-2020-25685 or CVE-2020-25686, the attack complexity of a successful attack is reduced. The highest threat from this vulnerability is to data integrity. (CVE-2020-25684)

A flaw was found in dnsmasq. When getting a reply from a forwarded query, dnsmasq checks in forward.c:reply_query(), which is the forwarded query that matches the reply, by only using a weak hash of the query name. Due to the weak hash (CRC32 when dnsmasq is compiled without DNSSEC, SHA-1 when it is) this flaw allows an off-path attacker to find several different domains all having the same hash, substantially reducing the number of attempts they would have to perform to forge a reply and get it accepted by dnsmasq. This is in contrast with RFC5452, which specifies that the query name is one of the attributes of a query that must be used to match a reply. This flaw could be abused to perform a DNS Cache Poisoning attack. If chained with CVE-2020-25684 the attack complexity of a successful attack is reduced. The highest threat from this vulnerability is to data integrity. (CVE-2020-25685)

A flaw was found in dnsmasq. When receiving a query, dnsmasq does not check for an existing pending request for the same name and forwards a new request. By default, a maximum of 150 pending queries can be sent to upstream servers, so there can be at most 150 queries for the same name. This flaw allows an off-path attacker on the network to substantially reduce the number of attempts that it would have to perform to forge a reply and have it accepted by dnsmasq. This issue is mentioned in the "Birthday Attacks" section of RFC5452. If chained with CVE-2020-25684, the attack complexity of a successful attack is reduced. The highest threat from this vulnerability is to data integrity. (CVE-2020-25686)


Affected Packages:

dnsmasq


Issue Correction:
Run yum update dnsmasq to update your system.

New Packages:
aarch64:
    dnsmasq-2.76-16.amzn2.1.1.aarch64
    dnsmasq-utils-2.76-16.amzn2.1.1.aarch64
    dnsmasq-debuginfo-2.76-16.amzn2.1.1.aarch64

i686:
    dnsmasq-2.76-16.amzn2.1.1.i686
    dnsmasq-utils-2.76-16.amzn2.1.1.i686
    dnsmasq-debuginfo-2.76-16.amzn2.1.1.i686

src:
    dnsmasq-2.76-16.amzn2.1.1.src

x86_64:
    dnsmasq-2.76-16.amzn2.1.1.x86_64
    dnsmasq-utils-2.76-16.amzn2.1.1.x86_64
    dnsmasq-debuginfo-2.76-16.amzn2.1.1.x86_64