CVE-2021-25220: DNS forwarders - cache poisoning vulnerability
A cache poisoning vulnerability was found in BIND when using forwarders. Bogus NS records supplied by the forwarders may be cached and used by name if it needs to recurse for any reason. This issue causes it to obtain and pass on potentially incorrect answers. This flaw allows a remote high privileged attacker to manipulate cache results with incorrect records, leading to queries made to the wrong servers, possibly resulting in false information received on the client's end.
Other sources
BIND 9.11.0 -> 9.11.36 9.12.0 -> 9.16.26 9.17.0 -> 9.18.0 BIND Supported Preview Editions: 9.11.4-S1 -> 9.11.36-S1 9.16.8-S1 -> 9.16.26-S1 Versions of BIND 9 earlier than those shown - back to 9.1.0, including Supported Preview Editions - are also believed to be affected but have not been tested as they are EOL. The cache could become poisoned with incorrect records leading to queries being made to the wrong servers, which might also result in false information being returned to clients.
When using forwarders, bogus NS records supplied by, or via, those forwarders may be cached and used by named if it needs to recurse for any reason, causing it to obtain and pass on potentially incorrect answers.
Some examples of configurations that will be vulnerable are:
Resolvers using per zone or global forwarding with forward first (forward first is the default). Resolvers not using global forwarding, but with per-zone forwarding with either forward first (the default) or forward only. Resolvers configured with global forwarding along with zone statements that disable forwarding for part of the DNS namespace.
Authoritative-only BIND 9 servers are not vulnerable to this flaw.
— Red Hat
Affected Software
Remediation
Information
Information
Event History
Parent advisories
This vulnerability appears in the following advisories.
Frequently Asked Questions
What is the severity of CVE-2021-25220?
CVE-2021-25220 is rated as high severity due to the potential for unauthorized access and exploitation of vulnerable BIND versions.
How do I fix CVE-2021-25220?
To fix CVE-2021-25220, upgrade to the latest patched version of BIND, which are 9.11.37, 9.16.27, or 9.18.1, depending on your distribution.
Which versions of BIND are affected by CVE-2021-25220?
CVE-2021-25220 affects BIND versions from 9.11.0 to 9.11.36, 9.12.0 to 9.16.26, and 9.17.0 to 9.18.0.
What are the recommended actions for users running vulnerable versions of BIND due to CVE-2021-25220?
Users running vulnerable versions should immediately apply updates or install the recommended patches to mitigate the risk associated with CVE-2021-25220.
Is CVE-2021-25220 being actively exploited in the wild?
While there are indicators of this vulnerability being targeted, it is advisable for users to implement updates to minimize security risks.