CVE-2021-25218

Public Exploit
A too-strict assertion check could be triggered when responses in BIND 9.16.19 and 9.17.16 require UDP fragmentation if RRL is in use

Description

In BIND 9.16.19, 9.17.16. Also, version 9.16.19-S1 of BIND Supported Preview Edition When a vulnerable version of named receives a query under the circumstances described above, the named process will terminate due to a failed assertion check. The vulnerability affects only BIND 9 releases 9.16.19, 9.17.16, and release 9.16.19-S1 of the BIND Supported Preview Edition.

Remediation

Solution:

  • Upgrade to the patched release most closely related to your current version of BIND: BIND 9.16.20 BIND 9.17.17 BIND Supported Preview Edition is a special feature preview branch of BIND provided to eligible ISC support customers. BIND 9.16.20-S1

Workaround:

  • Disabling RRL in all views, including the built-in CHAOS class view "_bind", prevents the faulty assertion from being reached. This can be done by removing all existing rate-limit statements from named.conf, and defining a replacement for the default CHAOS view: view override_bind chaos { recursion no; notify no; allow-new-zones no; max-cache-size 2M; zone "version.bind" chaos { type primary; database "_builtin version"; }; zone "hostname.bind" chaos { type primary; database "_builtin hostname"; }; zone "authors.bind" chaos { type primary; database "_builtin authors"; }; zone "id.server" chaos { type primary; database "_builtin id"; }; };

Category

7.5
CVSS
Severity: High
CVSS 3.1 •
CVSS 2.0 •
EPSS 0.40%
Vendor Advisory fedoraproject.org Vendor Advisory isc.org
Affected: ISC BIND9
Published at:
Updated at:

References

Link Tags
https://kb.isc.org/v1/docs/cve-2021-25218 exploit vendor advisory
http://www.openwall.com/lists/oss-security/2021/08/18/3 mailing list third party advisory patch
http://www.openwall.com/lists/oss-security/2021/08/20/2 mailing list third party advisory patch
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ZPJCLGSR4BTGFLBLGIE5TEQP2SNJKGVL/ vendor advisory
https://security.netapp.com/advisory/ntap-20210909-0002/ third party advisory

Frequently Asked Questions

What is the severity of CVE-2021-25218?
CVE-2021-25218 has been scored as a high severity vulnerability.
How to fix CVE-2021-25218?
To fix CVE-2021-25218: Upgrade to the patched release most closely related to your current version of BIND: BIND 9.16.20 BIND 9.17.17 BIND Supported Preview Edition is a special feature preview branch of BIND provided to eligible ISC support customers. BIND 9.16.20-S1
Is CVE-2021-25218 being actively exploited in the wild?
It is possible that CVE-2021-25218 is being exploited or will be exploited in a near future based on public information. According to its EPSS score, there is a ~0% probability that this vulnerability will be exploited by malicious actors in the next 30 days.
What software or system is affected by CVE-2021-25218?
CVE-2021-25218 affects ISC BIND9.
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