CVE-2021-25219

Lame cache can be abused to severely degrade resolver performance

Description

In BIND 9.3.0 -> 9.11.35, 9.12.0 -> 9.16.21, and versions 9.9.3-S1 -> 9.11.35-S1 and 9.16.8-S1 -> 9.16.21-S1 of BIND Supported Preview Edition, as well as release versions 9.17.0 -> 9.17.18 of the BIND 9.17 development branch, exploitation of broken authoritative servers using a flaw in response processing can cause degradation in BIND resolver performance. The way the lame cache is currently designed makes it possible for its internal data structures to grow almost infinitely, which may cause significant delays in client query processing.

Remediation

Solution:

  • Upgrade to the patched release most closely related to your current version of BIND: BIND 9.11.36, BIND 9.16.22, BIND 9.17.19, or for BIND Supported Preview Edition (a special feature preview branch of BIND provided to eligible ISC support customers): BIND 9.11.36-S1, BIND 9.16.22-S1.

Workaround:

  • Setting "lame-ttl 0;" disables the lame cache and prevents the performance issue. Our research and testing indicate that in the current Internet there is almost no downside to disabling the lame cache.
5.3
CVSS
Severity: Medium
CVSS 3.1 •
CVSS 2.0 •
EPSS 0.52%
Vendor Advisory debian.org Vendor Advisory fedoraproject.org Vendor Advisory fedoraproject.org Vendor Advisory fedoraproject.org Vendor Advisory gentoo.org Vendor Advisory isc.org
Affected: ISC BIND9
Published at:
Updated at:

References

Link Tags
https://kb.isc.org/v1/docs/cve-2021-25219 vendor advisory
https://www.debian.org/security/2021/dsa-4994 third party advisory vendor advisory
https://lists.debian.org/debian-lts-announce/2021/11/msg00001.html third party advisory mailing list
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/YTKC4E3HUOLYN5IA4EBL4VAQSWG2ZVTX/ vendor advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/YGV7SA27CTYLGFJSPUM3V36ZWK7WWDI4/ vendor advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/EF4NAVRV4H3W4GA3LGGZYUKD3HSJBAVW/ vendor advisory
https://www.oracle.com/security-alerts/cpuapr2022.html third party advisory
https://cert-portal.siemens.com/productcert/pdf/ssa-389290.pdf third party advisory patch
https://security.netapp.com/advisory/ntap-20211118-0002/ third party advisory
https://security.gentoo.org/glsa/202210-25 third party advisory vendor advisory

Frequently Asked Questions

What is the severity of CVE-2021-25219?
CVE-2021-25219 has been scored as a medium severity vulnerability.
How to fix CVE-2021-25219?
To fix CVE-2021-25219: Upgrade to the patched release most closely related to your current version of BIND: BIND 9.11.36, BIND 9.16.22, BIND 9.17.19, or for BIND Supported Preview Edition (a special feature preview branch of BIND provided to eligible ISC support customers): BIND 9.11.36-S1, BIND 9.16.22-S1.
Is CVE-2021-25219 being actively exploited in the wild?
As for now, there are no information to confirm that CVE-2021-25219 is being actively exploited. According to its EPSS score, there is a ~1% probability that this vulnerability will be exploited by malicious actors in the next 30 days.
What software or system is affected by CVE-2021-25219?
CVE-2021-25219 affects ISC BIND9.
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