Opened 3 years ago

Closed 3 years ago

#15706 closed enhancement (fixed)

bind9 9.16.22 (Security Update)

Reported by: Douglas R. Reno Owned by: Douglas R. Reno
Priority: elevated Milestone: 11.1
Component: BOOK Version: git
Severity: normal Keywords:


New point version

Contains a fix for a security vulnerability that can impact resolver performance by sending repeated broken requests

Change History (4)

comment:1 by Douglas R. Reno, 3 years ago

Owner: changed from blfs-book to Douglas R. Reno
Status: newassigned

comment:2 by Douglas R. Reno, 3 years ago

CVE: CVE-2021-25219

Document version: 2.0
Posting date: 27 October 2021
Program impacted: BIND
Versions affected: 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
Severity: Medium
Exploitable: Remotely


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.

The purpose of a resolver's lame cache is to ensure that if an 
authoritative server responds to a resolver's query in a specific broken 
way, subsequent client queries for the same <QNAME, QTYPE> tuple do not 
trigger further queries to the same server for a configurable amount of 
time. The lame cache is enabled by setting the lame-ttl option in 
named.conf to a value greater than 0. That option is set to lame-ttl 
600; in the default configuration, which means the lame cache is enabled 
by default.


Authoritative-only BIND 9 servers are NOT vulnerable to this flaw.

A successful attack exploiting this flaw causes a named resolver to 
spend most of its CPU time on managing and checking the lame cache. This 
results in client queries being responded to with large delays, and 
increased likelihood of DNS timeouts on client hosts.

CVSS Score: 4.9


For more information on the Common Vulnerability Scoring System and to 
obtain your specific environmental score, please visit:


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.

Active exploits:

We are not aware of any active exploits.


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

BIND Supported Preview Edition is a special feature preview branch of 
BIND provided to eligible ISC support customers.

     BIND 9.11.36-S1
     BIND 9.16.22-S1

Acknowledgments: ISC would like to thank Kishore Kumar Kothapalli of 
Infoblox for bringing this vulnerability to our attention.

Document revision history:

1.0 Advance notification to customers, 20 October 2021
1.1 Revised Versions Affected (now includes all older versions of BIND 
Supported Preview Edition), 26 October 2021
2.0 Public disclosure, 27 October 2021

Related documents:

See our BIND 9 Security Vulnerability Matrix for a complete listing of 
security vulnerabilities and versions affected.

Do you still have questions? Questions regarding this advisory should go 
to security-officer at To report a new issue, please encrypt your 
message using security-officer at's PGP key which can be found 
here: If you are unable to use encrypted 
email, you may also report new issues at:


ISC patches only currently supported versions. When possible we indicate 
EOL versions affected. (For current information on which versions are 
actively supported, please see

ISC Security Vulnerability Disclosure Policy:

Details of our current security advisory policy and practice can be 
found in the ISC Software Defect and Security Vulnerability Disclosure 
Policy at

The Knowledgebase article is the 
complete and official security advisory document.

comment:3 by Douglas R. Reno, 3 years ago

Feature Changes

    The use of native PKCS#11 for Public-Key Cryptography in BIND 9 has been deprecated in favor of OpenSSL engine_pkcs11 from the OpenSC project. The --with-native-pkcs11 configuration option will be removed from the next major BIND 9 release. The option to use the engine_pkcs11 OpenSSL engine is already available in BIND 9; please see the ARM section on PKCS#11 for details. [GL #2691]

    named and named-checkconf now issue a warning when there is a single configured port in the query-source, transfer-source, notify-source, and parental-source, and/or in their respective IPv6 counterparts. [GL #2888]

    named and named-checkconf now return an error when the single configured port in the query-source, transfer-source, notify-source, parental-source, and/or their respective IPv6 counterparts clashes with the global listening port. This configuration is no longer supported as of BIND 9.16.0 but no error was reported, although sending UDP messages (such as notifies) would fail. [GL #2888]

    The masterfile-format format map has been marked as deprecated and will be removed in a future release. [GL #2882]

    The statically compiled DLZ drivers have been marked as deprecated in favor of dynamically loaded DLZ modules and will be removed in a future major release. [GL #2814]

Bug Fixes

    When new IP addresses were added to the system during named startup, named failed to listen on TCP for the newly added interfaces. [GL #2852]

    Reloading a catalog zone that referenced a missing/deleted zone caused a crash. This has been fixed. [GL #2308]

comment:4 by Douglas R. Reno, 3 years ago

Resolution: fixed
Status: assignedclosed

Fixed at 45befbbe63c7b48b0bda78ad347056ec8f0d619e

Security Advisory also published.

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