Headline
CVE-2023-2911: CVE-2023-2911
If the recursive-clients
quota is reached on a BIND 9 resolver configured with both stale-answer-enable yes;
and stale-answer-client-timeout 0;
, a sequence of serve-stale-related lookups could cause named
to loop and terminate unexpectedly due to a stack overflow.
This issue affects BIND 9 versions 9.16.33 through 9.16.41, 9.18.7 through 9.18.15, 9.16.33-S1 through 9.16.41-S1, and 9.18.11-S1 through 9.18.15-S1.
CVE-2023-2911: Exceeding the recursive-clients quota may cause named to terminate unexpectedly when stale-answer-client-timeout is set to 0
- Updated on 21 Jun 2023
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CVE: CVE-2023-2911
Document version: 2.0
Posting date: 21 June 2023
Program impacted: BIND 9
Versions affected:
BIND
- 9.16.33 -> 9.16.41
- 9.18.7 -> 9.18.15
BIND Supported Preview Edition
- 9.16.33-S1 -> 9.16.41-S1
- 9.18.11-S1 -> 9.18.15-S1
(BIND 9.11-S versions that support the stale-answer-client-timeout option are not vulnerable.)
Severity: High
Exploitable: Remotely
Description:
If the recursive-clients quota is reached on a BIND 9 resolver configured with both stale-answer-enable yes; and stale-answer-client-timeout 0;, a sequence of serve-stale-related lookups could cause named to loop and terminate unexpectedly due to a stack overflow.
Impact:
By sending specific queries to the resolver, an attacker can cause named to terminate unexpectedly.
CVSS Score: 7.5
CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
For more information on the Common Vulnerability Scoring System and to obtain your specific environmental score please visit: https://nvd.nist.gov/vuln-metrics/cvss/v3-calculator?vector=AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H&version=3.1.
Workarounds:
Setting stale-answer-client-timeout to off or to a non-zero value prevents the issue.
Users of versions 9.18.10, 9.16.36, 9.16.36-S1 or older who are unable to upgrade should set stale-answer-client-timeout to off; using a non-zero value with these older versions leaves named vulnerable to CVE-2022-3924.
Although it is possible to set the recursive-clients limit to a high number to reduce the likelihood of this scenario, this is not recommended; the limit on recursive-clients is important for preventing exhaustion of server resources. The limit cannot be disabled entirely.
Active exploits:
This flaw was discovered in internal testing. We are not aware of any active exploits.
Solution:
Upgrade to the patched release most closely related to your current version of BIND 9:
- 9.16.42
- 9.18.16
BIND Supported Preview Edition is a special feature preview branch of BIND provided to eligible ISC support customers.
- 9.16.42-S1
- 9.18.16-S1
Document revision history:
- 1.0 Early Notification, 14 June 2023
- 2.0 Public disclosure, 21 June 2023
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 be mailed to [email protected]. To report a new issue, please encrypt your message using [email protected]’s PGP key, which can be found here: https://www.isc.org/pgpkey/. If you are unable to use encrypted email you may also report new issues at: https://www.isc.org/reportbug/.
Note:
ISC patches only currently supported versions. When possible we indicate EOL versions affected. For current information on which versions are actively supported, please see https://www.isc.org/download/.
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 https://kb.isc.org/docs/aa-00861.
The Knowledgebase article https://kb.isc.org/docs/cve-2023-2911 is the complete and official security advisory document.
Legal Disclaimer:
Internet Systems Consortium (ISC) is providing this notice on an “AS IS” basis. No warranty or guarantee of any kind is expressed in this notice and none should be implied. ISC expressly excludes and disclaims any warranties regarding this notice or materials referred to in this notice, including, without limitation, any implied warranty of merchantability, fitness for a particular purpose, absence of hidden defects, or of non-infringement. Your use or reliance on this notice or materials referred to in this notice is at your own risk. ISC may change this notice at any time. A stand-alone copy or paraphrase of the text of this document that omits the document URL is an uncontrolled copy. Uncontrolled copies may lack important information, be out of date, or contain factual errors.
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This issue can affect BIND 9 resolvers with `stale-answer-enable yes;` that also make use of the option `stale-answer-client-timeout`, configured with a value greater than zero. If the resolver receives many queries that require recursion, there will be a corresponding increase in the number of clients that are waiting for recursion to complete. If there are sufficient clients already waiting when a new client query is received so that it is necessary to SERVFAIL the longest waiting client (see BIND 9 ARM `recursive-clients` limit and soft quota), then it is possible for a race to occur between providing a stale answer to this older client and sending an early timeout SERVFAIL, which may cause an assertion failure. This issue affects BIND 9 versions 9.16.12 through 9.16.36, 9.18.0 through 9.18.10, 9.19.0 through 9.19.8, and 9.16.12-S1 through 9.16.36-S1.
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