When configured to perform DNSSEC validation, named can crash when encountering a rare set of conditions in the managed trust anchors.
Posting date: 18 Feb 2015
BIND 9.7.0 -> BIND 9.10.1-P1. Also, b1 and rc1 development versions of the upcoming BIND maintenance releases (9.9.7b1 & rc1, 9.10.2b1 & rc1) are affected.
BIND versions 9.9.6, 9.9.6-P1, 9.10.1, and 9.10.1-P1 will terminate consistently with an assertion in zone.c, but previous affected versions may exhibit unpredictable behaviour, including server crashes, due to the use of an improperly initialized variable.
High, but requires specific conditions.
Remotely, under limited circumstances.
BIND servers which are configured to perform DNSSEC validation and which are using managed-keys (which occurs implicitly when using "dnssec-validation auto;" or "dnssec-lookaside auto;") may terminate with an assertion failure when encountering all of the following conditions in a managed trust anchor:
- a key which was previously trusted is now flagged as revoked;
- there are no other trusted keys available;
- there is a standby key, but it is not trusted yet
This situation results in termination of the named process and denial of service to clients, and can occur in two circumstances:
- during an improperly-managed key rollover for one of the managed trust anchors (e.g., during a botched root key rollover), or
- when deliberately triggered by an attacker, under specific and limited circumstances. ISC has demonstrated a proof-of-concept of this attack; however, the complexity of the attack is very high unless the attacker has a specific network relationship to the BIND server which is targeted
Only servers which are performing DNSSEC validation and which are using managed-keys can be affected by this vulnerability.
Recursive validating resolvers are at the greatest risk, but authoritative servers could also be vulnerable if they are performing DNSSEC validation and using managed-keys.
Servers which are affected may terminate with an assertion, causing denial of service to all clients.
CVSS Score: 5.4
CVSS Vector: (AV:N/AC:H/Au:N/C:N/I:N/A:C)
For more information on the Common Vulnerability Scoring System and to obtain your specific environmental score please visit: http://nvd.nist.gov/cvss.cfm?calculator&version=2&vector=(AV:N/AC:H/Au:N/C:N/I:N/A:C)
For a workaround, do not use "auto" for the dnssec-validation or dnssec-lookaside options and do not configure a managed-keys statement. In order to do DNSSEC validation with this workaround one would have to configure an explicit trusted-keys statement with the appropriate keys.
No known active exploits.
Upgrade to the patched release most closely related to your current version of BIND. These can be downloaded from http://www.isc.org/downloads.
- BIND 9.9.6-P2
- BIND 9.10.1-P2
The issue is also fixed in the BIND development releases:
- BIND 9.9.7rc2
- BIND 9.10.2rc2
Acknowledgements: ISC would like to thank Jan-Piet Mens for reporting this issue.
Document Revision History:
1.0 Advance Notification, 11 February 2015
2.0 Updated Workaround section, Public Disclosure, 18 February 2015
See our BIND9 Security Vulnerability Matrix at https://kb.isc.org/article/AA-00913 for a complete listing of Security Vulnerabilities and versions affected.
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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 http://www.isc.org/downloads/).
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This Knowledge Base article https://kb.isc.org/article/AA-01235 is the complete and official security advisory document.
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