CVE-2019-6475: A flaw in mirror zone validity checking can allow zone data to be spoofed

CVE: CVE-2019-6475

Document version: 2.0

Posting date: 16 October 2019

Program impacted: BIND

Versions affected: BIND 9.14.0 -> 9.14.6 Also releases 9.15.0 -> 9.15.4 of the BIND 9.15 development branch.

Severity: Medium

Exploitable: Remotely

Description:

Mirror zones are a BIND feature allowing recursive servers to pre-cache zone data provided by other servers. A mirror zone is similar to a zone of type secondary, except that its data is subject to DNSSEC validation before being used in answers, as if it had been looked up via traditional recursion, and when mirror zone data cannot be validated, BIND falls back to using traditional recursion instead of the mirror zone. However, an error in the validity checks for the incoming zone data can allow an on-path attacker to replace zone data that was validated with a configured trust anchor with forged data of the attacker's choosing.

The mirror zone feature is most often used to serve a local copy of the root zone. If an attacker was able to insert themselves into the network path between a recursive server using a mirror zone and a root name server, this vulnerability could then be used to cause the recursive server to accept a copy of falsified root zone data.

Impact:

An on-path attacker who manages to successfully exploit this vulnerability can replace the mirrored zone (usually the root) with data of their own choosing, effectively bypassing DNSSEC protection.

CVSS Score: 5.9

CVSS Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N

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:H/PR:N/UI:N/S:U/C:N/I:H/A:N.

Workarounds:

The vulnerability can be avoided by disabling the mirror zone feature.

Active exploits:

None known.

Solution:

Upgrade to the patched release most closely related to your current version of BIND:

• BIND 9.14.7
• BIND 9.15.5

Document revision history:

1.0 Early Notification, 09 October 2019
2.0 Public Disclosure, 16 October 2019

Related documents:

See our BIND 9 Security Vulnerability Matrix 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 https://www.isc.org/downloads/.)

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.

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

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