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Two Vulnerabilities Patched in BIND DNS Software

Updates announced on Friday by the Internet Systems Consortium (ISC) for BIND, the most widely used Domain Name System (DNS) software, patch a couple of vulnerabilities.

While attackers may be able to exploit both of the flaws remotely for denial-of-service (DoS) attacks, the security holes have been assigned only a “medium” severity rating.

One of the vulnerabilities, tracked as CVE-2018-5737, can allow a remote attacker to cause operational problems, including degradation of the service or a DoS condition.

“A problem with the implementation of the new serve-stale feature in BIND 9.12 can lead to an assertion failure in rbtdb.c, even when stale-answer-enable is off,” ISC explained in an advisory. “Additionally, problematic interaction between the serve-stale feature and NSEC aggressive negative caching can in some cases cause undesirable behavior from named, such as a recursion loop or excessive logging.”

The vulnerability impacts BIND 9.12.0 and 9.12.1 if the server is configured to allow recursion to clients and the max-stale-ttl parameter has a value other than zero. The issue has been patched in BIND 9.12.1-P2, but workarounds are also available.

The second flaw, CVE-2018-5736, is also remotely exploitable, but only if the attacker can trigger a zone transfer.

“An error in zone database reference counting can lead to an assertion failure if a server which is running an affected version of BIND attempts several transfers of a slave zone in quick succession,” ISC wrote. “This defect could be deliberately exercised by an attacker who is permitted to cause a vulnerable server to initiate zone transfers (for example: by sending valid NOTIFY messages), causing the named process to exit after failing the assertion test.”

This vulnerability impacts BIND 9.12.0 and 9.12.1, and it has been patched in version 9.12.1-P1. However, users need to update to version 9.12.1-P2 as version 9.12.1-P1 was recalled before the public announcement due to a defect.

ISC support customers, including OEMs that re-package the organization’s open source code into commercial products, were notified about these vulnerabilities on May 9.

The latest version of BIND also includes a security improvement related to update-policy rules. ISC also noted that “named will now log a warning if the old root DNSSEC key is explicitly configured and has not been updated.”

This is the third round of security updates released for BIND this year. The first was released in mid-January and the second in late February. The February update impacted BIND Supported Preview Edition, but not any publicly released versions.

Related: Authentication Bypass Flaw Patched in BIND, Knot DNS

Related: Critical Flaw Patched in BIND Installer for Windows

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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.