Security Experts:

Flaw in BIND Security Feature Allows DoS Attacks

The Internet Systems Consortium (ISC) revealed on Wednesday that the BIND DNS software is affected by a serious vulnerability that can be exploited for denial-of-service (DoS) attacks.

The flaw, discovered by Tony Finch of the University of Cambridge and tracked as CVE-2018-5740, can be exploited remotely and it has been assigned a CVSS score of 7.5, which makes it “high severity.”

However, the vulnerability only impacts servers on which a feature called “deny-answer-aliases” has been enabled. The feature is disabled by default.

The “deny-answer-aliases” feature is designed to help recursive server operators protect users against DNS rebinding attacks. These types of attacks allow a remote hacker to abuse the targeted user’s web browser to directly communicate with devices on the local network and exploit any flaws they might have.

“Accidental or deliberate triggering of this defect will cause an INSIST assertion failure in named, causing the named process to stop execution and resulting in denial of service to clients,” ISC wrote in its advisory.

The security hole impacts BIND versions 9.7.0 through 9.8.8, 9.9.0 through 9.9.13, 9.10.0 through 9.10.8, 9.11.0 through 9.11.4, 9.12.0 through 9.12.2, and 9.13.0 through 9.13.2. A patch is included in versions 9.9.13-P1, 9.10.8-P1, 9.11.4-P1 and 9.12.2-P1. As a workaround, ISC suggests disabling the problematic feature if it has been used.

“Most operators will not need to make any changes unless they are using the ‘deny-answer-aliases’ feature. ‘deny-answer-aliases’ is off by default; only configurations which explicitly enable it can be affected by this defect,” ISC said.

The organization says it’s not aware of any instances where this vulnerability has been exploited for malicious purposes. Potentially affected users were notified of the flaw in advance, on July 31.

Related: Two Vulnerabilities Patched in BIND DNS Software

Related: DNS Servers Crash Due to BIND Security Flaw

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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.