Security Experts:

DNS Servers Crash Due to BIND Security Flaw

Updates released by the Internet Systems Consortium (ISC) for BIND patch a remotely exploitable security flaw that has caused some DNS servers to crash.

The high severity vulnerability, tracked as CVE-2017-3145, is caused by a use-after-free bug that can lead to an assertion failure and crash of the BIND name server (named) process.

“BIND was improperly sequencing cleanup operations on upstream recursion fetch contexts, leading in some cases to a use-after-free error that can trigger an assertion failure and crash in named,” ISC said in an advisory.

While there is no evidence that this vulnerability has been exploited in malicious attacks, ISC says crashes caused by the bug have been reported by “multiple parties.” The impacted systems act as DNSSEC validating resolvers, and temporarily disabling DNSSEC validation can be used as a workaround.

The vulnerability, discovered by Jayachandran Palanisamy of Cygate AB, affects BIND versions 9.9.9-P8 to 9.9.11, 9.10.4-P8 to 9.10.6, 9.11.0-P5 to 9.11.2, 9.9.9-S10 to 9.9.11-S1, 9.10.5-S1 to 9.10.6-S1, and 9.12.0a1 to 9.12.0rc1. It has been patched with the release of BIND 9.9.11-P1, 9.10.6-P1, 9.11.2-P1 and 9.12.0rc2.

“Addresses could be referenced after being freed during resolver processing, causing an assertion failure. The chances of this happening were remote, but the introduction of a delay in resolution increased them. (The delay will be addressed in an upcoming maintenance release.),” ISC explained.

The organization has also informed users of CVE-2017-3144, a medium severity DHCP vulnerability affecting versions 4.1.0 to 4.1-ESV-R15, 4.2.0 to 4.2.8, and 4.3.0 to 4.3.6.

“By intentionally exploiting this vulnerability an attacker who is permitted to establish connections to the OMAPI control port can exhaust the pool of socket descriptors available to the DHCP server,” ISC explained.

“Once exhausted, the server will not accept additional connections, potentially denying access to legitimate connections from the server operator. While the server will continue to receive and service DHCP client requests, the operator can be blocked from the ability to use OMAPI to control server state, add new lease reservations, etc.,” it added.

ISC has developed a patch and it plans on adding it to a future maintenance release of DHCP. In the meantime, users can protect themselves against potential attacks by disallowing access to the OMAPI control port from unauthorized clients. Alternatively, organizations can obtain the patch from ISC and integrate it into their own code.

Related: Authentication Bypass Flaw Patched in BIND, Knot DNS

Related: Critical Flaw Patched in BIND Installer for Windows

Related: Potentially Serious DoS Flaw Patched in BIND

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Eduard Kovacs 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.