Security Experts:

Critical DoS Flaw Patched in BIND

The Internet Systems Consortium (ISC) announced on Tuesday the availability of BIND updates that address several vulnerabilities, including a remotely exploitable denial-of-service (DoS) issue that has been rated critical.

BIND versions 9.10.3-P2, 9.9.8-S3 and 9.9.8-P2 address three new vulnerabilities. The most serious of them is a flaw that can be exploited to launch DoS attacks against servers performing recursive queries (CVE-2015-8000).

“An attacker who can cause a server to request a record with a malformed class attribute can use this bug to trigger a REQUIRE assertion in db.c, causing named to exit and denying service to clients,” ISC noted in its advisory. “The risk to recursive servers is high. Authoritative servers are at limited risk if they perform authentication when making recursive queries to resolve addresses for servers listed in NS RRSETs.”

The issue affects BIND versions 9.0.x through 9.9.8 and 9.10.0 through 9.10.3. The vulnerability is remotely exploitable and has been rated critical, but ISC says it’s not aware of any active exploits.

Another security hole patched in the latest versions of the popular DNS software is a medium severity race condition triggered when handling socket errors (CVE-2015-8461). The flaw can cause a server to exit when encountering an INSIST assertion failure in the “resolver.c” library.

“An uncommonly occurring condition can cause affected servers to exit with an INSIST failure depending on the outcome of a race condition in resolver.c While difficult to exploit reliably, a malicious party could, through deliberate behavior, significantly increase the probability of encountering the triggering condition, resulting in denial-of-service to clients if successful,” ISC said.

The latest BIND updates also fix an OpenSSL vulnerability (CVE-2015-3193) patched by the OpenSSL Project in early December. The flaw is related to the “BN_mod_exp” function, which could produce incorrect results on x86_64 systems.

While there is no evidence that any of these security holes have been exploited in the wild, attacks targeting DNS servers running BIND are not unheard of. In August, researchers reported seeing attacks that leveraged a DoS vulnerability patched just a few days earlier.

Related: BIND Updates Patch Two Critical Vulnerabilities

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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.