The Internet Systems Consortium (ISC) announced this week that updates released for the DNS software BIND patch several denial-of-service (DoS) vulnerabilities that can be exploited remotely.
BIND versions 9.9.9-P8, 9.10.4-P8 and 9.11.0-P5 address three new security holes that could lead to an assertion failure.
The most serious of the flaws, with a “high” severity rating and a CVSS score of 7.5, is CVE-2017-3137. The vulnerability allows an attacker to cause a DoS condition, and it mainly affects recursive resolvers, but authoritative servers could also be vulnerable if they perform recursion.
“A server which is performing recursion can be forced to exit with an assertion failure if it can be caused to receive a response containing CNAME or DNAME resource records with certain ordering,” ISC said in its advisory.
Another vulnerability patched with the latest BIND updates is CVE-2017-3136, a medium severity issue that affects servers configured to use DNS64 with the “break-dnssec yes;” option.
The third flaw, CVE-2017-3138, can be exploited to cause the BIND name server (named) process to exit by sending it a null command string on its control channel. However, the flaw can only be exploited remotely from hosts that are allowed access to the control channel.
ISC said there was no evidence that any of these vulnerabilities had been exploited in the wild.
BIND vulnerable to new reflection attacks
Earlier this month, Ixia security software engineer Oana Murarasu reported finding a new DDoS attack amplification method. The expert discovered that BIND’s recursive DNS resolver allows reflection attacks through root DNAME query responses.
“This amplification attack generates responses 10 or more times larger than the query sent,” Murarasu explained. “For every 1 megabit of traffic sent, 10 megabits is sent to the victim.”
The issue has been reported to ISC, but the organization determined that these attacks are possible due to a protocol design flaw and not a vulnerability in BIND itself. Ixia said Microsoft’s DNS server is not susceptible to such attacks.