A high severity denial-of-service (DoS) vulnerability patched last month in the popular DNS software BIND has been exploited in the wild to crash systems.
The vulnerability, discovered by the Internet Systems Consortium (ISC) and tracked as CVE-2016-2776, was patched in late September with the release of BIND 9.9.9-P3, 9.10.4-P3 and 9.11.0rc3. The security hole can be exploited for DoS attacks using specially crafted DNS packets.
On October 4, shortly after proof-of-concept (PoC) code and a Metasploit module were made available, the ISC announced that it had learned of server crashes apparently resulting from exploitation of this vulnerability. Japan’s National Police Agency also issued an alert to warn users of “indiscriminate attacks.”
The vulnerability is related to how a DNS server constructs a response to certain queries. If the response to a query has a size larger than the default 512, it can lead to a crash of the BIND name server (named) process.
In a blog post published on Wednesday, security firm Trend Micro described the cause of the vulnerability as follows:
“When a DNS server constructs a response for a DNS Query, it reserves the space in the response buffer (of size 512 by default), it will increment the msg->reserved by the size required for Answer RR. The size also adds up in msg->reserved size, which would be the same if the response buffer has other Resource Records.
Before patching, the server does not take fixed 12-byte DNS headers into consideration, which also adds to the response traffic after rendering the Resource Records from Query through function dns_message_rendersection(). So if the DNS response(r.length) traffic is less than 512 bytes (msg->reserved), the function will return true, but adding the fixed 12-byte header will cause the service to terminate if it exceeds the fixed reserved size of 512 bytes.”
Researchers at Infobyte, who published the PoC exploit and the Metasploit module, believe that the use of the msg->reserved variable could introduce other vulnerabilities similar to CVE-2016-2776.
This is not the first time DNS servers have been targeted with a DoS flaw in BIND. Last year, researchers warned that a critical vulnerability that had the potential to cause serious disruption (CVE-2015-5477) was exploited in the wild.
Related: DoS Vulnerability Patched in BIND