REDHAT-BUG-2536382: Medium severity GNU GNU C Library vulnerability
Initializing the DNS stub resolver from an /etc/resolv.conf file, or a LOCALDOMAIN environment variable, whose search list contains a domain of roughly 200 characters or more in the GNU C Library version 2.26 to 2.44 results in an assertion failure which aborts the process.
The resolver truncates the search list when copying it into the fixed-size res.defdname buffer, then asserts that the copy is consistent with the full configuration. The consistency check compared against the wrong size and did not handle a first entry that does not fit, so a correctly truncated list failed the assertion. Any process that resolves names through the library is affected, including long-running processes that reload /etc/resolv.conf on the next query after it changes. Search domains are commonly written to /etc/resolv.conf from data received over DHCP or from a VPN server, so an attacker on the local network may be able to trigger this without privileges on the target system, subject to validation by the network configuration software.
Affected Software
Event History
Frequently Asked Questions
Who can realistically trigger this issue?
An attacker on the local network may be able to trigger it by supplying DNS search-domain data through DHCP or a VPN server, provided the network configuration software accepts and writes that data into /etc/resolv.conf. A LOCALDOMAIN environment variable with a sufficiently long search-list entry can also trigger the condition.
What must occur for an affected process to abort?
The resolver must initialize from /etc/resolv.conf or LOCALDOMAIN containing a search-list domain of roughly 200 characters or more, and the process must perform name resolution through the GNU C Library. Long-running processes can be affected when they reload a changed /etc/resolv.conf on their next DNS query.
What can be done if patching cannot happen immediately?
Prevent untrusted DHCP or VPN-provided search domains from being accepted or written to /etc/resolv.conf, and avoid setting LOCALDOMAIN to a search list containing very long domains. Review network configuration validation for overly long search-list entries.