The Internet Systems Consortium (ISC) has released patches for three remotely exploitable denial-of-service (DoS) vulnerabilities in the DNS software suite BIND.
Tracked as CVE-2023-2828, CVE-2023-2829 and CVE-2023-2911, these high-severity issues could be exploited to exhaust the available memory, or could cause named – BIND’s daemon that functions both as a recursive resolver and as an authoritative name server – to crash.
CVE-2023-2828, ISC explains in an advisory, impacts a named function responsible for cleaning the memory cache to prevent it from reaching the maximum allowed value (the default is 90% of the total amount of memory available on the host).
“It has been discovered that the effectiveness of the cache-cleaning algorithm used in named can be severely diminished by querying the resolver for specific RRsets in a certain order,” ISC notes.
An attacker can exploit the vulnerability to cause the amount of memory used by named to exceed the maximum allowed amount. If the default configuration is used, the attacker could exhaust all available memory on the host, causing a DoS condition.
The second flaw, CVE-2023-2829, only impacts named instances “configured to run as a DNSSEC-validating recursive resolver with the Aggressive Use of DNSSEC-Validated Cache (RFC 8198) option enabled”.
A remote attacker could send specific queries to the resolver, causing named to terminate unexpectedly. The vulnerable option is enabled by default in BIND versions 9.18 and 9.18-S and newer but was disabled in earlier versions, unless enabled explicitly. Turning the option off prevents the issue.
The third bug, CVE-2023-2911, impacts BIND 9 resolvers that reach the quota of recursive clients, if they are configured to return ‘stale’ cached answers with the ‘stale-answer-client-timeout 0;’ option.
The flaw can be triggered with a sequence of serve-stale-related lookups, causing named to loop and crash. The vulnerability can be prevented by changing the value of ‘stale-answer-client-timeout’.
“Users of versions 9.18.10, 9.16.36, 9.16.36-S1 or older who are unable to upgrade should set stale-answer-client-timeout to off; using a non-zero value with these older versions leaves named vulnerable to CVE-2022-3924,” ISC explains.
All three vulnerabilities were addressed with the release of BIND versions 9.16.42, 9.18.16, and 9.19.14, and BIND Supported Preview Edition versions 9.16.42-S1 and 9.18.16-S1.
ISC says it is not aware of any of these flaws being exploited in attacks.
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