UNBOUND

Non-Responsive Delegation Attack

A vulnerability named 'Non-Responsive Delegation Attack' (NRDelegation Attack) has been discovered in various DNS resolving software. The NRDelegation Attack works by having a malicious delegation with a considerable number of non responsive nameservers. The attack starts by querying a resolver for a record that relies on those unresponsive nameservers.

The attack can cause a resolver to spend a lot of time/resources resolving records under a malicious delegation point where a considerable number of unresponsive NS records reside. It can trigger high CPU usage in some resolver implementations that continually look in the cache for resolved NS records in that delegation. This can lead to degraded performance and eventually denial of service in orchestrated attacks.

Unbound does not suffer from high CPU usage, but resources are still needed for resolving the malicious delegation. Unbound will keep trying to resolve the record until hard limits are reached. Based on the nature of the attack and the replies, different limits could be reached.

From version 1.16.3 on, Unbound introduces fixes for better performance when under load, by cutting opportunistic queries for nameserver discovery and DNSKEY prefetching and limiting the number of times a delegation point can issue a cache lookup for missing records.

Unbound 1.16.3 contains a patch. If you cannot upgrade you can also apply the patch manually. To do this, apply the patch on the Unbound source directory with patch -p1 < patch_CVE-2022-3204.diff and then run make install to install Unbound.

Novel "ghost domain names" attack by updating almost expired delegation information

NLnet Labs Unbound, up to and including version 1.16.1, is vulnerable to a novel type of the "ghost domain names" attack. The vulnerability works by targeting an Unbound instance. Unbound is queried for a rogue domain name when the cached delegation information is about to expire. The rogue nameserver delays the response so that the cached delegation information is expired. Upon receiving the delayed answer containing the delegation information, Unbound overwrites the now expired entries. This action can be repeated when the delegation information is about to expire making the rogue delegation information ever-updating. From version 1.16.2 on, Unbound stores the start time for a query and uses that to decide if the cached delegation information can be overwritten.

Unbound 1.16.2 contains a patch. If you cannot upgrade you can also apply the patch manually. To do this, apply the patch on the Unbound source directory with patch -p1 < patch_CVE-2022-30698_CVE-2022-30699.diff and then run make install to install Unbound.

This is a shared patch with CVE-2022-30698 below

Novel "ghost domain names" attack by introducing subdomain delegations

NLnet Labs Unbound, up to and including version 1.16.1 is vulnerable to a novel type of the "ghost domain names" attack. The vulnerability works by targeting an Unbound instance. Unbound is queried for a subdomain of a rogue domain name. The rogue nameserver returns delegation information for the subdomain that updates Unbound's delegation cache. This action can be repeated before expiry of the delegation information by querying Unbound for a second level subdomain which the rogue nameserver provides new delegation information. Since Unbound is a child-centric resolver, the ever-updating child delegation information can keep a rogue domain name resolvable long after revocation. From version 1.16.2 on, Unbound checks the validity of parent delegation records before using cached delegation information.

Unbound 1.16.2 contains a patch. If you cannot upgrade you can also apply the patch manually. To do this, apply the patch on the Unbound source directory with patch -p1 < patch_CVE-2022-30698_CVE-2022-30699.diff and then run make install to install Unbound.

This is a shared patch with CVE-2022-30699 above

Local symlink attack

Unbound when writing and later chown'ing the PID file would not check if an existing file was a symlink. This is a local vulnerability that could create a Denial of Service of the system Unbound is running on. It requires an attacker having access to the limited permission user Unbound runs as and point through the symlink to a critical file on the system.

Unbound 1.13.0 contains a patch. If you cannot upgrade you can also apply the patch manually. To do this, apply the patch on the Unbound source directory with patch -p1 < patch_cve-2020-28935_unbound.diff and then run make install to install Unbound.

Vulnerability in Domain Parse

Fuzzing of the Unbound code made us aware of issues in the parser of received answers. Malformed answers received from upstream servers can result in Unbound entering an infinite loop and thereby becoming unresponsive. When compiled with --enable-debug it is also possible to trigger an assertion, resulting in Unbound to crash.

Unbound 1.10.1 contains a patch. If you cannot upgrade you can also apply the patch manually. To do this, apply the patch on Unbound source directory with patch -p1 < filename, then run make install to install Unbound.

NXNSAttack

Researchers from Tel Aviv University discovered an issue in Unbound and other DNS resolvers that makes it possible to have a single incoming query result in a large number of outgoing queries. This amplification makes it possible for Unbound to be used in a denial of service attack. The researchers discovering this called this attack the NXNSattack.

This attack makes use of cache bypassing using random subdomains in the NSDNAME in NS records. When these delegation records are received during iteration, and the answer does not contain glue records, a resolver has to send out a query to the get the IP address for one of the names. When this query fails (for example because the random name does not exist) a resolver will try the next one. A large set of NS records with random names can result in a large number of outgoing queries going to the same target. More details about this attack will be available in the research paper.

Unbound 1.10.1 contains a patch. If you cannot upgrade you can also apply the patch manually. To do this, apply the patch on Unbound source directory with patch -p1 < filename, then run make install to install Unbound.

Vulnerability in IPSEC module

Due to unsanitized characters passed to the ipsecmod-hook shell command, it is possible for Unbound to allow shell code execution from a specially crafted IPSECKEY answer.

This issue can only be triggered when all of the below conditions are met:

• unbound was compiled with --enable-ipsecmod support, and
• ipsecmod is enabled and used in the configuration (either in the configuration file or using unbound-control), and
• a domain is part of the ipsecmod-whitelist (if ipsecmod-whitelist is used), and
• unbound receives an A/AAAA query for a domain that has an A/AAAA record(s) and an IPSECKEY record(s) available.

The shell code execution can then happen if either the qname or the gateway field of the IPSECKEY (when gateway type == 3) contain a specially crafted domain name.

Unbound 1.9.5 contains a patch. If you cannot upgrade you can also apply the patch manually. To do this, apply the patch on Unbound source directory with patch -p1 < filename, then run make install to install Unbound.

Vulnerability in parsing NOTIFY queries

Due to an error in parsing NOTIFY queries, it is possible for Unbound to continue processing malformed queries and may ultimately result in a pointer dereference in uninitialized memory. This results in a crash of the Unbound daemon.

Unbound 1.9.4 contains a patch. If you cannot upgrade you can also apply the patch manually. To do this, apply the patch on Unbound source directory with patch -p0 < filename, then run make install to install Unbound.

Vulnerability in the processing of wildcard synthesized NSEC records

We discovered a vulnerability in the processing of wildcard synthesized NSEC records. While synthesis of NSEC records is allowed by RFC4592, these synthesized owner names should not be used in the NSEC processing. This does, however, happen in Unbound 1.6.7 and earlier versions.

Unbound 1.6.8 contains a patch. If you cannot upgrade you can also apply the patch manually. To do this, apply the patch on Unbound source directory with patch -p0 < filename, then run make install to install Unbound.

A special thanks goes out to Karst Koymans (University of Amsterdam) for sparking the discovery of this vulnerability by Ralph Dolmans (NLnet Labs).

Ghost domain names attack

The resolver in Unbound before 1.4.11 overwrites cached server names and TTL values in NS records during the processing of a response to an A record query, which allows remote attackers to trigger continued resolvability of revoked domain names via a "ghost domain names" attack. To resolve this issue, upgrade to a newer version of Unbound.

Incorrect proof processing for NSEC3-signed zone

validator/val_nsec3.c in Unbound before 1.4.13p2 does not properly perform proof processing for NSEC3-signed zones, which allows remote DNS servers to cause a denial of service (daemon crash) via a malformed response that lacks expected NSEC3 records, a different vulnerability than CVE-2011-4528.

Unbound 1.4.14 contains a patch, but 1.4.14rc1 is vulnerable. If you cannot upgrade you can also apply a patch. For unbound version 1.4.0 - 1.4.13, apply this patch and for version 1.0.1 - 1.3.4 use this patch. To do this, apply the patch on Unbound source directory with patch -p0 < filename, then run make install to install Unbound.

Processing of duplicate CNAME records in a signed zone

Unbound crashes when confronted with a non-standard response from a server for a domain. This domain produces duplicate RRs from a certain type and is DNSSEC signed. Unbound also crashes when confronted with a query that eventually, and under specific circumstances, resolves to a domain that misses expected NSEC3 records.

Unbound 1.4.14 contains a patch, but 1.4.14rc1 is vulnerable. If you cannot upgrade you can also apply a patch. For unbound version 1.4.0 - 1.4.13, apply this patch and for version 1.0.1 - 1.3.4 use this patch. To do this, apply the patch on Unbound source directory with patch -p0 < filename, then run make install to install Unbound.