Nlnetlabs Unbound

Unbound 1.24.0 DNS Resolver Poisonable NS RRSets Possible Domain Hijack
CVE-2025-11411 - October 22, 2025

NLnet Labs Unbound up to and including version 1.24.1 is vulnerable to possible domain hijack attacks. Promiscuous NS RRSets that complement positive DNS replies in the authority section can be used to trick resolvers to update their delegation information for the zone. Usually these RRSets are used to update the resolver's knowledge of the zone's name servers. A malicious actor can exploit the possible poisonous effect by injecting NS RRSets (and possibly their respective address records) in a reply. This could be done for example by trying to spoof a packet or fragmentation attacks. Unbound would then proceed to update the NS RRSet data it already has since the new data has enough trust for it, i.e., in-zone data for the delegation point. Unbound 1.24.1 includes a fix that scrubs unsolicited NS RRSets (and their respective address records) from replies mitigating the possible poison effect. Unbound 1.24.2 includes an additional fix that scrubs unsolicited NS RRSets (and their respective address records) from YXDOMAIN and non-referral nodata replies, further mitigating the possible poison effect.

Acceptance of Extraneous Untrusted Data With Trusted Data

Unbound Recursor ECS Spoofing Mitigation via out.edns_subnet_harden
CVE-2025-30192 - July 21, 2025

An attacker spoofing answers to ECS enabled requests sent out by the Recursor has a chance of success higher than non-ECS enabled queries. The updated version include various mitigations against spoofing attempts of ECS enabled queries by chaining ECS enabled requests and enforcing stricter validation of the received answers. The most strict mitigation done when the new setting outgoing.edns_subnet_harden (old style name edns-subnet-harden) is enabled.

Unbound DNS DDoS via Unbounded Name Compression 1.21.0
CVE-2024-8508 5.3 - Medium - October 03, 2024

NLnet Labs Unbound up to and including version 1.21.0 contains a vulnerability when handling replies with very large RRsets that it needs to perform name compression for. Malicious upstreams responses with very large RRsets can cause Unbound to spend a considerable time applying name compression to downstream replies. This can lead to degraded performance and eventually denial of service in well orchestrated attacks. The vulnerability can be exploited by a malicious actor querying Unbound for the specially crafted contents of a malicious zone with very large RRsets. Before Unbound replies to the query it will try to apply name compression which was an unbounded operation that could lock the CPU until the whole packet was complete. Unbound version 1.21.1 introduces a hard limit on the number of name compression calculations it is willing to do per packet. Packets that need more compression will result in semi-compressed packets or truncated packets, even on TCP for huge messages, to avoid locking the CPU for long. This change should not affect normal DNS traffic.

Improper Validation of Specified Quantity in Input

Unbound NULL Pointer Deref in ub_ctx_set_fwd causes DoS
CVE-2024-43167 2.8 - Low - August 12, 2024

DISPUTE NOTE: this issue does not pose a security risk as it (according to analysis by the original software developer, NLnet Labs) falls within the expected functionality and security controls of the application. Red Hat has made a claim that there is a security risk within Red Hat products. NLnet Labs has no further information about the claim, and suggests that affected Red Hat customers refer to available Red Hat documentation or support channels. ORIGINAL DESCRIPTION: A NULL pointer dereference flaw was found in the ub_ctx_set_fwd function in Unbound. This issue could allow an attacker who can invoke specific sequences of API calls to cause a segmentation fault. When certain API functions such as ub_ctx_set_fwd and ub_ctx_resolvconf are called in a particular order, the program attempts to read from a NULL pointer, leading to a crash. This issue can result in a denial of service by causing the application to terminate unexpectedly.

NULL Pointer Dereference

Denial of Service via crafted upstream reply in Unbound Recursor
CVE-2024-25583 - April 25, 2024

A crafted response from an upstream server the recursor has been configured to forward-recurse to can cause a Denial of Service in the Recursor. The default configuration of the Recursor does not use recursive forwarding and is not affected.

Unbound DNS OOB Memory Corruption via Malicious Response
CVE-2024-27227 9.8 - Critical - March 11, 2024

A malicious DNS response can trigger a number of OOB reads, writes, and other memory issues

Memory Corruption

Denial of Service via Infinite Loop in Unbound EDE Record Trimming 1.18.0-1.19.1
CVE-2024-1931 7.5 - High - March 07, 2024

NLnet Labs Unbound version 1.18.0 up to and including version 1.19.1 contain a vulnerability that can cause denial of service by a certain code path that can lead to an infinite loop. Unbound 1.18.0 introduced a feature that removes EDE records from responses with size higher than the client's advertised buffer size. Before removing all the EDE records however, it would try to see if trimming the extra text fields on those records would result in an acceptable size while still retaining the EDE codes. Due to an unchecked condition, the code that trims the text of the EDE records could loop indefinitely. This happens when Unbound would reply with attached EDE information on a positive reply and the client's buffer size is smaller than the needed space to include EDE records. The vulnerability can only be triggered when the 'ede: yes' option is used; non default configuration. From version 1.19.2 on, the code is fixed to avoid looping indefinitely.

Infinite Loop

Unbound Unprivileged Process Alters Runtime Config via Default Permissions
CVE-2024-1488 8 - High - February 15, 2024

A vulnerability was found in Unbound due to incorrect default permissions, allowing any process outside the unbound group to modify the unbound runtime configuration. If a process can connect over localhost to port 8953, it can alter the configuration of unbound.service. This flaw allows an unprivileged attacker to manipulate a running instance, potentially altering forwarders, allowing them to track all queries forwarded by the local resolver, and, in some cases, disrupting resolving altogether.

Incorrect Default Permissions

DNSSEC KeyTrap DoS via DNSKEY/RRSIG overevaluation in BIND 9
CVE-2023-50387 7.5 - High - February 14, 2024

Certain DNSSEC aspects of the DNS protocol (in RFC 4033, 4034, 4035, 6840, and related RFCs) allow remote attackers to cause a denial of service (CPU consumption) via one or more DNSSEC responses, aka the "KeyTrap" issue. One of the concerns is that, when there is a zone with many DNSKEY and RRSIG records, the protocol specification implies that an algorithm must evaluate all combinations of DNSKEY and RRSIG records.

Allocation of Resources Without Limits or Throttling

Unbound 1.16.3: NRDelegation DNS Resolver DoS
CVE-2022-3204 7.5 - High - September 26, 2022

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.

Resource Exhaustion

Unbound <=1.16.1 Vulnerable to Ghost Domain Names Attack
CVE-2022-30699 6.5 - Medium - August 01, 2022

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.

Insufficient Session Expiration

Unbound <=1.16.1 Vulnerable to Ghost Domain Names Attack
CVE-2022-30698 6.5 - Medium - August 01, 2022

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.

Insufficient Session Expiration

Unbound before 1.9.5 allows an integer overflow in the regional allocator via the ALIGN_UP macro
CVE-2019-25033 - April 27, 2021

Unbound before 1.9.5 allows an integer overflow in the regional allocator via the ALIGN_UP macro. NOTE: The vendor disputes that this is a vulnerability. Although the code may be vulnerable, a running Unbound installation cannot be remotely or locally exploited

Unbound before 1.9.5 allows an out-of-bounds write via a compressed name in rdata_copy
CVE-2019-25042 - April 27, 2021

Unbound before 1.9.5 allows an out-of-bounds write via a compressed name in rdata_copy. NOTE: The vendor disputes that this is a vulnerability. Although the code may be vulnerable, a running Unbound installation cannot be remotely or locally exploited

Unbound before 1.9.5 allows an infinite loop via a compressed name in dname_pkt_copy
CVE-2019-25040 - April 27, 2021

Unbound before 1.9.5 allows an infinite loop via a compressed name in dname_pkt_copy. NOTE: The vendor disputes that this is a vulnerability. Although the code may be vulnerable, a running Unbound installation cannot be remotely or locally exploited

Unbound before 1.9.5 allows an integer overflow in a size calculation in dnscrypt/dnscrypt.c
CVE-2019-25038 - April 27, 2021

Unbound before 1.9.5 allows an integer overflow in a size calculation in dnscrypt/dnscrypt.c. NOTE: The vendor disputes that this is a vulnerability. Although the code may be vulnerable, a running Unbound installation cannot be remotely or locally exploited

Unbound before 1.9.5 allows an assertion failure and denial of service in dname_pkt_copy via an invalid packet
CVE-2019-25037 - April 27, 2021

Unbound before 1.9.5 allows an assertion failure and denial of service in dname_pkt_copy via an invalid packet. NOTE: The vendor disputes that this is a vulnerability. Although the code may be vulnerable, a running Unbound installation cannot be remotely or locally exploited

Unbound before 1.9.5 allows an assertion failure and denial of service in synth_cname
CVE-2019-25036 - April 27, 2021

Unbound before 1.9.5 allows an assertion failure and denial of service in synth_cname. NOTE: The vendor disputes that this is a vulnerability. Although the code may be vulnerable, a running Unbound installation cannot be remotely or locally exploited

Unbound before 1.9.5 allows an out-of-bounds write in sldns_bget_token_par
CVE-2019-25035 - April 27, 2021

Unbound before 1.9.5 allows an out-of-bounds write in sldns_bget_token_par. NOTE: The vendor disputes that this is a vulnerability. Although the code may be vulnerable, a running Unbound installation cannot be remotely or locally exploited

Unbound before 1.9.5
CVE-2019-25031 - April 27, 2021

Unbound before 1.9.5 allows configuration injection in create_unbound_ad_servers.sh upon a successful man-in-the-middle attack against a cleartext HTTP session. NOTE: The vendor does not consider this a vulnerability of the Unbound software. create_unbound_ad_servers.sh is a contributed script from the community that facilitates automatic configuration creation. It is not part of the Unbound installation

Unbound before 1.9.5 allows an assertion failure via a compressed name in dname_pkt_copy
CVE-2019-25041 - April 27, 2021

Unbound before 1.9.5 allows an assertion failure via a compressed name in dname_pkt_copy. NOTE: The vendor disputes that this is a vulnerability. Although the code may be vulnerable, a running Unbound installation cannot be remotely or locally exploited

Unbound before 1.9.5 allows an integer overflow in a size calculation in respip/respip.c
CVE-2019-25039 - April 27, 2021

Unbound before 1.9.5 allows an integer overflow in a size calculation in respip/respip.c. NOTE: The vendor disputes that this is a vulnerability. Although the code may be vulnerable, a running Unbound installation cannot be remotely or locally exploited

Unbound before 1.9.5 allows an integer overflow in sldns_str2wire_dname_buf_origin, leading to an out-of-bounds write
CVE-2019-25034 - April 27, 2021

Unbound before 1.9.5 allows an integer overflow in sldns_str2wire_dname_buf_origin, leading to an out-of-bounds write. NOTE: The vendor disputes that this is a vulnerability. Although the code may be vulnerable, a running Unbound installation cannot be remotely or locally exploited

Unbound before 1.9.5 allows an integer overflow in the regional allocator via regional_alloc
CVE-2019-25032 - April 27, 2021

Unbound before 1.9.5 allows an integer overflow in the regional allocator via regional_alloc. NOTE: The vendor disputes that this is a vulnerability. Although the code may be vulnerable, a running Unbound installation cannot be remotely or locally exploited

NLnet Labs Unbound, up to and including version 1.12.0, and NLnet Labs NSD, up to and including version 4.3.3, contain a local vulnerability
CVE-2020-28935 5.5 - Medium - December 07, 2020

NLnet Labs Unbound, up to and including version 1.12.0, and NLnet Labs NSD, up to and including version 4.3.3, contain a local vulnerability that would allow for a local symlink attack. When writing the PID file, Unbound and NSD create the file if it is not there, or open an existing file for writing. In case the file was already present, they would follow symlinks if the file happened to be a symlink instead of a regular file. An additional chown of the file would then take place after it was written, making the user Unbound/NSD is supposed to run as the new owner of the file. If an attacker has local access to the user Unbound/NSD runs as, she could create a symlink in place of the PID file pointing to a file that she would like to erase. If then Unbound/NSD is killed and the PID file is not cleared, upon restarting with root privileges, Unbound/NSD will rewrite any file pointed at by the symlink. This is a local vulnerability that could create a Denial of Service of the system Unbound/NSD is running on. It requires an attacker having access to the limited permission user Unbound/NSD runs as and point through the symlink to a critical file on the system.

insecure temporary file

Unbound before 1.10.1 has an infinite loop
CVE-2020-12663 - May 19, 2020

Unbound before 1.10.1 has an infinite loop via malformed DNS answers received from upstream servers.

Unbound before 1.10.1 has Insufficient Control of Network Message Volume, aka an "NXNSAttack" issue
CVE-2020-12662 - May 19, 2020

Unbound before 1.10.1 has Insufficient Control of Network Message Volume, aka an "NXNSAttack" issue. This is triggered by random subdomains in the NSDNAME in NS records.

Unbound 1.6.4 through 1.9.4 contain a vulnerability in the ipsec module
CVE-2019-18934 - November 19, 2019

Unbound 1.6.4 through 1.9.4 contain a vulnerability in the ipsec module that can cause shell code execution after receiving a specially crafted answer. This issue can only be triggered if unbound was compiled with `--enable-ipsecmod` support, and ipsecmod is enabled and used in the configuration.

Unbound before 1.9.4 accesses uninitialized memory, which allows remote attackers to trigger a crash via a crafted NOTIFY query
CVE-2019-16866 - October 03, 2019

Unbound before 1.9.4 accesses uninitialized memory, which allows remote attackers to trigger a crash via a crafted NOTIFY query. The source IP address of the query must match an access-control rule.