DNSBomb attack in Unbound

Published: 2024-05-12
Risk Medium
Patch available YES
Number of vulnerabilities 1
CVE-ID CVE-2024-33655
Exploitation vector Network
Public exploit N/A
Vulnerable software
Server applications / DNS servers

Vendor NLnet Labs

Security Bulletin

This security bulletin contains one medium risk vulnerability.

1) Resource management error

EUVDB-ID: #VU89361

Risk: Medium

CVSSv3.1: 5.1 [CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:L/E:U/RL:O/RC:C]

CVE-ID: CVE-2024-33655

CWE-ID: CWE-399 - Resource Management Errors

Exploit availability: No


The vulnerability allows a remote attacker to perform a denial of service (DoS) attack.

The vulnerability exists due to way Unbound queues DNS requests, which makes it susceptible to DNSBomb attack. A remote attacker with ability to control the delay of the malicious authoritative answers can force Unbound to slowly accumulate pending answers for the spoofed addresses. When the authoritative answers become available to Unbound at the same time, Unbound starts serving all the accumulated queries. This results in large-sized, concentrated response bursts to the spoofed addresses.

Unbound itself is not vulnerable for DoS, rather it can be used to take part in a pulsing DoS amplification attack.


Install updates from vendor's website.

Vulnerable software versions

Unbound: 1.0.0 - 1.20.0 rc1

External links


Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

How the attacker can exploit this vulnerability?

The attacker would have to send a specially crafted request to the affected application in order to exploit this vulnerability.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.