VulnerabilityPublished 23 Sep 2022Updated 27 May 2025

CVE-2022-40188: Knot Resolver · Inefficient Algorithmic Complexity

Source CVE Database V5

Not known to be exploited · CVSS 7.5 High · fixed in 5.5.3 : patch affected systems soon.

Data as of 26 Oct 2026, 17:16 UTC

CVSS 3.1 base score

7.5High

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 1.9% chance of exploitation in 30 days – higher than 80% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 5.5.3

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 23 Sep 2022
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
n/a n/a	Affected <5.5.3	Fixed in 5.5.3

AI-suggested

To mitigate CVE-2022-40188, European organizations should prioritize upgrading Knot Resolver installations to version 5.5.3 or later, where the vulnerability has been addressed. If immediate upgrade is not feasible, organizations should consider implementing network-level protections such as rate limiting and filtering of DNS responses containing unusually large NS or address record sets from authoritative servers. Deploying anomaly detection systems to monitor for abnormal CPU usage patterns on DNS resolvers can provide early warning of exploitation attempts. Additionally, organizations should review their DNS resolver exposure to the internet and restrict access to trusted networks where possible. Employing DNS response validation and caching strategies can reduce the processing load on resolvers. Regularly auditing DNS infrastructure configurations and applying security patches promptly will further reduce risk. Finally, maintaining up-to-date incident response plans that include DNS service disruptions will help organizations respond effectively to potential attacks exploiting this vulnerability.

Description

Knot Resolver before 5.5.3 allows remote attackers to cause a denial of service (CPU consumption) because of algorithmic complexity. During an attack, an authoritative server must return large NS sets or address sets.

Impact

For European organizations, the impact of CVE-2022-40188 can be significant, especially for those relying on Knot Resolver as part of their DNS infrastructure. A successful exploitation would lead to denial of service conditions on DNS resolvers, causing delays or failures in domain name resolution. This can disrupt internal and external communications, access to cloud services, and other critical network operations. Organizations in sectors such as finance, telecommunications, government, and critical infrastructure could experience operational outages, impacting business continuity and service availability. While the vulnerability does not compromise data confidentiality or integrity, the availability impact alone can lead to cascading effects, including loss of productivity, customer dissatisfaction, and potential regulatory scrutiny under European data protection and operational resilience frameworks. The lack of known exploits in the wild reduces immediate risk but does not eliminate the threat, as attackers may develop exploits targeting this vulnerability. The attack requires no authentication and can be launched remotely, increasing the attack surface for exposed DNS resolvers.

CWE-407Inefficient Algorithmic Complexity (opens in a new tab)
Class weaknessLikelihood of exploit: Low
An algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached.
OWASP Cheat Sheets
File Upload (opens in a new tab)
OWASP ASVS 4.0.3
V12.1.1 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 6 Jul 2025, 04:11 UTC

WeaknessesCWE-407

Technical details

References

Community reviews

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