VulnerabilityPublished 16 Sep 2026Updated 11 Nov 2026

CVE-2026-85501: Unbound · Novel vulnerabilities to launch algorithmic complexity attacks on DNSSEC have been

Affects unboundSource GCVE Database

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Authoritative record:CVE-2026-85501· Medium 5.3

Not known to be exploited · CVSS 5.3 Medium · fixed in 1.4.22-1ubuntu4.14.04.3+esm5 : update unbound when convenient.

Data as of 11 Nov 2026, 13:09 UTC

CVSS 3.1 base score

5.3Medium

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

Patch: Available – fixed in 1.4.22-1ubuntu4.14.04.3+esm5, 1.5.8-1ubuntu1.1+esm5, 1.6.7-1ubuntu2.6+esm6 +5

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

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

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: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 16 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: 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 11 Nov 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.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), 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

Upgrade to a fixed release listed under Affected software.

Patches and advisories

Affected software

Product	Affected	Fixed in
Ubuntu 26.10unbound`pkg:deb/ubuntu/unbound?arch=source&distro=stonking`Other threats	Affected <1.25.1-1ubuntu3.1	Fixed in 1.25.1-1ubuntu3.1
Ubuntu 26.04 LTSunbound`pkg:deb/ubuntu/unbound?arch=source&distro=resolute`Other threats	Affected <1.24.2-1ubuntu2.4	Fixed in 1.24.2-1ubuntu2.4
Ubuntu 24.04 LTSunbound`pkg:deb/ubuntu/unbound?arch=source&distro=noble`Other threats	Affected <1.19.2-1ubuntu3.12	Fixed in 1.19.2-1ubuntu3.12
Ubuntu 22.04 LTSunbound`pkg:deb/ubuntu/unbound?arch=source&distro=jammy`Other threats	Affected <1.13.1-1ubuntu5.17	Fixed in 1.13.1-1ubuntu5.17
Ubuntu Pro 20.04 LTSunbound`pkg:deb/ubuntu/unbound?arch=source&distro=esm-infra/focal`Other threats	Affected <1.9.4-2ubuntu1.11+esm3	Fixed in 1.9.4-2ubuntu1.11+esm3
Ubuntu Pro 18.04 LTSunbound`pkg:deb/ubuntu/unbound?arch=source&distro=esm-infra/bionic`Other threats	Affected <1.6.7-1ubuntu2.6+esm6	Fixed in 1.6.7-1ubuntu2.6+esm6

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Fixed versions of Unbound are available and should be applied to remediate these vulnerabilities. The fixed versions include 1.4.22-1ubuntu4.14.04.3+esm5, 1.5.8-1ubuntu1.1+esm5, 1.6.7-1ubuntu2.6+esm6, 1.9.4-2ubuntu1.11+esm3, 1.13.1-1ubuntu5.17, and later releases. Users should upgrade to these versions or later to mitigate the risk. Refer to the Ubuntu security notices USN-8946-1 and USN-8946-2 for detailed patch information. No known exploits are reported in the wild at this time.

Description

Unbound DNS resolver versions up to 1.26.0 contain vulnerabilities collectively termed 'ReTrap' that enable algorithmic complexity attacks on DNSSEC validation. These attacks exploit mechanisms such as triple matching of Zone, Algo, and KeyTag (TagTrap), iterative chain-of-trust validation for deeply nested domains (DelegationTrap), excessive invalid NSEC records (NsecTrap), and validation of the ADDITIONAL section (AdditionalTrap). Exploitation results in significant computational overhead and degradation of service. Fixed versions addressing these issues have been released.

References

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