What is CVE-2026-81642?

CVE-2026-81642 is Heap buffer overflow and possible Remote Code Execution when digesting DNSKEY. The supplied enrichment data classifies it as Memory Corruption mapped to CWE-122 Heap-based Buffer Overflow.

Which versions are affected?

Affected product and version evidence is listed in the product table above. Current public advisories should be checked for exact version scope before patch targeting is finalized.

Is there active exploitation?

Active exploitation is not confirmed from current sources for CVE-2026-81642. If exploitation is not confirmed from current sources, teams should document that status and continue monitoring KEV, vendor, and telemetry updates.

No. CVE-2026-81642 is not listed in CISA KEV in the supplied enrichment data. KEV status should be monitored because it can change after initial disclosure or after exploitation becomes publicly confirmed.

Is there a public exploit?

1 public PoC repositories reported; 0 marked weaponized in current dataset. Public exploit or PoC availability should raise triage priority, especially for exposed or business-critical systems.

How can defenders detect it?

Start with web/proxy/WAF logs, application logs, network IDS/IPS where available. Look for vulnerability-class behavior, product errors, suspicious authentication events, exploit probes, and abnormal process activity based only on evidence that applies to the affected product.

How should teams prioritize it?

Prioritize CVE-2026-81642 using CVSS 9.1, EPSS 0%, KEV status, public PoC status, and asset exposure. Internet-facing, privileged, or business-critical deployments should be handled first.

Are workarounds available?

Workarounds are not confirmed from current sources. Fixed-version evidence is listed in the mitigation section above.

Which threat actors are linked publicly?

No public threat actor linkage is confirmed from current sources. Do not attribute exploitation to a threat actor unless the source evidence explicitly supports that linkage.

What should be done in the next 24 hours?

Identify exposed assets running affected vendor/product/version combinations. Prioritize based on EPSS, PoC availability, and external exposure. Search available logs for exploit probes, errors, authentication anomalies, or suspicious child processes matching the vulnerability class. Open remediation tickets with affected assets, owners, evidence status, and detection coverage so decisions are traceable.

criticalMemory Corruptionpublic exploit

CVE-2026-81642

CVE-2026-81642 — Heap buffer overflow and possible Remote Code Execution when digesting DNSKEY

In NLnet Labs Unbound up to and including 1.26.0, a vulnerability was found in the DNSSEC validator that enables denial of service and possible remote code execution as a result of digesting DNSKEYs. A DNSKEY with an owner compression pointer to its own RDATA can overflow the digest buffer. Remote code execution is possible through attacker controlled data. An adversary can exploit the vulnerability by controlling a malicious zone and querying a vulnerable Unbound.

Published Sep 16, 2026Updated Sep 16, 2026Sources: NVD, NLnet Labs (CNA), GitHub, GitHub Security Advisory, SOCRadar CTI

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the scoring sources call it.

Exploitation

Exploit code

public exploit, none observed

EPSS

ahead of 0% of scored CVEs

Affects

NLnet Labs

Unbound

CVSS base

9.1

critical

CISA SSVC assessment

Three decision points CISA publishes for the CVEs it assesses · SSVC 2.0.3. A stakeholder decision, not a severity score.

CISA

Exploitation

None

none · proof-of-concept · active

Automatable

Yes

can an attacker script all four kill-chain steps

Technical impact

Total

partial · total control of the vulnerable component

Remediation

The vendor's own words where we have them.

This issue is fixed starting with version 1.26.1

First 24 hours

Ordered from the record's own fields — exposure first, because you cannot patch what you have not found.

Identify exposed assets running affected vendor/product/version combinations.
Prioritize based on EPSS, PoC availability, and external exposure.
Search available logs for exploit probes, errors, authentication anomalies, or suspicious child processes matching the vulnerability class.

Affected scope

Vendor, product and version as the advisories word them.

Vendor	Product	Versions	Status
NLnet Labs	Unbound	0 to < 1.26.1	Vulnerable

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack Complexity

Low

Attack Vector

Network

Privileges Req

None

User Interaction

None

Every base score collected

Sources score independently and disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Source
9.1	CVSS 4.0	critical	—	—	NLnet Labs (CNA)

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/E:U/U:Red

What this weakness leads to

MITRE's own consequences and mitigations for the weakness class — the authority's wording, not guidance derived from the CVSS vector.

MITRE

CWE-122 · Heap-based Buffer Overflow

DoS: Crash, Exit, or Restart
DoS: Resource Consumption (CPU)
DoS: Resource Consumption (Memory)
Execute Unauthorized Code or Commands

Mitigation: Pre-design: Use a language or compiler that performs automatic bounds checking.

Weakness & attack patterns

CWE-122Heap-based Buffer Overflow

Attack patterns reported against this CVE. The ATT&CK techniques below are inferred from its weakness class.

CAPEC-92 · Forced Integer Overflow

Public exploit

Capability, not use: code existing is a different claim from anyone running it.

Exploit entries

Exploit-DB and CTI exploit indexes

Detection

Read off the CVSS vector and the weakness class. Starting points, not rules we have tested.

Prioritize edge telemetry for network-reachable Unbound.
Monitor for scanner or exploit-pattern traffic after 1 public PoC repositories were reported.

web/proxy/WAF logsapplication logsnetwork IDS/IPS

Timeline

What happened to this CVE, newest first — with the readings a source repeats on a schedule counted underneath rather than listed.

2026
Added · CVSS 3.1 9.1 (AV:N)
Sep 16, 2026 · NVD
Initial · CVE published
Sep 16, 2026 · NVD
Reported · Fixes released with version 1.26.1
Sep 16, 2026 · NLnet Labs
Added · GHSA-xxc4-rpp8-3fw7 published (critical)
Sep 16, 2026 · GitHub Security Advisory
CVE published by MITRE.
Sep 16, 2026 · SOCRadar CTI
Reported · Yuqi Qiu verifies patch
Aug 13, 2026 · NLnet Labs
Reported · NLnet Labs shares patch
Aug 12, 2026 · NLnet Labs
Issue reported by Yuqi Qiu
Aug 11, 2026 · NLnet Labs

References

3 on the record

www.nlnetlabs.nl/downloads/unbound/CVE-2026-81642.txt
Vendor Advisory
nvd.nist.gov/vuln/detail/CVE-2026-81642
NVD
github.com/advisories/GHSA-xxc4-rpp8-3fw7
Exploit, Third Party Advisory

Coverage

1 story from the feeds we poll

Critical Unbound DNSSEC Validator Flaw Could Allow RCE via a Malicious DNS Zone
The Hacker News · Sep 17, 2026

Elsewhere on this site

NLnet Labsevery CVE for this vendor
Memory Corruptionsame class
CWE-122other pages naming this weakness

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record1

What should defenders know first?

CVE-2026-81642 is Heap buffer overflow and possible Remote Code Execution when digesting DNSKEY, a critical vulnerability affecting Unbound from NLnet Labs. The current evidence does not list it in CISA KEV, and the exploit status is: Active exploitation is not confirmed from current sources for CVE-2026-81642. Public exploit evidence is: 1 public PoC repositories reported; 0 marked weaponized in current dataset. The affected-version evidence is listed in the key facts and affected products tables. Defenders should first verify whether exposed or business-critical assets run those versions, then apply vendor patches or mitigations, restrict reachable attack surface, and preserve logs for detection review. CVSS 9.1 describes technical severity, while EPSS 0% helps estimate near-term exploit likelihood; neither replaces asset context. Unknown fields should remain explicit in tickets, and threat actor, IOC, victimology, or payload claims should not be added unless a cited source supports them. Monitor CISA KEV, vendor advisories, NVD changes, public PoC repositories, and internal telemetry for update triggers.