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

> A heap buffer overflow in Unbound's DNSSEC validator allows remote code execution or denial of service via malicious DNSKEY records.

- **Severity:** Critical 9.1 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 16 Sep 2026
- **Updated:** 16 Sep 2026
- **Also known as:** ALPINE-CVE-2026-81642, AZL-101709, CLSA-2026-1790264021, CLSA-2026-1790264968, CLSA-2026-1790590437, DEBIAN-CVE-2026-81642, ECHO-8edc-ef1d-692f, GHSA-xxc4-rpp8-3fw7, OESA-2026-4130, RHSA-2026:71459, RHSA-2026:71460, RHSA-2026:71610, RHSA-2026:71611, RHSA-2026:72110, RHSA-2026:72183, RHSA-2026:72199, RHSA-2026:72264, ROOT-OS-DEBIAN-12-CVE-2026-81642, UBUNTU-CVE-2026-81642

## What is CVE-2026-81642?

CVE-2026-81642 is a critical memory corruption vulnerability in Nlnetlabs Unbound, published on 16 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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.

Weakness: CWE-122 (Heap-based Buffer Overflow)

## Which versions are affected by CVE-2026-81642?

It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `unbound` | Red Hat:enterprise_linux_eus:10.0 | All versions | 0:1.20.0-18.el10_0.13 |
| `unbound-libs` | Red Hat:enterprise_linux_eus:10.0 | All versions | 0:1.20.0-18.el10_0.13 |
| `unbound` | Red Hat:rhel_aus:8.4::appstream | All versions | 0:1.7.3-15.el8_4.4 |
| `unbound-libs` | Red Hat:rhel_aus:8.4::appstream | All versions | 0:1.7.3-15.el8_4.4 |
| `unbound` | Red Hat:rhel_aus:8.6::appstream | All versions | 0:1.7.3-17.el8_6.8 |
| `unbound-libs` | Red Hat:rhel_aus:8.6::appstream | All versions | 0:1.7.3-17.el8_6.8 |
| `python3-unbound` | Red Hat:rhel_e4s:8.8::appstream | All versions | 0:1.16.2-5.el8_8.6 |
| `python3-unbound-debuginfo` | Red Hat:rhel_e4s:8.8::appstream | All versions | 0:1.16.2-5.el8_8.6 |
| `unbound` | Red Hat:rhel_e4s:8.8::appstream | All versions | 0:1.16.2-5.el8_8.6 |
| `unbound-debuginfo` | Red Hat:rhel_e4s:8.8::appstream | All versions | 0:1.16.2-5.el8_8.6 |
| `unbound-debugsource` | Red Hat:rhel_e4s:8.8::appstream | All versions | 0:1.16.2-5.el8_8.6 |
| `unbound-devel` | Red Hat:rhel_e4s:8.8::appstream | All versions | 0:1.16.2-5.el8_8.6 |
| `unbound-libs` | Red Hat:rhel_e4s:8.8::appstream | All versions | 0:1.16.2-5.el8_8.6 |
| `unbound-libs-debuginfo` | Red Hat:rhel_e4s:8.8::appstream | All versions | 0:1.16.2-5.el8_8.6 |
| `python3-unbound` | Red Hat:rhel_e4s:9.2::appstream | All versions | 0:1.16.2-3.el9_2.6 |
| `python3-unbound-debuginfo` | Red Hat:rhel_e4s:9.2::appstream | All versions | 0:1.16.2-3.el9_2.6 |
| `unbound` | Red Hat:rhel_e4s:9.2::appstream | All versions | 0:1.16.2-3.el9_2.6 |
| `unbound-debuginfo` | Red Hat:rhel_e4s:9.2::appstream | All versions | 0:1.16.2-3.el9_2.6 |
| `unbound-debugsource` | Red Hat:rhel_e4s:9.2::appstream | All versions | 0:1.16.2-3.el9_2.6 |
| `unbound-libs` | Red Hat:rhel_e4s:9.2::appstream | All versions | 0:1.16.2-3.el9_2.6 |
| `unbound-libs-debuginfo` | Red Hat:rhel_e4s:9.2::appstream | All versions | 0:1.16.2-3.el9_2.6 |
| `python3-unbound` | Red Hat:rhel_e4s:9.4::appstream | All versions | 0:1.16.2-8.el9_4.3 |
| `python3-unbound-debuginfo` | Red Hat:rhel_e4s:9.4::appstream | All versions | 0:1.16.2-8.el9_4.3 |
| `unbound` | Red Hat:rhel_e4s:9.4::appstream | All versions | 0:1.16.2-8.el9_4.3 |
| `unbound-debuginfo` | Red Hat:rhel_e4s:9.4::appstream | All versions | 0:1.16.2-8.el9_4.3 |
| `unbound-debugsource` | Red Hat:rhel_e4s:9.4::appstream | All versions | 0:1.16.2-8.el9_4.3 |
| `unbound-libs` | Red Hat:rhel_e4s:9.4::appstream | All versions | 0:1.16.2-8.el9_4.3 |
| `unbound-libs-debuginfo` | Red Hat:rhel_e4s:9.4::appstream | All versions | 0:1.16.2-8.el9_4.3 |
| `unbound` | Red Hat:rhel_els:7 | All versions | 0:1.6.6-5.el7_9.2 |
| `unbound-debuginfo` | Red Hat:rhel_els:7 | All versions | 0:1.6.6-5.el7_9.2 |
| `unbound-devel` | Red Hat:rhel_els:7 | All versions | 0:1.6.6-5.el7_9.2 |
| `unbound-libs` | Red Hat:rhel_els:7 | All versions | 0:1.6.6-5.el7_9.2 |
| `unbound-python` | Red Hat:rhel_els:7 | All versions | 0:1.6.6-5.el7_9.2 |
| `unbound` | Red Hat:rhel_eus:9.6::appstream | All versions | 0:1.16.2-19.el9_6.2 |
| `unbound-libs` | Red Hat:rhel_eus:9.6::appstream | All versions | 0:1.16.2-19.el9_6.2 |
| `unbound` | Red Hat:rhel_eus_long_life:8.4::appstream | All versions | 0:1.7.3-15.el8_4.4 |
| `unbound-libs` | Red Hat:rhel_eus_long_life:8.4::appstream | All versions | 0:1.7.3-15.el8_4.4 |
| `unbound` | Red Hat:rhel_eus_long_life:8.6::appstream | All versions | 0:1.7.3-17.el8_6.8 |
| `unbound-libs` | Red Hat:rhel_eus_long_life:8.6::appstream | All versions | 0:1.7.3-17.el8_6.8 |
| `python3-unbound` | Red Hat:rhel_tus:8.8::appstream | All versions | 0:1.16.2-5.el8_8.6 |

Products: Nlnetlabs Unbound.

## How do I fix CVE-2026-81642?

Upgrade to a fixed version.

## Is CVE-2026-81642 being exploited?

There is no known exploitation of CVE-2026-81642 in the wild and no public exploit code.

Public exploit code:

- Tracking the Unbound CVE-2026-81642 DNSKEY digest heap overflow (github_poc): https://github.com/suominen/CVE-2026-81642

## Other vulnerabilities in Nlnetlabs Unbound

- [CVE-2026-33278](https://insights.sbomify.com/CVE-2026-33278/): Possible arbitrary code execution during DNSSEC validation (critical 9.1)
- [CVE-2026-42944](https://insights.sbomify.com/CVE-2026-42944/): Heap overflow with multiple NSID, COOKIE, PADDING EDNS options (high 8.7)
- [CVE-2026-42959](https://insights.sbomify.com/CVE-2026-42959/): Crash during DNSSEC validation of malicious content (high 8.7)
- [CVE-2026-82717](https://insights.sbomify.com/CVE-2026-82717/): CNAME synthesis could lead to heap corruption (high 8.4)
- [CVE-2026-81634](https://insights.sbomify.com/CVE-2026-81634/): Possible heap buffer overflow during DNSSEC canonicalization (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-81642 and fix it if it is affected.

What it is: CVE-2026-81642 is a critical memory corruption vulnerability in Nlnetlabs Unbound, published on 16 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-81642 in the wild and no public exploit code.

Affected product: Nlnetlabs Unbound. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-81642/ (Markdown: https://insights.sbomify.com/CVE-2026-81642/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-81642
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-81642
- OSV: https://osv.dev/vulnerability/CVE-2026-81642

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-81642/
Summaries are generated and may contain mistakes; the official description above is the record.