# CVE-2026-44687: Off-by-one error in 'harden-below-nxdomain' logic can shadow a stub/forward zone by a legitimate parent's NXDOMAIN > An off-by-one error in Unbound's harden-below-nxdomain logic allows DNSSEC-signed parent zones to shadow configured stub or forward zones, bypassing intended routing. - **Severity:** Low 3.7 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 22 Jul 2026 - **Updated:** 22 Jul 2026 - **Also known as:** ALPINE-CVE-2026-44687, AZL-92922, DEBIAN-CVE-2026-44687, ECHO-be32-8712-2a19, GHSA-x324-pxwv-r76h, UBUNTU-CVE-2026-44687 ## What is CVE-2026-44687? CVE-2026-44687 is a low-severity vulnerability in Nlnetlabs Unbound, published on 22 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. ### Official description In NLnet Labs Unbound 1.13.2 up to and including 1.25.1, stub or forward zones where the name is below an intermediate labed below a DNSSEC signed zone could be shadowed by the intermediate label's secure NXDOMAIN answer from the parent. This is caused by an off-by-one error in 'harden-below-nxdomain' logic; enabled by default. It effectively bypasses the configuration and the configured stub/forward zone is never contacted. 'harden-below-nxdomain' does an upward DNS cache walk together with a delegation point guard that does not allow NXDOMAIN synthesis above stub/forward zones. The guard tests the domain name but before stripping a label. This results in an iteration where the domain name equals the configured stub/forward zone apex that passes the guard, strips one more label, and probes the cache at the apex's immediate public parent. If that parent has a cached DNSSEC-secure NXDOMAIN, which it will for any private namespace nested two or more labels under a signed public name, the walk returns it and the configured stub/forward upstream is never contacted. This can only be triggered by the query for the intermediate label (between the stub/forward apex and the DNSSEC parent zone). Weakness: CWE-193 (Off-by-one Error) ## Which versions are affected by CVE-2026-44687? It affects 1 product. Products: Nlnetlabs Unbound. ## How do I fix CVE-2026-44687? Upgrade to a fixed version. ## Is CVE-2026-44687 being exploited? There is no known exploitation of CVE-2026-44687 in the wild and no public exploit code. ## Other vulnerabilities in Nlnetlabs Unbound - [CVE-2026-81642](https://insights.sbomify.com/CVE-2026-81642/): Heap buffer overflow and possible Remote Code Execution when digesting DNSKEY (critical 9.1) - [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) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-44687 and fix it if it is affected. What it is: CVE-2026-44687 is a low-severity vulnerability in Nlnetlabs Unbound, published on 22 Jul 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-2026-44687 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-2026-44687/ (Markdown: https://insights.sbomify.com/CVE-2026-44687/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-44687 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-44687 - OSV: https://osv.dev/vulnerability/CVE-2026-44687 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-44687/ Summaries are generated and may contain mistakes; the official description above is the record.