# CVE-2026-82717: CNAME synthesis could lead to heap corruption

> Remote attackers can trigger heap corruption in Unbound via crafted CNAME responses, potentially causing crashes or remote code execution.

- **Severity:** High 8.4 (`CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/E:U`)
- **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-2026-82717, AZL-101700, DEBIAN-CVE-2026-82717, ECHO-30a9-8f50-cfd9, GHSA-r5xg-xh8m-9q2w, ROOT-OS-DEBIAN-12-CVE-2026-82717, UBUNTU-CVE-2026-82717

## What is CVE-2026-82717?

CVE-2026-82717 is a high-severity 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 that can progressively corrupt heap memory and under certain systems and compilation options could lead to remote code execution. The vulnerability starts when CNAME synthesis during an upstream response needs to enforce(rewrite) a max TTL value in the packet buffer. Coupled with a compression pointer that points to the overwritten value and invalidates the domain name, it leads to an error path that does not properly move the buffer position and allows for the heap buffer overflow. Since this is heavily reliant on heap memory layout, results are memory corruption that eventually leads to a crash and under specific systems and compilation options remote code execution.

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

## Which versions are affected by CVE-2026-82717?

It affects 1 product.


Products: Nlnetlabs Unbound.

## How do I fix CVE-2026-82717?

Upgrade to a fixed version.

## Is CVE-2026-82717 being exploited?

There is no known exploitation of CVE-2026-82717 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-2026-81634](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-2026-82717 and fix it if it is affected.

What it is: CVE-2026-82717 is a high-severity 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-2026-82717 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-2026-82717/ (Markdown: https://insights.sbomify.com/CVE-2026-82717/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-82717
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-82717
- OSV: https://osv.dev/vulnerability/CVE-2026-82717

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-82717/
Summaries are generated and may contain mistakes; the official description above is the record.