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

Is it exploited?

Not on CISA's list. CISA has not added it to the Known Exploited Vulnerabilities catalog as of 29 Oct 2026. If CISA adds it, this page shows it as known exploited.

How likely is exploitation in the next 30 days?

0.8%

EPSS score, percentile 55.9 of all scored records. A probability estimated by FIRST, not a report of exploitation.

How severe?

8.4 High

CVSS v4.0 base score, given by the CNA

What should I do?

This issue is fixed starting with version 1.26.1Solution from the CVE record.

CISA has set no required action, because the vulnerability is not in KEV.

Advisories and patches (1)

Which versions are affected?

Affected

• before 1.26.1

Versions by product

Source: CISA KEV 2026.10.29, as of 29 Oct 2026; FIRST EPSS, as of 29 Oct 2026; CVE List, as of 29 Oct 2026. About the data.

What to do

Solution (from the CVE record)

This issue is fixed starting with version 1.26.1

Advisories and patches

• nlnetlabs.nl (Vendor advisory)

This summary is based on the CVE record as of 29 Oct 2026. Check the vendor's advisory before you act: affected versions and fixes can change.

Affected products and versions

As listed in the CVE record.

Versions not listed are: unaffected.

Source: CVE List, as of 29 Oct 2026. About the data.

About this vulnerability

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 th…

Summary: CVE record, as of 29 Oct 2026.

• CISA has not added CVE-2026-82717 to its Known Exploited Vulnerabilities (KEV) catalog, as of 29 Oct 2026.
• The CVE record was published on 16 Sep 2026.
• The CVE record carries a CVSS v4.0 base score of 8.4 (High), given by its CNA.
• FIRST's EPSS model puts the probability of exploitation in the next 30 days at 0.8% (percentile 55.9), as of 29 Oct 2026. EPSS is a statistical estimate, not a report of exploitation.
• CISA's SSVC assessment in the CVE record: exploitation none, automatable no, technical impact total.
• The credits in the CVE record name Anthropic (Claude) as finder.

Source: CISA KEV 2026.10.29, as of 29 Oct 2026; CVE List, as of 29 Oct 2026; FIRST EPSS, as of 29 Oct 2026. About the data.

Description

CNAME synthesis could lead to heap corruption

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.

Source: CVE List, as of 29 Oct 2026. About the data.

Timeline