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CVE-2026-44687 on CTRL-OS 26.05

Aliases: CVE-2026-44687

Packages: unbound

Status: In Progress

Advisory Information

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).

Updates

2026-07-27 19:41 CEST

Metadata changes:

  • Status for package unbound: “In Progress” (6adb4107d901bc4e75e7e4659d2eccdaebe38c21)

2026-07-23 23:53 CEST

Metadata changes:

  • Status for package unbound: “Plausible”

2026-07-23 23:53 CEST

Metadata changes:

  • Status for package unbound: “New”