hosts deny access control bypass in rsync on DNS lookup failure (CVE-2026-70452)

rsync's `match_hostname()` function performs a forward DNS lookup of hostname tokens configured in `hosts deny` rules. When the lookup fails, the function returns "no match" - indistinguishable from a genuine non-match - causing the daemon to silently admit connections from hosts explicitly configured to be blocked. This fail-open behavior requires no attacker control over DNS and is triggered by ordinary conditions such as transient resolver failures or a daemon chroot whose directory tree lacks resolver configuration. Affected versions: - >= 3.1.0, <= 3.4.4 We recommend updating to: 3.5.0. CVSS 9.1 · our assessment: act_now Reference: https://github.com/RsyncProject/rsync/security/advisories/GHSA-6692-28cx-wpqq Details: https://vuln.today/cve/CVE-2026-70452