High [CVE-2026-70464] Denial of Service via handshake stall
This high-severity Red Hat Linux advisory covers CVE-2026-70464 affecting Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9, Red Hat Enterprise Linux 6.
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Summary
rsync daemon 2.0.0 before 3.5.0 contains a denial of service vulnerability that allows unauthenticated remote attackers to exhaust daemon connection slots by stalling the handshake process before or after module selection without triggering the I/O timeout.
Attackers can open many simultaneous connections and trickle data at the minimum rate to avoid timeout, or stall entirely before module selection where no timeout applies, consuming all available connection slots and denying service to legitimate clients.
An unauthenticated remote attacker can stall the handshake process by opening multiple concurrent connections and trickling data or stalling prior to module selection. This bypasses standard timeouts and exhausts all available connection slots, preventing legitimate clients from connecting.
An unauthenticated remote attacker can exhaust available connection slots by stalling the handshake process, preventing legitimate clients from connecting. This vulnerability primarily affects systems where the rsync daemon is explicitly enabled and exposed to untrusted networks.
Red Hat severity: Important — CVSS 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H). Weakness: CWE-770.
Affected products named by the advisory: Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 9; Red Hat Enterprise Linux 6; Red Hat Enterprise Linux 7; and 3 more.
- < 2.0.0
- < 3.5.0
Official advisory · high-confidence parse· fetched 12 days ago·verify at source
- 3.5.0
- rsync-0:3.5.0-3.el10_2
- rsync-0:3.2.7-1.el9_8
- RHSA-2026:67463
- RHSA-2026:67462
Official advisory · high-confidence parse· fetched 12 days ago·verify at source
Mitigation checklist
- Disable the rsync daemon if unused (systemctl disable --now rsyncd), or strictly restrict TCP/873 access to trusted clients using firewall rules and hosts allow directives. Do not rely on standard module timeout settings, as they do not protect against this specific pre-handshake stall. While configuring system limits (TasksMax/LimitNOFILE) can prevent full host resource exhaustion, aggressive IP-based connection filtering is the only reliable way to keep the targeted rsync module available.
Official advisory · high-confidence parse· fetched 12 days ago·verify at source
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