CVE-2026-70455
Description
A denial-of-service flaw in rsync allows remote attackers to exhaust system memory and CPU. By sending requests using the --zt Zstandard compression alias, an attacker can bypass security directives and spawn an excessive number of worker threads.
Statement
This Important rsync denial-of-service vulnerability allows remote, unauthenticated attackers to exhaust server resources. By using the --zt alias for Zstandard compression, attackers can bypass refuse options to spawn unlimited worker threads and disrupt the service. RHEL 9 and older versions are unaffected.
Mitigation
If the rsync daemon is unused, immediately disable rsyncd.service to eliminate the attack surface. For active deployments, restrict network access (TCP 873) strictly to trusted hosts using firewall rules. Do not rely on refuse options = compress-threads for protection, as the --zt alias bypasses this configuration. Network isolation is the most effective defense.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.5 | N/A | 7.5 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | None | N/A | None |
| Integrity Impact | None | N/A | None |
| Availability Impact | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Resource Consumption (CPU); DoS: Resource Consumption (Memory); DoS: Resource Consumption (Other)
When allocating resources without limits, an attacker could prevent other systems, applications, or processes from accessing the same type of resource. It can be easy for an attacker to consume many resources by rapidly making many requests or causing larger resources to be used than is needed.
Frequently Asked Questions
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