# CVE-2026-70455: rsync 3.4.2 < 3.5.0 DoS via --zt Zstandard Compression Thread Exhaustion

CVE-2026-70455 is fixed in 3 products on 1 platform, first by RHSA-2026:67463, released August 13, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-70455
- Priority: High
- CVSS: 8.2 (Important)
- EPSS: 0.0057
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Aug 13, 2026
- Weakness: Allocation of Resources Without Limits or Throttling
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-70455

## Description

rsync 3.4.2 before 3.5.0 contains a denial of service vulnerability that allows a remote sender to exhaust system resources by specifying the --zt short alias for --compress-threads, which bypasses the refuse options directive's string matching on long option names. Attackers can specify --zt=N with a large value to spawn an unbounded number of Zstandard worker threads on the receiver, exhausting available thread and memory resources.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | rsync Debian 13.5 (trixie) | 3.5.0+ds1-0+deb13u1 | [DEBIAN-CVE-2026-70455](https://patchblox.com/security/data/fix/linux/debian-cve-2026-70455.md) | Aug 27, 2026 |
| Linux | rsync Debian 14 | 3.5.0+ds1-1 | [DEBIAN-CVE-2026-70455](https://patchblox.com/security/data/fix/linux/debian-cve-2026-70455.md) | Aug 27, 2026 |
| Linux | rsync RHEL 10 | 3.5.0-3.el10_2 | [RHSA-2026:67463](https://patchblox.com/security/data/fix/linux/rhsa-2026-67463.md) | Aug 13, 2026 |
| Linux | rsync almalinux 10 | 3.5.0-3.el10_2 | [ALSA-2026:67463](https://patchblox.com/security/data/fix/linux/alsa-2026-67463.md) | Sep 14, 2026 |
| Linux | rsync ol 10 | 0:3.5.0-3.el10_2 | [ELSA-2026-67463-0](https://patchblox.com/security/data/fix/linux/elsa-2026-67463-0.md) | Sep 16, 2026 |
| Linux | rsync opensuse-leap 16.0 | 3.4.1-160000.6.1 | [OPENSUSE-SU-2026:21650-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21650-1.md) | Aug 26, 2026 |
| Linux | rsync rocky 10 | 0:3.5.0-3.el10_2 | [RLSA-2026:67463](https://patchblox.com/security/data/fix/linux/rlsa-2026-67463.md) | Sep 15, 2026 |
| Linux | rsync sles 15.6 | 3.2.7-150600.3.24.1 | [SUSE-SU-2026:3657-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-3657-1.md) | Aug 20, 2026 |
| Linux | rsync sles 15.7 | 3.2.7-150600.3.24.1 | [SUSE-SU-2026:3657-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-3657-1.md) | Aug 20, 2026 |
| Linux | rsync sles 16.0 | 3.4.1-160000.6.1 | [SUSE-SU-2026:23323-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-23323-1.md) | Aug 26, 2026 |
| Linux | rsync-daemon almalinux 10 | 3.5.0-3.el10_2 | [ALSA-2026:67463](https://patchblox.com/security/data/fix/linux/alsa-2026-67463.md) | Sep 14, 2026 |
| Linux | rsync-daemon ol 10 | 0:3.5.0-3.el10_2 | [ELSA-2026-67463-0](https://patchblox.com/security/data/fix/linux/elsa-2026-67463-0.md) | Sep 16, 2026 |
| Linux | rsync-rrsync almalinux 10 | 3.5.0-3.el10_2 | [ALSA-2026:67463](https://patchblox.com/security/data/fix/linux/alsa-2026-67463.md) | Sep 14, 2026 |
| Linux | rsync-rrsync ol 10 | 0:3.5.0-3.el10_2 | [ELSA-2026-67463-0](https://patchblox.com/security/data/fix/linux/elsa-2026-67463-0.md) | Sep 16, 2026 |

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Data as of 2026-11-08T19:12:23Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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