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

What is CVE-2026-70455?

CVE-2026-70455 is a high-severity denial of service vulnerability in RsyncProject rsync, published on 13 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official 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.

Weakness: CWE-770

Which versions are affected by CVE-2026-70455?

It affects 1 product.

Products include Samba Rsync.

How do I fix CVE-2026-70455?

Upgrade to a fixed version.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2026-70455 being exploited?

There is no known exploitation of CVE-2026-70455 in the wild and no public exploit code.

Other vulnerabilities in RsyncProject rsync

• CVE-2017-15994 Security feature bypass in n/a Critical 9.8
• CVE-2026-53791 rsync < 3.5.0 Daemon IP Spoofing via PROXY Protocol Header Critical 9.1
• CVE-2026-70461 rsync 3.2.5 < 3.5.0 Heap Out-of-Bounds Write via files-from Entry High 8.8
• CVE-2026-70463 rsync 3.1.0 < 3.5.0 Authorization Bypass via auth users Directive Parsing High 8.6
• CVE-2026-53803 rsync < 3.5.0 Symlink Following Arbitrary File Overwrite High 8.5

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as ALPINE-CVE-2026-70455, AZL-95807, BELL-CVE-2026-70455, DEBIAN-CVE-2026-70455, ECHO-984f-9a90-ebe1, GHSA-rjvj-qgqg-cvx9 and 2 more.