What’s Vulnerable › Vulnerabilities

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

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-08-13 · updated 2026-10-24
• Weakness: CWE-770

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.

Affected products

• RsyncProject rsync: from 3.4.2 before 3.5.0 — fixed in 3.5.0

How to fix

Upgrade to a fixed version: RsyncProject rsync 3.5.0. Check the vendor advisory for mitigations.

References

• https://github.com/RsyncProject/rsync/releases/tag/v3.5.0
• https://github.com/RsyncProject/rsync/security/advisories/GHSA-rjvj-qgqg-cvx9
• https://www.vulncheck.com/advisories/rsync-dos-via-zt-zstandard-compression-thread-exhaustion

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