rsync 3.4.2<3.5.0 DDoS via --zt Zstd thread abuse
CVE-2026-70455 Published on August 13, 2026
rsync 3.4.2 < 3.5.0 DoS via --zt Zstandard Compression Thread Exhaustion
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.
Vulnerability Analysis
CVE-2026-70455 can be exploited with network access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity and availability.
Weakness Type
Allocation of Resources Without Limits or Throttling
The software allocates a reusable resource or group of resources on behalf of an actor without imposing any restrictions on the size or number of resources that can be allocated, in violation of the intended security policy for that actor.
Products Associated with CVE-2026-70455
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Affected Versions
RsyncProject rsync:- Version 3.4.2, <= 3.4.4 is affected.
- Version 3.5.0 is unaffected.