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

highCVSS 7.5CVE-2026-70455

CSIRTS triage

vendor: rsync product: rsync Denial of serviceaffected: 3.4.2 < 3.5.0

What: The --zt Zstandard compression option causes thread exhaustion and denial of service on the target system.
Who is affected: rsync versions 3.4.2 through 3.4.x using the --zt compression flag.
Urgency: High severity; thread exhaustion DoS can be triggered remotely with a single malicious transfer.
Action: Upgrade rsync to version 3.5.0 or later or disable the --zt compression option.

AI-assisted analysis generated from the source advisory — verify against the original.

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Details

Source: Microsoft Security Response Center (INTL · vendor-psirt · site)
Severity: high — CVSS 7.5
Published: 2026-08-11
Exploitation: Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-70455

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-704550.48% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 39% of all EPSS-scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-70455	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

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