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rsync CVE-2026-70455

| EUVDEUVD-2026-58049 HIGH
Allocation of Resources Without Limits or Throttling (CWE-770)
2026-08-13 VulnCheck
8.7
CVSS 4.0 · Vendor: VulnCheck
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Severity by source

Vendor (VulnCheck) PRIMARY
8.7 HIGH
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
vuln.today AI
7.5 HIGH

Network vector, no privileges or interaction required for anonymous daemons; scope unchanged, pure availability impact with no confidentiality or integrity effect.

3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
SUSE
7.5 HIGH
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Red Hat
7.5 HIGH
qualitative

Primary rating from Vendor (VulnCheck).

CVSS VectorVendor: VulnCheck

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
X

Lifecycle Timeline

3
Source Code Evidence Fetched
Aug 13, 2026 - 15:44 vuln.today
Analysis Generated
Aug 13, 2026 - 15:44 vuln.today
CVE Published
Aug 13, 2026 - 14:45 cve.org
HIGH 8.7

DescriptionCVE.org

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.

AnalysisAI

Denial of service in rsync's receiver process allows a remote, unauthenticated sender to exhaust thread and memory resources by specifying the --zt short alias for --compress-threads, directly bypassing daemon-side refuse options directives that match only against long option names. Affected versions span 3.4.2 through 3.4.x prior to 3.5.0; the bypass is most damaging to operators who explicitly configured refuse options to block --compress-threads, since they believed a mitigation was in place. No public exploit has been identified at time of analysis and no CISA KEV listing exists, but the CVSS 4.0 score of 8.7 accurately reflects low-complexity, unauthenticated network exploitation with high availability impact.

Technical ContextAI

rsync is a widely deployed file synchronization utility that operates either as a standalone daemon (rsyncd) or over SSH. The vulnerability is rooted in CWE-770 (Allocation of Resources Without Limits or Throttling): when --zt=N is passed, the receiver spawns exactly N Zstandard (zstd) compression worker threads without enforcing any ceiling, consuming thread handles and heap memory proportional to N. The rsync daemon's refuse options security directive is designed to let administrators reject client-specified options by name, but its implementation performs string comparison only against full long option names such as --compress-threads, not registered short aliases such as --zt. This is a security control bypass rather than a pure implementation bug: the resource allocation itself is intentional, but the gatekeeping mechanism is incomplete. The CPE string cpe:2.3:a:rsyncproject:rsync:*:*:*:*:*:*:*:* scopes the affected product to the rsyncproject's canonical rsync implementation across all platforms.

RemediationAI

Upgrade rsync to version 3.5.0, designated by the upstream project as a major security release and available at https://github.com/RsyncProject/rsync/releases/tag/v3.5.0. Where immediate upgrade is not feasible, administrators should manually append --zt to the refuse options list in rsyncd.conf as a compensating control; note that this approach requires identifying and blocking every registered short alias for resource-intensive options, and may be incomplete if additional undiscovered aliases exist - it is a partial mitigation, not equivalent to patching. Restricting rsync daemon access to trusted source IP ranges using rsyncd.conf hosts allow directives or an upstream firewall rule is an independent layer that significantly reduces the attack surface, with the trade-off of blocking legitimate clients from unrestricted ranges. Disabling Zstandard compression support at the rsyncd module level, if the deployment does not require zstd, eliminates the thread-spawning vector entirely. The vendor advisory at https://github.com/RsyncProject/rsync/security/advisories/GHSA-rjvj-qgqg-cvx9 and the VulnCheck advisory at https://www.vulncheck.com/advisories/rsync-dos-via-zt-zstandard-compression-thread-exhaustion provide additional operator guidance.

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Vendor StatusVendor

SUSE

Severity: Important
Product Status
SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS Affected
SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS Affected
SUSE Linux Enterprise High Performance Computing 15 SP5-ESPOS Affected
SUSE Linux Enterprise High Performance Computing 15 SP5-LTSS Affected
SUSE Linux Enterprise Micro 5.3 Affected

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CVE-2026-70455 vulnerability details – vuln.today

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