rsync 2.0.0 < 3.5.0 Connection Slot Exhaustion DoS via Handshake Stall
RsyncProject · rsync
8.7HighCVSS 4.0
Recommended action
Within 7 days
High technical severity; prioritise exposed affected systems while verifying vendor guidance.
Patch available
Distribution package intelligence
Ubuntu vendor package status
Canonical’s release and source-package findings are shown separately from local repository availability.
1 package state
Repository candidate not checked
A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.
Ubuntu release
Source package
Vendor state
Fixed version
Evidence
Ubuntu 24.04 LTSnoble · standard archive
rsync
Under evaluationCanonical reports that the package might be affected and still needs evaluation or fixing.
Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.
1 current
CVE-2026-70464 · CSAF 2.0 · revision 3 · finalRed Hat Product Securityrsync: rsync: Denial of Service via handshake stall
17 known affected
The vendor explicitly identifies these products as affected by this CVE.
rsync as a component of Red Hat Enterprise Linux 10
rsync-daemon as a component of Red Hat Enterprise Linux 10
rsync-rrsync as a component of Red Hat Enterprise Linux 10
rsync.src as a component of Red Hat Enterprise Linux 10
rsync as a component of Red Hat Enterprise Linux 6
rsync.src as a component of Red Hat Enterprise Linux 6
rsync as a component of Red Hat Enterprise Linux 7
rsync.src as a component of Red Hat Enterprise Linux 7
rsync as a component of Red Hat Enterprise Linux 8
rsync-daemon as a component of Red Hat Enterprise Linux 8
rsync.src as a component of Red Hat Enterprise Linux 8
rsync as a component of Red Hat Enterprise Linux 9
Summary
A denial of service flaw was found in the rsync daemon. An unauthenticated remote attacker can stall the handshake process by opening multiple concurrent connections and trickling data or stalling prior to module selection. This bypasses standard timeouts and exhausts all available connection slots, preventing legitimate clients from connecting.
Remediation
Disable the rsync daemon if unused (systemctl disable --now rsyncd), or strictly restrict TCP/873 access to trusted clients using firewall rules and hosts allow directives. Do not rely on standard module timeout settings, as they do not protect against this specific pre-handshake stall. While configuring system limits (TasksMax/LimitNOFILE) can prevent full host resource exhaustion, aggressive IP-based connection filtering is the only reliable way to keep the targeted rsync module available.
Optional official sources
National CERT insights ?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.
Select the national-authority views to include. The exact source language is shown on each matched advisory. Your choice is remembered on this device and encoded in the shareable URL.
Official European source
ENISA European Vulnerability Database
Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.
1 current
ENISA EUVD identifier
EUVD-2026-58040
No EUVD known-exploited evidence
ENISA has published the identifier mapping but no EUVD description has been stored yet.
EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
Not supplied in the stored EUVD record
Advisory evidence
No linked advisory details stored yet
Recommended actionWithin 7 days
High technical severity; prioritise exposed affected systems while verifying vendor guidance.
Patch available
01
What, why and how
rsync daemon 2.0.0 before 3.5.0 contains a denial of service vulnerability that allows unauthenticated remote attackers to exhaust daemon connection slots by stalling the handshake process before or after module selection without triggering the I/O timeout. Attackers can open many simultaneous connections and trickle data at the minimum rate to avoid timeout, or stall entirely before module selection where no timeout applies, consuming all available connection slots and denying service to legitimate clients.
What
rsync daemon 2.0.0 before 3.5.0 contains a denial of service vulnerability that allows unauthenticated remote attackers to exhaust daemon connection slots by stalling the handshake process before or after module selection without triggering the I/O timeout. Attackers can open many simultaneous connections and trickle data at the minimum rate to avoid timeout, or stall entirely before module selection where no timeout applies, consuming all available connection slots and denying service to legitimate clients.
Why
The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.
How
An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may disrupt the affected service.
What
rsync daemon 2.0.0 before 3.5.0 contains a denial of service vulnerability that allows unauthenticated remote attackers to exhaust daemon connection slots by stalling the handshake process before or after module selection without triggering the I/O timeout. Attackers can open many simultaneous connections and trickle data at the minimum rate to avoid timeout, or stall entirely before module selection where no timeout applies, consuming all available connection slots and denying service to legitimate clients.
Why
The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.
How
An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may disrupt the affected service.
02
Exploit reality and attack path
CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.
Observed exploitation ?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.No confirmed evidence
No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.
Public PoC / exploit material ?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.None recorded
No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.
Likely attack path
a network path → Allocation of Resources Without Limits or Throttling → disrupt the affected service
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Not a CVSS 4.0 base metric
Weakness ?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-770: Allocation of Resources Without Limits or Throttling. The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.
CVSS vector ?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
Common Vulnerability Scoring System 4.0: the compact vector below is decoded into plain language.
AVNetworkAttack vector: The vulnerable component can be reached over a network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.ATNoneAttack requirements: No additional deployment or execution condition is required.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.VCNoneVulnerable-system confidentiality: No direct loss is represented by this metric.VINoneVulnerable-system integrity: No direct loss is represented by this metric.VAHighVulnerable-system availability: A successful attack can cause a major loss.SCNoneSubsequent-system confidentiality: No direct loss is represented by this metric.SINoneSubsequent-system integrity: No direct loss is represented by this metric.SANoneSubsequent-system availability: No direct loss is represented by this metric.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
NetworkUnauthenticatedDenial of serviceCWE-770
A
Official authority intelligence
Only matched European and national findings are included. Language selectors and unavailable sources are omitted.
ENISA EUVD · EUVD-2026-58040Official EUVD mapping
0 linked advisory records.
Official EUVD recordBSI · German · WID-SEC-W-2026-2817Rsync: Mehrere Schwachstellen
Ein Angreifer kann mehrere Schwachstellen in Rsync ausnutzen, um seine Privilegien zu erhöhen, beliebigen Code auszuführen, Daten offenzulegen oder zu manipulieren, Sicherheitsmaßnahmen zu umgehen oder Denial-of-Service-Zustände herbeizuführen.
Official advisoryCSIRT Italia · Italian · rilevate-vulnerabilita-in-rsync-1Rilevate vulnerabilità in Rsync
Rilevate 19 vulnerabilità, di cui 5 con gravità “critica” e 14 con gravità "alta", in Rsync, software open source per la sincronizzazione e il trasferimento di file tra sistemi.
Operational remediation based on structured source evidence.
Status ?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Patch available
Affected
rsync as a component of Red Hat Enterprise Linux 10; rsync-daemon as a component of Red Hat Enterprise Linux 10; rsync-rrsync as a component of Red Hat Enterprise Linux 10; rsync.src as a component of Red Hat Enterprise Linux 10; rsync as a component of Red Hat Enterprise Linux 6; rsync.src as a component of Red Hat Enterprise Linux 6; rsync as a component of Red Hat Enterprise Linux 7; rsync.src as a component of Red Hat Enterprise Linux 7; rsync as a component of Red Hat Enterprise Linux 8; rsync-daemon as a component of Red Hat Enterprise Linux 8; rsync.src as a component of Red Hat Enterprise Linux 8; rsync as a component of Red Hat Enterprise Linux 9; rsync-daemon as a component of Red Hat Enterprise Linux 9; rsync-rrsync as a component of Red Hat Enterprise Linux 9; rsync.src as a component of Red Hat Enterprise Linux 9; openshift/ose-rhel-coreos-8 as a component of Red Hat OpenShift Container Platform 4; openshift/ose-rhel-coreos-9 as a component of Red Hat OpenShift Container Platform 4
Fixed
3.5.0
Action
Review the linked authoritative reference and apply the recorded fixed release appropriate to the affected product branch.
Workaround
Disable the rsync daemon if unused (systemctl disable --now rsyncd), or strictly restrict TCP/873 access to trusted clients using firewall rules and hosts allow directives. Do not rely on standard module timeout settings, as they do not protect against this specific pre-handshake stall. While configuring system limits (TasksMax/LimitNOFILE) can prevent full host resource exhaustion, aggressive IP-based connection filtering is the only reliable way to keep the targeted rsync module available.
04
Evidence and provenance
Published 13 Aug 2026 · Last source change 14 Aug 2026, 16:51 UTC · CWE-770 · Allocation of Resources Without Limits or Throttling
CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source ?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2026-58040
Product sourceVendor CSAF · Red Hat Product Security
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceCNA
NVD statusNVD awaiting enrichment
Core structured fields are present and their contributing authorities are shown above.
Affected versionsThe structured affected or fixed version information changed.
Before
rsync as a component of Red Hat Enterprise Linux 10; rsync-daemon as a component of Red Hat Enterprise Linux 10; rsync-rrsync as a component of Red Hat Enterprise Linux 10; rsync.src as a component of Red Hat Enterprise Linux 10; rsync as a component of Red Hat Enterprise Linux 6; rsync.src as a component of Red Hat Enterprise Linux 6; rsync as a component of Red Hat Enterprise Linux 7; rsync.src as a component of Red Hat Enterprise Linux 7; rsync as a component of Red Hat Enterprise Linux 8; rsync-daemon as a component of Red Hat Enterprise Linux 8; rsync.src as a component of Red Hat Enterprise Linux 8; rsync as a component of Red Hat Enterprise Linux 9; rsync-daemon as a component of Red Hat Enterprise Linux 9; rsync-rrsync as a component of Red Hat Enterprise Linux 9; rsync.src as a component of Red Hat Enterprise Linux 9; openshift/ose-rhel-coreos-9 as a component of Red Hat OpenShift Container Platform 4
After
rsync as a component of Red Hat Enterprise Linux 10; rsync-daemon as a component of Red Hat Enterprise Linux 10; rsync-rrsync as a component of Red Hat Enterprise Linux 10; rsync.src as a component of Red Hat Enterprise Linux 10; rsync as a component of Red Hat Enterprise Linux 6; rsync.src as a component of Red Hat Enterprise Linux 6; rsync as a component of Red Hat Enterprise Linux 7; rsync.src as a component of Red Hat Enterprise Linux 7; rsync as a component of Red Hat Enterprise Linux 8; rsync-daemon as a component of Red Hat Enterprise Linux 8; rsync.src as a component of Red Hat Enterprise Linux 8; rsync as a component of Red Hat Enterprise Linux 9; rsync-daemon as a component of Red Hat Enterprise Linux 9; rsync-rrsync as a component of Red Hat Enterprise Linux 9; rsync.src as a component of Red Hat Enterprise Linux 9; openshift/ose-rhel-coreos-8 as a component of Red Hat OpenShift Container Platform 4; openshift/ose-rhel-coreos-9 as a component of Red Hat OpenShift Container Platform 4
Affected versionsThe structured affected or fixed version information changed.
Before
rsync as a component of Red Hat Enterprise Linux 10; rsync-daemon as a component of Red Hat Enterprise Linux 10; rsync-rrsync as a component of Red Hat Enterprise Linux 10; rsync.src as a component of Red Hat Enterprise Linux 10; rsync as a component of Red Hat Enterprise Linux 6; rsync.src as a component of Red Hat Enterprise Linux 6; rsync as a component of Red Hat Enterprise Linux 7; rsync.src as a component of Red Hat Enterprise Linux 7; rsync as a component of Red Hat Enterprise Linux 8; rsync-daemon as a component of Red Hat Enterprise Linux 8; rsync.src as a component of Red Hat Enterprise Linux 8; rsync as a component of Red Hat Enterprise Linux 9; rsync-daemon as a component of Red Hat Enterprise Linux 9; rsync-rrsync as a component of Red Hat Enterprise Linux 9; rsync.src as a component of Red Hat Enterprise Linux 9; rhcos as a component of Red Hat OpenShift Container Platform 4
After
rsync as a component of Red Hat Enterprise Linux 10; rsync-daemon as a component of Red Hat Enterprise Linux 10; rsync-rrsync as a component of Red Hat Enterprise Linux 10; rsync.src as a component of Red Hat Enterprise Linux 10; rsync as a component of Red Hat Enterprise Linux 6; rsync.src as a component of Red Hat Enterprise Linux 6; rsync as a component of Red Hat Enterprise Linux 7; rsync.src as a component of Red Hat Enterprise Linux 7; rsync as a component of Red Hat Enterprise Linux 8; rsync-daemon as a component of Red Hat Enterprise Linux 8; rsync.src as a component of Red Hat Enterprise Linux 8; rsync as a component of Red Hat Enterprise Linux 9; rsync-daemon as a component of Red Hat Enterprise Linux 9; rsync-rrsync as a component of Red Hat Enterprise Linux 9; rsync.src as a component of Red Hat Enterprise Linux 9; openshift/ose-rhel-coreos-9 as a component of Red Hat OpenShift Container Platform 4
Affected versionsThe structured affected or fixed version information changed.
Before
After
rsync as a component of Red Hat Enterprise Linux 10; rsync-daemon as a component of Red Hat Enterprise Linux 10; rsync-rrsync as a component of Red Hat Enterprise Linux 10; rsync.src as a component of Red Hat Enterprise Linux 10; rsync as a component of Red Hat Enterprise Linux 6; rsync.src as a component of Red Hat Enterprise Linux 6; rsync as a component of Red Hat Enterprise Linux 7; rsync.src as a component of Red Hat Enterprise Linux 7; rsync as a component of Red Hat Enterprise Linux 8; rsync-daemon as a component of Red Hat Enterprise Linux 8; rsync.src as a component of Red Hat Enterprise Linux 8; rsync as a component of Red Hat Enterprise Linux 9; rsync-daemon as a component of Red Hat Enterprise Linux 9; rsync-rrsync as a component of Red Hat Enterprise Linux 9; rsync.src as a component of Red Hat Enterprise Linux 9; rhcos as a component of Red Hat OpenShift Container Platform 4
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
CVE-2026-70464: rsync 2.0.0 < 3.5.0 Connection Slot Exhaustion DoS via Handshake Stall | BlackTree
