LiveActive security incident?Get immediate response
CVE Record

CVE-2026-29518: Rsync < 3.4.3 TOCTOU Race Condition Allows Symlink-Based Arbitrary File Write

Rsync versions before 3.4.3 contain a time-of-check to time-of-use (TOCTOU) race condition in daemon file handling that allows attackers to redirect file writes outside intended directories by replacing parent directory components with symbolic links. Attackers with write access to a module path can exploit this race condition to create or overwrite arbitrary files, potentially modifying sensitive system files and achieving privilege escalation when the daemon runs with elevated privileges. This vulnerability can only be triggered if the chroot setting is false.

HighCVSS 7.8Not KEV-listedUpdated
Discuss exposureBack to CVEs
Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A user able to write into a vulnerable rsync daemon module may race the server into writing outside that module. Sensitive system files could be overwritten, potentially causing full system compromise when rsync has elevated privileges. Exposure requires rsync before 3.4.3 and chroot disabled.

Executive priority

Prioritize remediation for privileged rsync daemons with writable, non-chrooted modules. These systems present the clearest path to sensitive-file modification and privilege escalation. Other deployments should still be inventoried promptly, but the required access and race complexity reduce immediate mass-exploitation likelihood.

Technical view

Before rsync 3.4.3, daemon file handling contains a CWE-367 time-of-check/time-of-use race. An attacker with module-path write access can replace a checked parent directory with a symbolic link before use, redirecting writes outside the intended tree. Exploitation has high timing complexity but can affect confidentiality, integrity, and availability across a security boundary.

Likely exposure

Likely exposure is limited to rsync daemon deployments before 3.4.3 where chroot is false and an attacker can write within a module path. Risk rises substantially when the daemon runs with privileges permitting writes to sensitive files. Distribution backports may affect version-based conclusions.

Exploitation context

The source bundle does not establish active exploitation, and the CVE is not marked as KEV. Exploitation requires existing write access and winning a race, consistent with local attack vector, low privileges, and high complexity. Successful exploitation could overwrite arbitrary files and enable privilege escalation.

Researcher notes

The structured affected entry lists version "0" with default status unaffected, conflicting with the narrative scope of versions before 3.4.3. Treat precise product applicability as incomplete until confirmed through rsync or distribution advisories. The central security boundary is parent-component validation followed by later file use.

Mitigation direction

  • Upgrade rsync to 3.4.3 or a vendor-supplied package containing the fix.
  • Until patched, enable chroot for writable daemon modules where operationally safe.
  • Remove unnecessary module write permissions and avoid running the daemon with elevated privileges.
  • Review distribution advisories for backported fixes before judging exposure by version alone.

Validation and detection

  • Inventory rsync daemon hosts, package versions, and distribution backport status.
  • Identify writable modules and confirm whether each has chroot set to false.
  • Determine which users can write within affected module paths.
  • Check daemon service privileges and access to sensitive files outside module roots.
  • Review logs for unexpected writes or symbolic-link activity near module directories.
Prepared
Confidence
medium
Sources
12

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-367: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

Open ATT&CK lookup
description · low confidence lookup

Privilege behavior lookup

The CVE wording references privilege impact, so privilege escalation and authorization behavior review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.

Open ATT&CK lookup
description · low confidence lookup

File access behavior lookup

The CVE wording references file access or upload behavior, so file telemetry and web shell review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.

Open ATT&CK lookup
cve · low confidence lookup

CVE-2026-29518 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

Open ATT&CK lookup
Vulnerability profileCVE Program record
Severity
High
CVSS
7.8 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

3CVSS vectors
5Timeline events
2ADP providers
13Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: total

CVSS vector scores

3 official scores

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
7.8CVSS 3.1HighCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H1.16redhat-SADP
7.3CVSS 4.0HighCVSS:4.0/AV:L/AC:H/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N——VulnCheck
7CVSS 3.1HighCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H15.9VulnCheck

Vulnerability scoring details

Base CVSS 4.0 score

7.3High
CVSS 4.0 vector shape for CVE-2026-29518Attack VectorAttack ComplexityAttack RequirementsPrivileges RequiredUser InteractionVS ConfidentialityVS IntegrityVS AvailabilitySS ConfidentialitySS IntegritySS Availability

Vector: CVSS:4.0/AV:L/AC:H/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Attack Requirements
NonePresent
Privileges Required
NoneLowHigh
User Interaction
NonePassiveActive
VS Confidentiality
HighLowNone
VS Integrity
HighLowNone
VS Availability
HighLowNone
SS Confidentiality
HighLowNone
SS Integrity
HighLowNone
SS Availability
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. ADP timelineredhat-SADP

    Reported to Red Hat.

  3. ADP timelineredhat-SADP

    Made public.

  4. CVE publishedCVE Program

    The CVE record was published.

  5. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
other:ssvc
redhat-SADPrsync: TOCTOU symlink race condition allowing local privilege escalation in daemon mode without chroot.
other:Red Hat severity ratingcvssV3_1
  • 2026-05-11T13:09:31.417Z: Reported to Red Hat.
  • 2026-05-20T00:00:00.000Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
RsyncProjectrsync0unaffected
Weakness

CWE details

CWE-367

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-367 · source CWE mapping

Time-of-check Time-of-use (TOCTOU) Race Condition

Time-of-check Time-of-use (TOCTOU) Race Condition represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs