Rsync < 3.4.3 TOCTOU Race Condition Allows Symlink-Based Arbitrary File Write
Summary
| CVE | CVE-2026-29518 |
|---|---|
| State | PUBLISHED |
| Assigner | VulnCheck |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-05-20 13:16:17 UTC |
| Updated | 2026-06-30 03:18:08 UTC |
| Description | 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. |
Risk And Classification
Primary CVSS: v4.0 7.3 HIGH from [email protected]
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/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
EPSS: 0.001520000 probability, percentile 0.047390000 (date 2026-07-04)
Problem Types: CWE-367 | CWE-367 Time-of-check Time-of-use (TOCTOU) Race Condition
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 4.0 | [email protected] | Secondary | 7.3 | HIGH | 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/E:X/C... |
| 4.0 | CNA | CVSS | 7.3 | HIGH | 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 |
| 3.1 | ADP | CVSS | 7.8 | HIGH | CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H |
| 3.1 | [email protected] | Primary | 7 | HIGH | CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H |
| 3.1 | 0b0ca135-0b70-47e7-9f44-1890c2a1c46c | Secondary | 7.8 | HIGH | CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H |
| 3.1 | CNA | CVSS | 7 | HIGH | CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H |
CVSS v4.0 Breakdown
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/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
CVSS v3.1 Breakdown
CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H
NVD Known Affected Configurations (CPE 2.3)
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | RsyncProject | Rsync | affected 3.4.3 semver | Not specified |
| ADP | Red Hat | Red Hat Enterprise Linux AppStream V. 10 | Not specified | Not specified |
| ADP | Red Hat | Red Hat Enterprise Linux AppStream V. 9 | Not specified | Not specified |
| ADP | Red Hat | Red Hat Enterprise Linux BaseOS V. 10 | Not specified | Not specified |
| ADP | Red Hat | Red Hat Enterprise Linux BaseOS V. 8 | Not specified | Not specified |
| ADP | Red Hat | Red Hat Enterprise Linux BaseOS V. 9 | Not specified | Not specified |
| ADP | Red Hat | Red Hat Discovery 2 | Not specified | Not specified |
| ADP | Red Hat | Red Hat Enterprise Linux 6 | Not specified | Not specified |
| ADP | Red Hat | Red Hat Enterprise Linux 7 | Not specified | Not specified |
| ADP | Red Hat | Red Hat OpenShift Container Platform 4 | Not specified | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-29518.json | 0b0ca135-0b70-47e7-9f44-1890c2a1c46c | security.access.redhat.com | |
| access.redhat.com/errata/RHSA-2026:26408 | 0b0ca135-0b70-47e7-9f44-1890c2a1c46c | access.redhat.com | |
| bugzilla.redhat.com/show_bug.cgi | 0b0ca135-0b70-47e7-9f44-1890c2a1c46c | bugzilla.redhat.com | |
| access.redhat.com/errata/RHSA-2026:26410 | 0b0ca135-0b70-47e7-9f44-1890c2a1c46c | access.redhat.com | |
| access.redhat.com/errata/RHSA-2026:26332 | 0b0ca135-0b70-47e7-9f44-1890c2a1c46c | access.redhat.com | |
| github.com/RsyncProject/rsync/pull/895/changes/8471fdd1561049ef5f58df44a... | [email protected] | github.com | Patch |
| www.vulncheck.com/advisories/rsync-toctou-race-condition-allows-symlink-based-a... | [email protected] | www.vulncheck.com | Third Party Advisory |
| access.redhat.com/security/cve/CVE-2026-29518 | 0b0ca135-0b70-47e7-9f44-1890c2a1c46c | access.redhat.com | |
| access.redhat.com/errata/RHSA-2026:29197 | 0b0ca135-0b70-47e7-9f44-1890c2a1c46c | access.redhat.com | |
| github.com/RsyncProject/rsync/releases/tag/v3.4.3 | [email protected] | github.com | Release Notes |
| michael.stapelberg.ch/posts/2026-05-24-minimal-memory-safe-go-rsync-vulns | [email protected] | michael.stapelberg.ch | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
Vendor Comments And Credit
Discovery Credit
CNA: Nullx3D (Batuhan SANCAK) (en)
CNA: Michael Stapelberg (en)
CNA: Damien Neil (en)
Additional Advisory Data
| Source | Time | Event |
|---|---|---|
| ADP | 2026-05-11T13:09:31.417Z | Reported to Red Hat. |
| ADP | 2026-05-20T00:00:00.000Z | Made public. |
Solutions
ADP: RHSA-2026:26332: Red Hat Enterprise Linux AppStream (v. 10), Red Hat Enterprise Linux BaseOS (v. 10)
ADP: RHSA-2026:26410: Red Hat Enterprise Linux AppStream (v. 9), Red Hat Enterprise Linux BaseOS (v. 9)
ADP: RHSA-2026:26408: Red Hat Enterprise Linux BaseOS (v. 8)
ADP: RHSA-2026:29197: Red Hat Discovery 2
Workarounds
ADP: To prevent exploitation, ensure the rsync daemon is configured with `use chroot = yes`. This setting, which is the default, isolates the rsync process and prevents the symlink race condition. If `use chroot = no` is present in the rsync configuration (e.g., `/etc/rsyncd.conf`), it must be changed to `use chroot = yes`. A restart of the rsync service is required for any configuration changes to take effect.