CVE-2026-29518
Description
A flaw was found in rsync. An rsync daemon configured with "use chroot = no" is exposed to a time-of-check / time-of-use race on parent path components. A local attacker with write access to a module can replace a parent directory component with a symlink between the receiver's check and its open(), redirecting reads (basis-file disclosure) and writes (file overwrite) outside the module. Under elevated daemon privilege this allows privilege escalation. Default "use chroot = yes" is not exposed. Reach: local attacker on the daemon host, write access to a module path, daemon configured with use chroot = no.
Statement
This flaw, a Time-of-Check Time-of-Use (TOCTOU) race condition, allows a local attacker with write access to an rsync module path to achieve privilege escalation. This vulnerability specifically impacts rsync daemons configured with use chroot = no. Red Hat's default rsync daemon configuration utilizes use chroot = yes, which is not susceptible to this issue.
Mitigation
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.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.8 | N/A | 7.8 |
| Attack Vector | Local | N/A | Local |
| Attack Complexity | High | N/A | High |
| Privileges Required | Low | N/A | Low |
| User Interaction | None | N/A | None |
| Scope | Changed | N/A | Changed |
| Confidentiality | High | N/A | High |
| Integrity Impact | High | N/A | High |
| Availability Impact | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H
cve.org: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H
Understanding the Weakness (CWE)
Integrity,Other
Technical Impact: Alter Execution Logic; Unexpected State
The attacker can gain access to otherwise unauthorized resources.
Integrity,Other
Technical Impact: Modify Application Data; Modify Files or Directories; Modify Memory; Other
Race conditions such as this kind may be employed to gain read or write access to resources which are not normally readable or writable by the user in question.
Integrity,Other
Technical Impact: Other
The resource in question, or other resources (through the corrupted one), may be changed in undesirable ways by a malicious user.
Non-Repudiation
Technical Impact: Hide Activities
If a file or other resource is written in this method, as opposed to in a valid way, logging of the activity may not occur.
Non-Repudiation,Other
Technical Impact: Other
In some cases it may be possible to delete files a malicious user might not otherwise have access to, such as log files.
Other
Technical Impact: Unexpected State
The product may perform invalid actions when the resource is in an unexpected state.
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