CVE-2026-27456
Description
A flaw was found in util-linux. When an /etc/fstab entry is configured with the user,loop options, the mount program checks the file path with user permissions but later opens it with root privileges. This creates a brief Time-of-Check-Time-of-Use (TOCTOU) window where an attacker can substitute the intended file with a malicious symbolic link. This allows a local unprivileged user to mount any root-owned file or block device that contains a valid filesystem, gaining full read access to its contents.
Statement
This vulnerability is only exploitable when an /etc/fstab entry exists with user,loop options and its source path points to a directory where the attacker has write permission (e.g., the user's home directory). Also, this issue allows an attacker to mount any root-owned file or block device containing a valid filesystem, causing information disclosure. There is no memory corruption or arbitrary code execution. Due to these reasons, this flaw has been rated with a moderate severity.
Mitigation
To mitigate this flaw, remove the 'user' option from any loop mounts in the /etc/fstab file or ensure the the source path points to a root-owned directory where unprivileged users do not have write permissions.
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 | 4.7 | N/A | 4.7 |
| 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 | Unchanged | N/A | Unchanged |
| Confidentiality | High | N/A | High |
| Integrity Impact | None | N/A | None |
| Availability Impact | None | N/A | None |
Vector
Red Hat: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
cve.org: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
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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