CVE-2026-5958
Description
A Time-of-Check Time-of-Use (TOCTOU) race condition was found in GNU sed. When the -i (in-place) and --follow-symlinks options are used together, sed resolves the symlink but reopens the path for writing. An attacker with write access to the directory containing the symlink can swap it between the check and the open operations. If a privileged user executes sed in this manner on a path influenced by the attacker, it can lead to arbitrary file overwrites and potential privilege escalation.
Statement
This is a Moderate severity flaw in GNU sed that allows for arbitrary file overwrite. The vulnerability is a Time-of-Check Time-of-Use (TOCTOU) race condition in the --follow-symlinks option, enabling an attacker to cause sed -i --follow-symlinks to read attacker-controlled content and write it to an unintended file. Exploitation requires a privileged process to execute sed on a path that an attacker can influence.
Mitigation
To mitigate this vulnerability, avoid using the `sed -i --follow-symlinks` command in privileged contexts or on paths that can be influenced by untrusted users. This flaw specifically affects the `--follow-symlinks` option, which, when used by a privileged process on an attacker-controlled path, can lead to arbitrary file overwrite. Restricting the use of this specific option in sensitive operations can reduce the risk of exploitation.
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 | 6.3 | N/A | N/A |
| Attack Vector | Local | N/A | N/A |
| Attack Complexity | High | N/A | N/A |
| Privileges Required | Low | N/A | N/A |
| User Interaction | None | N/A | N/A |
| Scope | Unchanged | N/A | N/A |
| Confidentiality | None | N/A | N/A |
| Integrity Impact | High | N/A | N/A |
| Availability Impact | High | N/A | N/A |
Vector
Red Hat: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/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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