Vulnerabilities > CVE-2020-8833 - Time-of-check Time-of-use (TOCTOU) Race Condition vulnerability in multiple products
Attack vector
LOCAL Attack complexity
HIGH Privileges required
LOW Confidentiality impact
HIGH Integrity impact
NONE Availability impact
NONE Summary
Time-of-check Time-of-use Race Condition vulnerability on crash report ownership change in Apport allows for a possible privilege escalation opportunity. If fs.protected_symlinks is disabled, this can be exploited between the os.open and os.chown calls when the Apport cron script clears out crash files of size 0. A symlink with the same name as the deleted file can then be created upon which chown will be called, changing the file owner to root. Fixed in versions 2.20.1-0ubuntu2.23, 2.20.9-0ubuntu7.14, 2.20.11-0ubuntu8.8 and 2.20.11-0ubuntu22.
Vulnerable Configurations
| Part | Description | Count |
|---|---|---|
| OS | 4 | |
| Application | 1 |
Common Weakness Enumeration (CWE)
Common Attack Pattern Enumeration and Classification (CAPEC)
- Leveraging Race Conditions via Symbolic Links This attack leverages the use of symbolic links (Symlinks) in order to write to sensitive files. An attacker can create a Symlink link to a target file not otherwise accessible to her. When the privileged program tries to create a temporary file with the same name as the Symlink link, it will actually write to the target file pointed to by the attackers' Symlink link. If the attacker can insert malicious content in the temporary file she will be writing to the sensitive file by using the Symlink. The race occurs because the system checks if the temporary file exists, then creates the file. The attacker would typically create the Symlink during the interval between the check and the creation of the temporary file.
- Leveraging Time-of-Check and Time-of-Use (TOCTOU) Race Conditions This attack targets a race condition occurring between the time of check (state) for a resource and the time of use of a resource. The typical example is the file access. The attacker can leverage a file access race condition by "running the race", meaning that he would modify the resource between the first time the target program accesses the file and the time the target program uses the file. During that period of time, the attacker could do something such as replace the file and cause an escalation of privilege.
Nessus
| NASL family | Ubuntu Local Security Checks |
| NASL id | UBUNTU_USN-4315-1.NASL |
| description | Maximilien Bourgeteau discovered that the Apport lock file was created with insecure permissions. This could allow a local attacker to escalate their privileges via a symlink attack. (CVE-2020-8831) Maximilien Bourgeteau discovered a race condition in Apport when setting crash report permissions. This could allow a local attacker to read arbitrary files via a symlink attack. (CVE-2020-8833). Note that Tenable Network Security has extracted the preceding description block directly from the Ubuntu security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues. |
| last seen | 2020-05-06 |
| modified | 2020-04-02 |
| plugin id | 135171 |
| published | 2020-04-02 |
| reporter | Ubuntu Security Notice (C) 2020 Canonical, Inc. / NASL script (C) 2020 and is owned by Tenable, Inc. or an Affiliate thereof. |
| source | https://www.tenable.com/plugins/nessus/135171 |
| title | Ubuntu 16.04 LTS / 18.04 LTS / 19.10 : apport vulnerabilities (USN-4315-1) |
| code | |