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Vulnerability record · CVE-2020-8833 · published 22 April 2020

CVE-2020-8833: Canonical ubuntu linux toctou race condition vulnerability

Canonical · Ubuntu Linux

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.

4.7 CVSS 3.1 Medium EPSS 0.34% · top 74.4% CWE-367 · TOCTOU race condition
4.7CVSS 3.1 base score, v2 1.9
0.34%EPSS exploitation probability, 30 days
NoNot in CISA KEV
2Affected product versions listed by NVD
6References, 2 tagged exploit
17 Jun 2026Last modified by NVD

Description

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.

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N

Affected products

2 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://bugs.launchpad.net/ubuntu/+source/apport/+bug/1862933 ExploitThird Party Advisory
https://usn.ubuntu.com/4315-1/ Third Party Advisory
https://usn.ubuntu.com/4315-2/ Third Party Advisory
https://bugs.launchpad.net/ubuntu/+source/apport/+bug/1862933 ExploitThird Party Advisory
https://usn.ubuntu.com/4315-1/ Third Party Advisory
https://usn.ubuntu.com/4315-2/ Third Party Advisory

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Source: NIST National Vulnerability Database (record CVE-2020-8833), CISA KEV, FIRST EPSS (scores of 2026-10-05). This page is refreshed as NVD updates the record.