What is CVE-2021-39392?

CVE-2021-39392 is a critical-severity vulnerability in Mylittletools Mylittlebackup, classified under Deserialization of Untrusted Data. CVSS score: 9.8/10. Published 2021-09-15.

How severe is CVE-2021-39392?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Deserialization in Mylittletools Mylittlebackup

CVE-2021-39392

The management tool in MyLittleBackup up to and including 1.7 allows remote attackers to execute arbitrary code because machineKey is hardcoded (the same for all customers' installations) in web.config, and can be used to send serialized ASP code.

Vulnerability class: Insecure Deserialization

Published 2021-09-15 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.023 (82.4th percentile), scored 2026-10-08.

Low probability of exploitation in the next 30 days, but still tracked. 82nd percentile — 82.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.023 · newest: 0.023 · change: 0.000

Affected products

Mylittletools Mylittlebackup

Weakness classification (CWE)

CWE-502 — Deserialization of Untrusted Data

References

www.mylittlebackup.com/mlb/zip/mlb_1.7.zip (Broken Link)
gist.github.com/omriinbar/65827626e63f15e3e50557e2d9d61281 (Third Party Advisory)

Frequently asked questions

What is CVE-2021-39392?: CVE-2021-39392 is a critical-severity vulnerability in Mylittletools Mylittlebackup, classified under Deserialization of Untrusted Data. CVSS score: 9.8/10. Published 2021-09-15.
How severe is CVE-2021-39392?: Critical severity. CVSS v3 base score is 9.8 out of 10.