What is CVE-2021-33439?

CVE-2021-33439 is a medium-severity vulnerability in Cesanta Mjs, classified under Integer Overflow or Wraparound. CVSS score: 5.5/10. Published 2022-07-26.

How severe is CVE-2021-33439?

Medium severity. CVSS v3 base score is 5.5 out of 10.

NULL pointer dereference in Cesanta Mjs

CVE-2021-33439

An issue was discovered in mjs (mJS: Restricted JavaScript engine), ES6 (JavaScript version 6). There is Integer overflow in gc_compact_strings() in mjs.c.

Vulnerability class: Integer Overflow

Published 2022-07-26 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 5.5 (Medium). Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.003 (21.6th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 22nd percentile — 21.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.003 · newest: 0.003 · change: 0.000

Affected products

Cesanta Mjs

Weakness classification (CWE)

References

github.com/cesanta/mjs/issues/159 (Exploit, Patch, Third Party Advisory, Issue Tracking)
gist.github.com/Clingto/bb632c0c463f4b2c97e4f65f751c5e6d (Third Party Advisory)

Frequently asked questions

What is CVE-2021-33439?: CVE-2021-33439 is a medium-severity vulnerability in Cesanta Mjs, classified under Integer Overflow or Wraparound. CVSS score: 5.5/10. Published 2022-07-26.
How severe is CVE-2021-33439?: Medium severity. CVSS v3 base score is 5.5 out of 10.