CVE-2021-31875

Name: CVE-2021-31875
Creator: NVD / NIST
Published: 2021-04-29T02:15:08.043+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

CRITICALCVSS 9.8/10EPSS 2.17%

Last modified Jun 17, 2026

CVE-2021-31875 is a critical-severity vulnerability rated 9.8/10 on the CVSS scale. In mjs_json.c in Cesanta MongooseOS mJS 1.26, a maliciously formed JSON string can trigger an off-by-one heap-based buffer overflow in mjs_json_parse, which can potentially lead to redirection of control flow. NOTE: the original reporter disputes the significance of this finding because "there isn’t very much of an opportunity to exploit this reliably for an information leak, so there isn’t any real security impact.". EPSS estimates a 2.17% chance of exploitation in the next 30 days.

Description

In mjs_json.c in Cesanta MongooseOS mJS 1.26, a maliciously formed JSON string can trigger an off-by-one heap-based buffer overflow in mjs_json_parse, which can potentially lead to redirection of control flow. NOTE: the original reporter disputes the significance of this finding because "there isn’t very much of an opportunity to exploit this reliably for an information leak, so there isn’t any real security impact."

Metrics

CVSS 3.1

9.8/10

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

EPSS Probability

2.17%

80.0th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Cesanta	Mongooseos Mjs	1.26

References

https://github.com/418sec/mjs/pull/2Patch, Third Party Advisory
https://github.com/cesanta/mjs/releases/tag/1.26Release Notes, Third Party Advisory
https://huntr.dev/bounties/1-other-mjs/Exploit, Third Party Advisory
https://github.com/418sec/mjs/pull/2Patch, Third Party Advisory
https://github.com/cesanta/mjs/releases/tag/1.26Release Notes, Third Party Advisory
https://huntr.dev/bounties/1-other-mjs/Exploit, Third Party Advisory

Timeline

Published: Apr 29, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-31875?

How severe is CVE-2021-31875?

CVE-2021-31875 has a CVSS score of 9.8/10 (CRITICAL severity). The EPSS model estimates a 2.17% probability of exploitation in the next 30 days.

How do I fix CVE-2021-31875?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-31875?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST