CVE-2021-31875

CRITICAL

Cesanta MongooseOS mJS 1.26 - Heap-Based Buffer Overflow via Malformed JSON String

Title source: llm
STIX 2.1

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."

References (3)

Core 3
Core References
Patch, Third Party Advisory
https://github.com/418sec/mjs/pull/2
Release Notes, Third Party Advisory
https://github.com/cesanta/mjs/releases/tag/1.26
Exploit, Third Party Advisory
https://huntr.dev/bounties/1-other-mjs/

Scores

CVSS v3 9.8
EPSS 0.0217
EPSS Percentile 79.9%
Attack Vector NETWORK
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Details

CWE
CWE-193 CWE-787
Status published
Products (1)
cesanta/mongooseos_mjs 1.26
Published Apr 29, 2021
Tracked Since Feb 18, 2026