CVE-2021-31875

Severity: critical (CVSS 9.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 2.2% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2021-04-29 · updated 2026-06-17
Weakness: CWE-193

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."

Affected products

Cesanta Mongooseos Mjs: 1.26

References

https://github.com/418sec/mjs/pull/2
https://github.com/cesanta/mjs/releases/tag/1.26
https://huntr.dev/bounties/1-other-mjs/
https://github.com/418sec/mjs/pull/2
https://github.com/cesanta/mjs/releases/tag/1.26
https://huntr.dev/bounties/1-other-mjs/

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