CVE-2021-31875

CRITICAL 9.8CVE-2021-31875 · Published 29/04/2021 · updated 17/06/2026

In short

CVE-2021-31875 is a CRITICAL (CVSS 9.8) vulnerability affecting mongooseos mjs (cesanta).
Chance of exploitation in the next 30 days (EPSS): 2.2%, higher than 82.3% of all vulnerabilities.
No patched version is listed yet: follow the vendor's advisory in References.

Package	Affected versions	Patched versions
mongooseos mjs cesanta	`= 1.26`	No fix yet

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

418sec/mjs#2 · Patch
cesanta/mjs release 1.26 · Release Notes
huntr.dev/bounties/1-other-mjs · Exploit

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