HOMEVULNERABILITIESCVE-2021-31875
CRITICAL

CVE-2021-31875

CWE-193Published: April 29, 2021· Updated: Jun 17, 2026

9.8
CVSS v3.1

Official 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."

NVD Source

Technical Analysis

CVE-2021-31875 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in complete confidentiality breach (data exposure), full integrity compromise (data manipulation), availability disruption (denial of service), with a CVSS base score of 9.8.

CVSS v3.1 Vector Breakdown

Exploitability
Attack VectorNetwork
Attack ComplexityLow
Privileges Req.None
User InteractionNone
ScopeUnchanged
Impact
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected Vendors & Products

cesanta1 product(s)
mongooseos mjs
Source: NVD CPE · 1 total CPE entries

Exploit & PoC Resources

NO KNOWN EXPLOITNo public exploit confirmed at this time
Exploit-DB
Offensive Security exploit database
GitHub PoC Search
Community PoC repositories
Rapid7 / Metasploit
Metasploit module search
PacketStorm
Security advisories & exploits
NVD Detail
Official NIST entry
MITRE CVE
CVE Program entry
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Official Patches & Advisories

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

All References (6)

→
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

Quick Facts

CVE IDCVE-2021-31875
CVSS Score9.8 / 10
SeverityCRITICAL
WeaknessCWE-193
CISA KEVNo
Affected1 vendor(s)
PublishedApr 29, 2021

Related CVEs (CWE-193)

CVE-2024-10442
10.0
CVE-2025-54349
10.0
CVE-2001-1496
9.8
CVE-2004-0005
9.8
CVE-2003-0356
9.8
CVE-2022-24988
9.8

Recommended Actions

  • →Apply vendor patches immediately
  • →Monitor CVE-2021-31875 in threat intel feeds
  • →Review IDS/IPS signatures for exploitation attempts
Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWATCH.COM. CVE data is provided under the NVD usage policy.
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