CVE-2021-31875

Exp

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."

Published: 2021-04-28 Last update: 2026-06-16 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-31875 is rated High Exploit Risk (83.7/100): CVSS Critical severity, with medium exploitation likelihood (EPSS 2.17%). 1 public exploit reference(s) are indexed (Exploit-DB). EPSS rose +1.56% over the last day, indicating growing attacker interest. Public exploits are available—assess exposure, apply mitigations, and prioritize patching.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Public exploit references (Exploit-DB) for CVE-2021-31875

EDB-ID Source Kind Published Link
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2021-31875

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.61% 2.17% +1.56%
2 2026-06-01 0.55% 0.61% +0.06%
3 2025-11-21 — 0.55% —

Full EPSS history (18 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-31875

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
9.8 3.1 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 5.9 [email protected]
7.5 2.0 HIGH
AV:N/AC:L/Au:N/C:P/I:P/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:P)
Partial availability impact.
 10.0 6.4 [email protected]

Weakness enumeration for CVE-2021-31875

Affected software / configurations for CVE-2021-31875

Vendor Product Version Raw CPE
cesanta mongooseos_mjs 1.26 cpe:2.3:a:cesanta:mongooseos_mjs:1.26:*:*:*:*:*:*:*

References for CVE-2021-31875

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