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CVE Record

CVE-2021-33438: An issue was discovered in mjs (mJS: Restricted JavaScript engine), ES6 (JavaScript version 6).

An issue was discovered in mjs (mJS: Restricted JavaScript engine), ES6 (JavaScript version 6). There is stack buffer overflow in json_parse_array() in mjs.c.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

CVE-2021-33438 is a reported stack buffer overflow in the mJS restricted JavaScript engine. The issue is in JSON array parsing. The public record does not name affected versions, a CVSS score, or a confirmed fix, so urgency depends on whether your software embeds mJS and processes untrusted input.

Executive priority

Set priority after confirming exposure. If mJS is not present, business urgency is low. If mJS is embedded in externally reachable systems, assign vulnerability-management follow-up because memory corruption in input parsing can affect availability and potentially security boundaries.

Technical view

The CVE describes a stack buffer overflow in json_parse_array() in mjs.c within mJS, a restricted JavaScript engine. The source bundle gives no CPEs, affected versions, CWE, CVSS vector, patch commit, or vendor remediation statement. Treat this as incomplete but relevant for products embedding mJS.

Likely exposure

Exposure is likely limited to applications, firmware, or services that embed Cesanta mJS or include mjs.c and process JSON arrays from untrusted or externally controlled input. The CVE source bundle does not identify specific affected products or versions.

Exploitation context

The CVE is not listed in KEV, and the provided sources do not state active exploitation in the wild. Public references include a GitHub issue and a gist, but the supplied evidence is insufficient to claim weaponized exploitation or broad scanning.

Researcher notes

The record is sparse: no CVSS, CWE, affected versions, CPEs, or fix are provided. Analysis should focus on confirming mJS embedding, input reachability, and upstream remediation status. Do not assume impact beyond the stated stack buffer overflow without additional vendor evidence.

Mitigation direction

  • Inventory software, firmware, and dependencies for embedded mJS or mjs.c usage.
  • Check Cesanta mJS guidance and issue history for a patched release or commit.
  • Contact downstream vendors if mJS is embedded in supplied products.
  • Restrict untrusted input reaching mJS JSON parsing where operationally feasible.
  • Monitor CVE and upstream references for remediation updates.

Validation and detection

  • Search code and SBOMs for Cesanta mJS, mjs.c, or mJS package references.
  • Confirm whether any exposed workflow parses user-controlled JSON with mJS.
  • Record exact embedded mJS version or commit where available.
  • Review upstream issue 158 and linked materials for vendor status.
  • Prioritize testing products that accept remote or unauthenticated input.
Prepared
Confidence
medium
Sources
4

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

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CVE-2021-33438 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
0Timeline events
0ADP providers
3Source links

CVSS and timeline data

No CVSS vectors or timeline events were available in the normalized CVE source material.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/an/an/aListed
Weakness

CWE details

No CWE listed

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.