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CVE Record

CVE-2021-33445: 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 NULL pointer dereference in mjs_string_char_code_at() 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-2021-33445 is a reported NULL pointer dereference in the mJS restricted JavaScript engine. The public record does not provide severity, CVSS, affected versions, or a named fix. Treat it mainly as a potential availability issue until upstream/vendor guidance clarifies impact.

Executive priority

Prioritize discovery over emergency response. Escalate if mJS is embedded in externally reachable services, devices, or automation paths processing untrusted scripts. Without affected-version and exploitation evidence, urgency is uncertain but should not be ignored.

Technical view

The issue is described in mjs_string_char_code_at() in mjs.c for mJS handling ES6 JavaScript. A NULL pointer dereference could crash a process using the engine if the vulnerable path is reachable. Version scope and remediation details are not provided in the supplied sources.

Likely exposure

Exposure is limited to systems that embed or vendor Cesanta mJS and allow JavaScript input to reach the affected string handling path. The CVE record lists no CPEs, products, or versions, so asset confirmation must be source-code or SBOM based.

Exploitation context

The source bundle includes public GitHub and gist references, but it does not show CISA KEV listing, active exploitation, or confirmed weaponized use. Public technical discussion exists; real-world risk depends on whether untrusted script input can reach mJS.

Researcher notes

The key evidence gap is scope: no affected versions, CPEs, CVSS, CWE, or remediation are present in the supplied CVE data. Analysis should focus on code reachability, provenance of vendored mJS copies, and upstream issue history rather than broad product assumptions.

Mitigation direction

  • Inventory applications, firmware, and dependencies for embedded Cesanta mJS or mjs.c.
  • Check the upstream GitHub issue and vendor guidance for fixed versions or recommended changes.
  • Restrict untrusted JavaScript input from reaching mJS until exposure is resolved.
  • If mJS is unnecessary in exposed paths, disable or isolate that functionality.
  • Track this CVE in vulnerability management despite missing CVSS data.

Validation and detection

  • Search SBOMs and source trees for cesanta/mjs, mjs.c, or mjs_string_char_code_at.
  • Confirm whether any discovered mJS copy matches the vulnerable code path.
  • Determine whether user-controlled JavaScript can execute through the embedded mJS engine.
  • Review upstream issue status for patches, commits, or maintainer guidance.
  • Add safe regression coverage for string charCodeAt handling if maintaining a fork.
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-2021-33445 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.