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CVE Record

CVE-2021-33449: 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_bcode_part_get_by_offset() 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-2021-33449 is a crash-class flaw in mJS, a restricted JavaScript engine. The public record describes a null pointer dereference, but does not provide severity scoring, affected versions, or a named fix. Business urgency depends on whether mJS is embedded in products that process attacker-controlled JavaScript.

Executive priority

Prioritize discovery over emergency response. There is no supplied evidence of active exploitation or a known severity score, but embedded JavaScript engines can sit inside products unnoticed. Confirm whether mJS exists in the environment, then follow vendor guidance if exposure is found.

Technical view

The CVE describes a NULL pointer dereference in mjs_bcode_part_get_by_offset() in mjs.c. The supplied sources identify mJS and ES6 context, but provide no CVSS, CWE, affected version range, or patch reference. Treat this as incomplete public evidence requiring product-specific validation.

Likely exposure

Exposure is likely limited to software, firmware, or services embedding cesanta/mjs and allowing JavaScript input to reach the vulnerable bytecode lookup path. The CVE record lists affected vendor/product/version as n/a, so exposure cannot be confirmed from the supplied sources alone.

Exploitation context

The supplied sources do not show CISA KEV listing or active exploitation evidence. The GitHub issue and gist appear to document the crash condition, but the source bundle does not establish real-world exploitation, remote reachability, authentication requirements, or affected release boundaries.

Researcher notes

The public metadata is sparse: no CVSS, no CWE, no affected version range, and no named patch in the supplied CVE data. Analysis should focus on reachability, embedded use, and whether the referenced crash applies to the organization’s specific mJS version or fork.

Mitigation direction

  • Inventory products, firmware, and services that embed cesanta/mjs.
  • Check mJS project and vendor guidance for fixed releases or workarounds.
  • Upgrade or patch only according to confirmed vendor or project guidance.
  • Avoid exposing mJS JavaScript processing to untrusted input where feasible.
  • Monitor the CVE record and referenced issue for updated affected-version details.

Validation and detection

  • Confirm whether any deployed component includes cesanta/mjs.
  • Identify the exact mJS version, fork, or vendored commit in each component.
  • Review crash telemetry for mjs_bcode_part_get_by_offset() null dereferences.
  • Check whether JavaScript input can be supplied by unauthenticated or low-trust users.
  • Document unknowns where affected versions or fixes cannot be confirmed.
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-2021-33449 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.