Security readout for executives and security teams
Plain-English summary
CVE-2021-36535 is a buffer overflow in Cesanta mJS 1.26 that can crash affected software when it processes a crafted JavaScript file. The documented impact is denial of service, not data theft or code execution. Exposure depends on whether mJS 1.26 is embedded in your products or services.
Executive priority
Treat this as a moderate availability risk. Prioritize systems where JavaScript input can affect customer-facing services, embedded devices, or operational technology. The main business concern is service disruption, with urgency driven by confirmed use of mJS 1.26 and input exposure.
Technical view
The CVE describes a CWE-787 out-of-bounds write in mJS 1.26 involving mjs_set_errorf. The CVSS 3.1 score is 5.5 with availability impact only. The record lacks CPEs and the affected metadata is incomplete, so product exposure must be confirmed by dependency and embedded-component review.
Likely exposure
Most likely exposure is software, firmware, or internal tooling that embeds Cesanta mJS 1.26 and processes JavaScript files from users, tenants, integrations, or update channels. The source bundle does not identify packaged downstream products.
Exploitation context
The source bundle supports denial of service via a crafted .js file. It does not show CISA KEV listing, confirmed active exploitation, exploit maturity, or a vendor-named patch. The description says remote attackers, while CVSS marks local attack vector, so practical reachability is unclear.
Researcher notes
Key uncertainties are downstream affected products, fixed version, and attack vector. The CVSS vector is AV:L/PR:L/UI:N with availability-only impact, but the description references remote attackers. Avoid assuming remote exploitability unless your deployment exposes mJS processing to attacker-controlled files.
Mitigation direction
- Inventory applications, firmware, and vendors for embedded Cesanta mJS 1.26 usage.
- Check Cesanta mJS issue 175 and vendor guidance for fixed versions or recommended handling.
- Avoid processing untrusted JavaScript through affected mJS deployments where feasible.
- Reduce service impact with isolation, watchdog restarts, and availability monitoring.
- Ask downstream suppliers whether their products include vulnerable mJS code.
Validation and detection
- Review SBOMs, lockfiles, vendored source, and firmware manifests for mJS 1.26.
- Confirm whether exposed workflows accept or generate JavaScript files processed by mJS.
- Compare findings against the CVE record and GitHub issue details.
- Validate any remediation in a non-production environment using vendor-approved tests.
- Document systems where version or reachability cannot be confirmed.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
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
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-787: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2021-36535 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Medium
- CVSS
- 5.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
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.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H1.83.6Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
5.5MediumVector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/cesanta/mjs/issues/175CVE reference
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Out-of-bounds Write
Out-of-bounds Write represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.