Security readout for executives and security teams
Plain-English summary
MuJS before 1.1.2 has a memory safety bug tied to reading a regular expression's source property. The source bundle says this may cause denial of service. The CVSS score is critical, but the provided evidence does not confirm active exploitation or broader impact beyond the listed description.
Executive priority
Treat as high-priority for systems that expose MuJS to untrusted input. The critical CVSS warrants prompt inventory and remediation, but business urgency depends on whether MuJS is actually deployed and reachable.
Technical view
CVE-2021-33796 is a CWE-416 use-after-free in MuJS regexp source property access. The affected product is MuJS, with version 1.1.1 listed and the title indicating versions before 1.1.2. The only fix evidence provided is the upstream GitHub commit reference.
Likely exposure
Exposure is most likely where MuJS is embedded in applications, appliances, scripts, or services that evaluate or parse untrusted JavaScript. The bundle does not identify downstream products using vulnerable MuJS.
Exploitation context
The source bundle marks CISA KEV as false and provides no cited evidence of active exploitation. It describes denial of service as the known impact. Do not assume exploitation in the wild without additional vendor or threat intelligence confirmation.
Researcher notes
The evidence is sparse: it identifies a use-after-free, affected MuJS version range, CVSS 10, and an upstream commit. The public bundle does not provide exploit details, downstream affected products, or confirmed in-the-wild exploitation.
Mitigation direction
- Inventory applications and appliances that embed MuJS.
- Upgrade MuJS to version 1.1.2 or later where applicable.
- Check vendor advisories for downstream products bundling MuJS.
- Prioritize systems processing untrusted JavaScript or regular expressions.
- Restrict untrusted JavaScript processing until vendor guidance is confirmed.
Validation and detection
- Confirm whether MuJS is present in source, packages, firmware, or SBOMs.
- Verify deployed MuJS versions are not before 1.1.2.
- Check whether the referenced upstream fix is included in vendored code.
- Review services that expose MuJS processing to untrusted input.
- Record compensating controls if immediate upgrade is not possible.
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-416: 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-2021-33796 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
- Critical
- CVSS
- 10 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/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:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H3.96Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
10CriticalVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/ccxvii/mujs/commit/7ef066a3bb95bf83e7c5be50d859e62e58fe8515CVE 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.
Use After Free
Use After Free represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.