Security readout for executives and security teams
Plain-English summary
CVE-2021-23663 is a medium-severity prototype pollution issue in the npm package sey. The risk matters when an application uses sey to merge attacker-controlled structured data. Successful abuse could alter application object behavior, causing limited integrity changes or availability impact.
Executive priority
Treat this as a targeted dependency hygiene issue, not an emergency unless sey is used on exposed input-processing paths. Prioritize affected internet-facing services and software supply-chain cleanup.
Technical view
The reported flaw affects all versions of sey through its deepmerge() function. The CVSS 3.1 vector is 6.5, network-exploitable, low complexity, no privileges or user interaction, with low integrity and availability impact and no confidentiality impact.
Likely exposure
Exposure is most likely in Node.js applications that include sey directly or through dependency chains and process untrusted nested objects with deepmerge(). The source bundle does not identify specific platforms, applications, or deployed services beyond the package itself.
Exploitation context
The CVSS vector marks exploit maturity as proof-of-concept. The bundle does not show CISA KEV listing or cited evidence of active exploitation in the wild, so active exploitation should not be assumed.
Researcher notes
Evidence is limited to public advisory data in the bundle. The advisory identifies sey deepmerge() and prototype pollution but does not provide patch details, affected downstream products, or active exploitation evidence.
Mitigation direction
- Inventory direct and transitive sey dependencies in affected applications.
- Check Snyk or vendor guidance for fixed-version or replacement advice.
- Avoid passing untrusted structured data into sey deepmerge().
- Add input validation for object keys before merge operations.
- Prioritize remediation where internet-facing APIs process JSON or form data.
Validation and detection
- Confirm whether sey appears in dependency manifests or lockfiles.
- Trace application code paths that call deepmerge() with user-controlled data.
- Review dependency scanner results for SNYK-JS-SEY-1727592 or CVE-2021-23663.
- Test that merge paths reject unsafe object keys without causing regressions.
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
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CVE-2021-23663 mapping review
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Open ATT&CK lookup- Severity
- Medium
- CVSS
- 6.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L/E:P
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:U/C:N/I:L/A:L/E:P3.92.5Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
6.5MediumVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L/E:P
Source materials
- CVE List V5 sourceCVE List V5
- https://snyk.io/vuln/SNYK-JS-SEY-1727592CVE reference · x_refsource_MISC
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.