LiveActive security incident?Get immediate response
CVE Record

CVE-2021-26707: The merge-deep library before 3.0.3 for Node.js can be tricked into overwriting properties of Object.protot...

The merge-deep library before 3.0.3 for Node.js can be tricked into overwriting properties of Object.prototype or adding new properties to it. These properties are then inherited by every object in the program, thus facilitating prototype-pollution attacks against applications using this library.

UnknownCVSS not scoredNot KEV-listedUpdated
Discuss exposureBack to CVEs
Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

Applications using older merge-deep may let attacker-controlled data change shared object defaults inside a Node.js process. That can create unpredictable behavior beyond one request or object. The bundle does not provide CVSS or confirmed exploit activity, so urgency depends on whether untrusted input reaches this library.

Executive priority

Treat this as a dependency hygiene and application exposure issue. Prioritize internet-facing or customer-data-handling Node.js services first, especially where untrusted input is merged into application objects. No active exploitation is cited in the provided sources.

Technical view

merge-deep before 3.0.3 can be tricked into overwriting or adding properties on Object.prototype during deep merge operations. Those inherited properties can affect every object in the program, enabling prototype-pollution attacks against applications using this library.

Likely exposure

Exposure is most likely in Node.js applications or packages that depend on merge-deep below 3.0.3 and merge attacker-controlled objects. The CVE record's affected product metadata is incomplete, so dependency inventory is required.

Exploitation context

Sources describe a prototype-pollution condition, but the bundle does not cite CISA KEV listing or active exploitation. Practical impact depends on application-specific data flow and whether polluted inherited properties influence authorization, configuration, rendering, or other sensitive logic.

Researcher notes

The source bundle gives the core flaw and fixed threshold but lacks CVSS, CWE, and precise affected CPE data. Validate exposure through dependency trees and code paths, not product metadata alone. Do not assume exploitability without an untrusted merge path.

Mitigation direction

  • Upgrade merge-deep to 3.0.3 or later where dependency constraints allow.
  • Review transitive dependencies for older merge-deep versions.
  • Check package and vendor advisories before applying production changes.
  • Reduce or block untrusted object merging in affected application paths.
  • Add regression coverage around unsafe prototype keys in merge inputs.

Validation and detection

  • Inventory direct and transitive merge-deep versions in Node.js projects.
  • Identify routes or jobs that pass user-controlled objects into deep merge logic.
  • Confirm upgraded builds no longer include merge-deep before 3.0.3.
  • Review tests for prototype-pollution regression scenarios.
  • Check vendor advisories for affected downstream products.
Prepared
Confidence
high
Sources
6

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

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cve · low confidence lookup

CVE-2021-26707 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

Open ATT&CK lookup
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
5Source 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.