LiveActive security incident?Get immediate response
CVE Record

CVE-2021-23436: Prototype Pollution

This affects the package immer before 9.0.6. A type confusion vulnerability can lead to a bypass of CVE-2020-28477 when the user-provided keys used in the path parameter are arrays. In particular, this bypass is possible because the condition (p === "__proto__" || p === "constructor") in applyPatches_ returns false if p is ['__proto__'] (or ['constructor']). The === operator (strict equality operator) returns false if the operands have different type.

MediumCVSS 5.6Not KEV-listedUpdated
Discuss exposureBack to CVEs
Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CVE-2021-23436 is a prototype pollution issue in Immer before 9.0.6. If an application lets untrusted users influence Immer patch paths, crafted array-shaped keys can bypass earlier protections and potentially affect confidentiality, integrity, and availability at low impact levels.

Executive priority

Treat as a moderate dependency risk. Prioritize applications that expose JSON or patch-like inputs to external users, then remediate remaining internal uses through normal dependency maintenance.

Technical view

Immer's applyPatches_ protection checked path elements with strict equality against "__proto__" and "constructor". Array path elements such as ["__proto__"] do not strictly equal those strings, creating a type confusion bypass of the earlier CVE-2020-28477 defense.

Likely exposure

Exposure is most likely in JavaScript applications or packaged dependencies using Immer before 9.0.6 and accepting user-controlled patch paths. Risk is lower where patches are internal-only or path data is strongly validated before reaching Immer.

Exploitation context

The source bundle does not show CISA KEV listing or active exploitation. CVSS indicates network reachability, no privileges, no user interaction, but high attack complexity and low confidentiality, integrity, and availability impact.

Researcher notes

Evidence supports a specific bypass in Immer's patch path filtering. The provided sources do not establish exploit-in-the-wild status. Validation should focus on reachability: whether attacker-controlled path arrays can reach Immer's patch application logic.

Mitigation direction

  • Upgrade Immer to 9.0.6 or later where present.
  • Check transitive dependencies and packaged WebJars copies for vulnerable Immer versions.
  • Reject untrusted patch paths containing prototype-related keys or unexpected array elements.
  • Review vendor advisories before relying on custom mitigations.
  • Regenerate lockfiles only through the normal dependency update process.

Validation and detection

  • Inspect SBOMs and lockfiles for Immer versions before 9.0.6.
  • Confirm deployed artifacts use the updated dependency version.
  • Identify APIs or routes accepting user-controlled patch/path data.
  • Verify validation rejects prototype-related path elements in all supported shapes.
  • Track the linked upstream commit and advisories in vulnerability records.
Prepared
Confidence
high
Sources
5

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-2021-23436 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
Medium
CVSS
5.6 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L/E:P/RL:O/RC:C

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.

1CVSS vectors
0Timeline events
0ADP providers
4Source links

CVSS vector scores

1 official score

We 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.

ScoreVersionSeverityVectorExploitImpactSource
5.6CVSS 3.1MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L/E:P/RL:O/RC:C2.23.4Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

5.6Medium
CVSS 3.1 vector shape for CVE-2021-23436Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L/E:P/RL:O/RC:C

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/aimmerunspecifiedListed
Weakness

CWE details

No CWE listed

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.