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CVE Record

CVE-2021-39138: New anonymous user session acts as if it's created with password

Parse Server is an open source backend that can be deployed to any infrastructure that can run Node.js. Developers can use the REST API to signup users and also allow users to login anonymously. Prior to version 4.5.1, when an anonymous user is first signed up using REST, the server creates session incorrectly. Particularly, the `authProvider` field in `_Session` class under `createdWith` shows the user logged in creating a password. If a developer later depends on the `createdWith` field to provide a different level of access between a password user and anonymous user, the server incorrectly classified the session type as being created with a `password`. The server does not currently use `createdWith` to make decisions about internal functions, so if a developer is not using `createdWith` directly, they are not affected. The vulnerability only affects users who depend on `createdWith` by using it directly. The issue is patched in Parse Server version 4.5.1. As a workaround, do not use the `createdWith` Session field to make decisions if one allows anonymous login.

MediumCVSS 4.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

Parse Server could label a new anonymous REST session as created with a password. If an application trusted that label to grant stronger access, anonymous users could be treated like password users. Parse Server itself does not use the label internally, so risk is limited to custom application logic.

Executive priority

Prioritize remediation where anonymous login is enabled and custom authorization depends on session metadata. Otherwise, treat as a contained medium-risk library update.

Technical view

Before 4.5.1, REST anonymous signup populated _Session.createdWith.authProvider as password. The issue is CWE-287 with CVSS 4.8. Affected software is parse-server below 4.5.1. Impact depends on developers directly using createdWith for authorization or trust decisions.

Likely exposure

Exposure is likely in Parse Server deployments below 4.5.1 that allow anonymous login and directly use _Session.createdWith to distinguish anonymous and password sessions.

Exploitation context

The bundle provides no KEV listing or active exploitation evidence. The advisory says Parse Server internal functions do not rely on createdWith, so exploitation requires application-specific logic that trusts this session field.

Researcher notes

The core defect is incorrect session metadata, not a documented server-side authorization bypass. Validate exposure by tracing application use of createdWith. Do not assume impact without proving business logic trusts that field.

Mitigation direction

  • Upgrade Parse Server to version 4.5.1 or later.
  • Stop using _Session.createdWith for access decisions.
  • Review vendor advisory and 4.5.1 release notes.
  • Audit custom authorization logic around anonymous users.
  • Add tests for anonymous versus password-user access boundaries.

Validation and detection

  • Inventory deployed parse-server versions and confirm 4.5.1 or later.
  • Confirm whether anonymous login is enabled.
  • Search application code for _Session.createdWith or authProvider checks.
  • Review access-control tests covering anonymous sessions.
  • Verify production deployments use the patched package version.
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.

cwe · medium confidence lookup

CWE-287: Credential and account abuse lookup

Authentication and credential weaknesses can make valid-account abuse and credential telemetry useful review starting points. 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 lookup
description · low confidence lookup

Credential and access behavior lookup

The CVE wording references authentication or credential exposure, so valid-account and credential-access review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.

Open ATT&CK lookup
cve · low confidence lookup

CVE-2021-39138 mapping review

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Vulnerability profileCVE Program record
Severity
Medium
CVSS
4.8 (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:N

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
4.8CVSS 3.1MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N2.22.5Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

4.8Medium
CVSS 3.1 vector shape for CVE-2021-39138Attack 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:N

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
parse-communityparse-server< 4.5.1Listed
Weakness

CWE details

CWE-287

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

CWE-287 · source CWE mapping

Improper Authentication

Improper Authentication represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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