CVE-2026-55091Public exploitNetwork attack vector

Prototype pollution via inherited flat-record keys

Published Sep 14, 2026 · Updated Sep 14, 2026

Prototype pollution in flat-to-nested before 1.1.2 allows remote attackers to alter inherited object state through crafted records. FlatToNested.prototype.convert uses untrusted id and parent values as keys in plain temp and pendingChildOf objects, allowing proto to resolve to Object.prototype before initPush writes the configured children property. Reachability requires an application to pass attacker-influenced flat records to convert(); exploitation causes application-logic corruption or a service interrupt of unspecified form, while greater impact requires a downstream gadget.

CVSS severity7.5
High
EPSS probability0.36%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Prototype pollution in flat-to-nested before 1.1.2 allows remote attackers to alter inherited object state through crafted records. FlatToNested.prototype.convert uses untrusted id and parent values as keys in plain temp and pendingChildOf objects, allowing proto to resolve to Object.prototype before initPush writes the configured children property. Reachability requires an application to pass attacker-influenced flat records to convert(); exploitation causes application-logic corruption or a service interrupt of unspecified form, while greater impact requires a downstream gadget.

The record

CVE
CVE-2026-55091
Published
Sep 14, 2026
Updated
Sep 14, 2026
Vendor
joaonuno
Product
flat-to-nested
Classifications
CWE-915, CWE-1321
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 14, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 14, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 1.1.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

joaonuno · flat-to-nestedversion=< 1.1.2

Published CVSS scores

7.5GitHub Security AdvisoryCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-915Improperly Controlled Modification of Dynamically-Determined Object Attributes
CWE-1321Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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