CVE-2020-7637Public exploitNetwork attack vector

Prototype pollution via unsafe transformation keys

Published Apr 6, 2020 · Updated Aug 4, 2024

Prototype pollution in TypeStack class-transformer before 0.3.1 allows attackers to modify Object.prototype through crafted input. The classToPlainFromExist transformation loop copies untrusted keys without rejecting proto or constructor, allowing inherited properties to be created or changed. Exploitation requires a consuming application to pass attacker-controlled object keys into this path, after which inherited properties can alter application logic.

CVSS severity5.3
Medium
EPSS probability1.19%
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 TypeStack class-transformer before 0.3.1 allows attackers to modify Object.prototype through crafted input. The classToPlainFromExist transformation loop copies untrusted keys without rejecting proto or constructor, allowing inherited properties to be created or changed. Exploitation requires a consuming application to pass attacker-controlled object keys into this path, after which inherited properties can alter application logic.

The record

CVE
CVE-2020-7637
Published
Apr 6, 2020
Updated
Aug 4, 2024
Vendor
TypeStack
Product
class-transformer
Classifications
CWE-915, CWE-1321
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 6, 2020CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record 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=All versions prior to version 0.3.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

TypeStack · class-transformerversion=All versions prior to version 0.3.1

Published CVSS scores

5.0National Vulnerability DatabaseAV:N/AC:L/Au:N/C:N/I:P/A:N
5.3National Vulnerability DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 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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