CVE-2025-57820Public exploitNetwork attack vector

Prototype pollution via unchecked deserialized object keys

Published Aug 26, 2025 · Updated Aug 27, 2025

Prototype pollution in Svelte devalue before 5.3.2 allows remote attackers to alter object behavior through crafted serialized input. The parse and unflatten hydration loop accepts proto keys and nonnumeric array indices, then assigns the resulting values to object properties. Exploitation requires a consuming application to pass attacker-controlled serialized data to these APIs; successful input can overwrite properties and bypass server-side validation.

CVSS severity7.9
High
EPSS probability0.37%
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 Svelte devalue before 5.3.2 allows remote attackers to alter object behavior through crafted serialized input. The parse and unflatten hydration loop accepts proto keys and nonnumeric array indices, then assigns the resulting values to object properties. Exploitation requires a consuming application to pass attacker-controlled serialized data to these APIs; successful input can overwrite properties and bypass server-side validation.

The record

CVE
CVE-2025-57820
Published
Aug 26, 2025
Updated
Aug 27, 2025
Vendor
Svelte
Product
devalue
Classifications
CWE-1321, CAPEC-180, CAPEC-77, CAPEC-1
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 26, 2025CVE publishedPublication date reported by the CVE source.
  2. Aug 27, 2025Record 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=< 5.3.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Svelte · devalueversion=< 5.3.2

Published CVSS scores

7.9GitHubCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:H

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-1321Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
CAPEC-180Exploiting Incorrectly Configured Access Control Security Levels
CAPEC-77Manipulating User-Controlled Variables
CAPEC-1Accessing Functionality Not Properly Constrained by ACLs

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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