CVE-2025-15265Public exploitNetwork attack vector

Browser script execution via unescaped hydratable keys

Published Jan 15, 2026 · Updated Jan 15, 2026

Cross-site scripting in Svelte 5.46.0 through 5.46.3 allows remote attackers to execute JavaScript in users' browsers via crafted hydratable keys. Renderer.#hydratable_block in packages/svelte/src/internal/server/renderer.js serializes each key with JSON.stringify into an inline script, leaving less-than signs able to close the script element. Exploitation requires experimental.async, a hydratable key derived from untrusted input, and a user to load the server-rendered response; injected code then runs in that user's browser context.

CVSS severity5.3
Medium
EPSS probability0.35%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site scripting in Svelte 5.46.0 through 5.46.3 allows remote attackers to execute JavaScript in users' browsers via crafted hydratable keys. Renderer.#hydratable_block in packages/svelte/src/internal/server/renderer.js serializes each key with JSON.stringify into an inline script, leaving less-than signs able to close the script element. Exploitation requires experimental.async, a hydratable key derived from untrusted input, and a user to load the server-rendered response; injected code then runs in that user's browser context.

The record

CVE
CVE-2025-15265
Published
Jan 15, 2026
Updated
Jan 15, 2026
Vendor
Svelte
Product
Svelte
Classifications
CWE-79, CAPEC-63, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 15, 2026CVE publishedPublication date reported by the CVE source.
  2. Jan 15, 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=5.46.0 <5.46.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Svelte · Svelteversion=5.46.0 <5.46.3

Published CVSS scores

5.3Fluid AttacksCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA: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-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
CAPEC-63Cross-Site Scripting (XSS)
T1203Exploitation for Client Execution

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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