CVE-2026-27902

Svelte Vulnerable to XSS via HTML Comment Injection in SSR Error Boundary Hydration Markers

5.3 MediumFix available

Svelte performance oriented web framework. Prior to version 5.53.5, errors from transformError were not correctly escaped prior to being embedded in the HTML output, causing potential HTML injection and XSS if attacker-controlled content is returned from transformError. Version 5.53.5 fixes the issue.

Attack profile

How easy it is to exploit

Attack vector: Network
Complexity: High
Privileges needed: None
User interaction: Passive

What an attacker can affect

Confidentiality: Low
Integrity: None
Availability: None

Exploit likelihood

0.27%Up 0.2 points since Feb 26, 2026

What each source reports

CVE List Score used 5.3

Svelte Vulnerable to XSS via HTML Comment Injection in SSR Error Boundary Hydration Markers

Record: CVE-2026-27902
CVSS 4.0: 5.3 MediumCVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:P/VC:L/VI:N/VA:N/SC:H/SI:H/SA:N
Weakness: CWE-79
Updated: 2026-11-02

EUVDEUVD-2026-8800 5.3

Record: EUVD-2026-8800
CVSS 4.0: 5.3 MediumCVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:P/VC:L/VI:N/VA:N/SC:H/SI:H/SA:N
Updated: 2026-11-02

GitHub AdvisoriesGHSA-qgvg-pr8v-6rr3 5.3

Svelte: XSS via HTML Comment Injection in SSR Error Boundary Hydration Markers

Errors from transformError were not correctly escaped prior to being embedded in the HTML output, causing potential HTML injection and XSS if attacker-controlled content is returned from transformError.

Record: GHSA-qgvg-pr8v-6rr3
CVSS 4.0: 5.3 MediumCVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:P/VC:L/VI:N/VA:N/SC:H/SI:H/SA:N
Weakness: CWE-79
Updated: 2026-11-02

NVD 5.3

Record: CVE-2026-27902
CVSS 4.0: 5.3 MediumCVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:P/VC:L/VI:N/VA:N/SC:H/SI:H/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
CVSS 3.1: 5.4 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
Weakness: CWE-79
Updated: 2026-11-02

OSV 5.3

Svelte Vulnerable to XSS via HTML Comment Injection in SSR Error Boundary Hydration Markers

Record: CVE-2026-27902
CVSS 4.0: 5.3 MediumCVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:P/VC:L/VI:N/VA:N/SC:H/SI:H/SA:N
Weakness: CWE-79
Updated: 2026-11-02

OSVGHSA-qgvg-pr8v-6rr3 5.3

Svelte: XSS via HTML Comment Injection in SSR Error Boundary Hydration Markers

Record: GHSA-qgvg-pr8v-6rr3
CVSS 4.0: 5.3 MediumCVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:P/VC:L/VI:N/VA:N/SC:H/SI:H/SA:N
Weakness: CWE-79
Updated: 2026-11-02

Affected products

Affected packages

Affected packages
Package	Affected	Fixed
`svelte` npm	5.53.0 up to 5.53.5	5.53.5

History

History
Recorded	Changed	Sources
Nov 2, 2026	first indexed	CVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-27902 is a medium vulnerability (CVSS 5.3) in Svelte, published February 26, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.27%, the 19th percentile. Fixed in svelte 5.53.5.