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CVE-2026-42599· NVD / CVE Program· CNA GitHub_M

Cross-site scripting via spread attributes in Svelte SSR

Svelte is a performance oriented web framework. Prior to version 5.55.7, when using spread syntax to render attributes from untrusted data, event handler properties are included in the rendered HTML output. If an application spreads user-controlled or external data as element attributes, an attacker can inject malicious event handlers that execute in victims' browsers. Note that this vulnerability only triggers if the user's browser has JavaScript enabled but Svelte's hydration mechanism does not reach the vulnerable element before the event fires. This issue has been patched in version 5.55.7.

MediumCVSS 5.1 · v4.0—No exploit Fix available

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Published
Jun 9, 2026
Updated
Jul 23, 2026
EPSS
0.2% · 13th percentile
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Report tools

JSON

Action score

20

Monitor

Low priority for now.

CVSS
20 / 40 · 5.1 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.2%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · GitHub_M
5.1
NVD has not scored this yet; the score shown is the CNA’s.

CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Affected systems

VendorProduct
sveltesvelte

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • svelte sveltebefore 5.55.7

Versions reported by the vendor

Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.

  • sveltejs svelte

    • < 5.55.7affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
npmsveltebefore 5.55.75.55.7

Same product

svelte: all records

Other highest-scoring records for the same primary product.

  • CVE-2021-29261The unofficial Svelte extension before 104.8.0 for Visual Studio Code allows attackers to execute arbitrary code via a crafted workspace con
    31Monitor
  • CVE-2024-45047Potential mXSS vulnerability due to improper HTML escaping in svelte
    24Monitor
  • CVE-2022-25875Cross-site Scripting (XSS)
    24Monitor
  • CVE-2026-42567Svelte: ReDoS in `<svelte:element>` Tag Validation
    23Monitor
  • CVE-2026-42573Svelte: XSS via DOM Clobbering of Internal Framework State
    21Monitor
  • CVE-2026-27902Svelte Vulnerable to XSS via HTML Comment Injection in SSR Error Boundary Hydration Markers
    21Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
sveltejs svelte5.55.7 · descriptionVendor (CNA)
npm:svelte5.55.7Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

  • CVE-2026-425730 days apartSvelte: XSS via DOM Clobbering of Internal Framework State
    21Monitor
  • CVE-2026-27901104 days apartSvelte vulnerable to XSS during SSR with contenteditable `bind:innerText` and `bind:textContent`
    21Monitor
  • CVE-2026-27902104 days apartSvelte Vulnerable to XSS via HTML Comment Injection in SSR Error Boundary Hydration Markers
    21Monitor
  • CVE-2025-15265145 days apartSvelte 5.46.0 - Hydratable Key Script-Breakout XSS (SSR)
    21Monitor
  • CVE-2026-27119109 days apartSvelte affected by XSS in SSR `<option>` element
    20Monitor
  • CVE-2026-27121109 days apartSvelte affected by cross-site scripting via spread attributes in Svelte SSR
    20Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

The product’s vendor appears in a public program. Matched by name; verify the scope text in the program.

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • Administrator privileges are required.
  • No user action is required.
  • Special conditions such as timing or configuration are required.

If successful

Confidentiality
Integrity
Availability
Attack vector
Network
Attack complexity
High
Privileges required
High
User interaction
None
Scope
X

Weakness class (CWE)

CWE-79 · Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

CVSS vector

CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:N/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

nvd-secondary

Root cause

User content is inserted into the page as HTML. The browser interprets the content as code rather than data.

The bug in code

The whole CWE-79 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

ts
commentEl.innerHTML = comment.body;

Fixed

ts
commentEl.textContent = comment.body;

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records