What is the CVSS score of CVE-2026-27121?

CVE-2026-27121 has a CVSS 3.1 base score of 5.4 (Medium). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N. EPSS exploitation probability: 0.0%.

Which versions of Svelte are affected by CVE-2026-27121?

CVE-2026-27121 presents moderate security risk, a cross-site scripting vulnerability rated CVSS 5.4. Attackers could inject scripts to steal sessions or perform actions as authenticated users.. A patch is available.

How to fix or mitigate CVE-2026-27121?

Within 30 days: Identify affected systems and apply vendor patches as part of regular patch cycle. Verify Content-Security-Policy and output encoding.

Svelte CVE-2026-27121

MEDIUM

Cross-site Scripting (XSS) (CWE-79)

2026-02-20 security-advisories@github.com

GHSA-f7gr-6p89-r883

XSS Svelte Red Hat

5.4

CVSS 3.1 · GitHub Advisory

Severity by source

GitHub Advisory PRIMARY

5.4 MEDIUM

AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

Red Hat

5.6 MEDIUM

qualitative

Primary rating from GitHub Advisory.

CVSS VectorGitHub Advisory

CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

Attack Vector

Network

Attack Complexity

Low

Privileges Required

Low

User Interaction

Required

Scope

Changed

Confidentiality

Low

Integrity

Low

Availability

None

Lifecycle Timeline

Patch released

Mar 31, 2026 - 21:13 nvd

Patch available

Analysis Generated

Mar 12, 2026 - 22:04 vuln.today

CVE Published

Feb 20, 2026 - 23:16 nvd

MEDIUM 5.4

Blast Radius

ecosystem impact

† from your stack dependencies † transitive graph · vuln.today resolves 4-path depth

1 npm packages depend on svelte (1 direct, 0 indirect)

Ecosystem-wide dependent count for version 5.51.5.

DescriptionGitHub Advisory

svelte performance oriented web framework. Versions of svelte prior to 5.51.5 are vulnerable to cross-site scripting (XSS) during server-side rendering. 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. This vulnerability is fixed in 5.51.5.

AnalysisAI

Server-side rendering in Svelte versions before 5.51.5 fails to sanitize event handler properties when spreading untrusted data as HTML attributes, enabling stored or reflected XSS attacks. An attacker can inject malicious event handlers into rendered pages if an application spreads user-controlled or external data as element attributes, causing arbitrary JavaScript execution in victim browsers. …

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Vulnerability AssessmentAI

Risk Assessment	CVSS 5.4 (MEDIUM). … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario	An attacker could exploit this vulnerability to compromise the affected system.
Remediation	Fixed in version 5.51.5.. … Detailed patch versions, workarounds, and compensating controls in full report.

Recommended ActionAI

Within 30 days: Identify affected systems and apply vendor patches as part of regular patch cycle. …

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Vendor StatusVendor

CVE-2026-27121 vulnerability details – vuln.today

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