# CVE-2026-27122: Svelte SSR does not validate dynamic element tag names in `<svelte:element>`

> An attacker can inject malicious HTML into server-side rendered output via unsanitized dynamic element tags in Svelte, potentially leading to XSS.

- **Severity:** Medium 5.1 (`CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:L/VI:N/VA:N/SC:H/SI:H/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 20 Feb 2026
- **Updated:** 23 Feb 2026
- **Also known as:** GHSA-m56q-vw4c-c2cp

## What is CVE-2026-27122?

CVE-2026-27122 is a medium-severity cross-site scripting vulnerability in sveltejs svelte, published on 20 Feb 2026. An attacker needs administrator access to exploit it, with no action from the victim.

### Official description

svelte performance oriented web framework. Prior to 5.51.5, when using <svelte:element this={tag}> in server-side rendering, the provided tag name is not validated or sanitized before being emitted into the HTML output. If the tag string contains unexpected characters, it can result in HTML injection in the SSR output. Client-side rendering is not affected. This vulnerability is fixed in 5.51.5.

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation)

## Which versions are affected by CVE-2026-27122?

2 open source packages ship an affected version, including svelte. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `svelte` | npm | All versions | 5.51.5 |
| `svelte` | npm | All versions | 5.51.5 |

Products: Svelte Svelte.

## How do I fix CVE-2026-27122?

Upgrade svelte to 5.51.5 or later.

## Is CVE-2026-27122 being exploited?

There is no known exploitation of CVE-2026-27122 in the wild and no public exploit code.

## Other vulnerabilities in sveltejs svelte

- [CVE-2021-29261](https://insights.sbomify.com/CVE-2021-29261/): Code injection in n/a (high 7.8)
- [CVE-2026-42567](https://insights.sbomify.com/CVE-2026-42567/): Svelte: ReDoS in `<svelte:element>` Tag Validation (medium 5.9)
- [CVE-2024-45047](https://insights.sbomify.com/CVE-2024-45047/): Potential mXSS vulnerability due to improper HTML escaping in svelte (medium 5.4)
- [CVE-2022-25875](https://insights.sbomify.com/CVE-2022-25875/): Cross-site Scripting (XSS) (medium 5.4)
- [CVE-2026-42573](https://insights.sbomify.com/CVE-2026-42573/): Svelte: XSS via DOM Clobbering of Internal Framework State (medium 5.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-27122 and fix it if it is affected.

What it is: CVE-2026-27122 is a medium-severity cross-site scripting vulnerability in sveltejs svelte, published on 20 Feb 2026. An attacker needs administrator access to exploit it, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-27122 in the wild and no public exploit code.

Affected packages and fixed versions:
- svelte (npm): affected all versions; fixed in 5.51.5
- svelte (npm): affected all versions; fixed in 5.51.5

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-27122/ (Markdown: https://insights.sbomify.com/CVE-2026-27122/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-27122
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-27122
- OSV: https://osv.dev/vulnerability/CVE-2026-27122

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-27122/
Summaries are generated and may contain mistakes; the official description above is the record.