# CVE-2026-31859: Craft has Reflective XSS via incomplete return URL sanitization

> Attackers can execute arbitrary JavaScript in victim browsers via unsanitized return URLs, potentially stealing cookies or session data.

- **Severity:** Medium 6.9 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 11 Mar 2026
- **Updated:** 12 Mar 2026
- **Also known as:** GHSA-fvwq-45qv-xvhv

## What is CVE-2026-31859?

CVE-2026-31859 is a medium-severity cross-site scripting vulnerability in Craftcms Craft Cms, published on 11 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Craft is a content management system (CMS). The fix for CVE-2025-35939 in craftcms/cms introduced a strip_tags() call in src/web/User.php to sanitize return URLs before they are stored in the session. However, strip_tags() only removes HTML tags (angle brackets) -- it does not inspect or filter URL schemes. Payloads like javascript:alert(document.cookie) contain no HTML tags and pass through strip_tags() completely unmodified, enabling reflected XSS when the return URL is rendered in an href attribute. This vulnerability is fixed in  5.9.7 and 4.17.3.

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation), CWE-116 (Improper Encoding or Escaping of Output)

## Which versions are affected by CVE-2026-31859?

4 open source packages ship an affected version, including craftcms/cms. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `craftcms/cms` | Packagist | From 4.15.3 | 4.17.3 |
| `craftcms/cms` | Packagist | From 4.15.3 | 4.17.3 |
| `craftcms/cms` | Packagist | From 5.7.5 | 5.9.7 |
| `craftcms/cms` | Packagist | From 5.7.5 | 5.9.7 |

Products: Craftcms Craft Cms.

## How do I fix CVE-2026-31859?

Upgrade craftcms/cms to a fixed version for your release line: 4.17.3 or 5.9.7.

## Is CVE-2026-31859 being exploited?

There is no known exploitation of CVE-2026-31859 in the wild and no public exploit code.

## Other vulnerabilities in Craftcms Craft Cms

- [CVE-2025-32432](https://insights.sbomify.com/CVE-2025-32432/): Craft CMS Code Injection (critical 10.0, exploited in the wild)
- [CVE-2024-56145](https://insights.sbomify.com/CVE-2024-56145/): Craft CMS Code Injection (critical 9.3, exploited in the wild)
- [CVE-2025-23209](https://insights.sbomify.com/CVE-2025-23209/): Craft CMS Code Injection (high 8.1, exploited in the wild)
- [CVE-2025-35939](https://insights.sbomify.com/CVE-2025-35939/): Craft CMS External Control of Assumed-Immutable Web Parameter (medium 6.9, exploited in the wild)
- [CVE-2023-41892](https://insights.sbomify.com/CVE-2023-41892/): Craft CMS Remote Code Execution vulnerability (critical 10.0)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-31859 and fix it if it is affected.

What it is: CVE-2026-31859 is a medium-severity cross-site scripting vulnerability in Craftcms Craft Cms, published on 11 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-31859 in the wild and no public exploit code.

Affected packages and fixed versions:
- craftcms/cms (Packagist): affected from 4.15.3; fixed in 4.17.3
- craftcms/cms (Packagist): affected from 4.15.3; fixed in 4.17.3
- craftcms/cms (Packagist): affected from 5.7.5; fixed in 5.9.7
- craftcms/cms (Packagist): affected from 5.7.5; fixed in 5.9.7

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-2026-31859/ (Markdown: https://insights.sbomify.com/CVE-2026-31859/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31859
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31859
- OSV: https://osv.dev/vulnerability/CVE-2026-31859

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31859/
Summaries are generated and may contain mistakes; the official description above is the record.