# GHSA-8rfp-98v4-mmr6: Bleach: URI sanitization allows disallowed URI schemes with Unicode > U+00A0 in output

> Bleach sanitizer fails to strip disallowed URI schemes containing Unicode characters, potentially allowing XSS if downstream systems normalize the output.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 16 Jun 2026

## What is GHSA-8rfp-98v4-mmr6?

GHSA-8rfp-98v4-mmr6 is a cross-site scripting vulnerability in bleach, published on 16 Jun 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

### Impact

A possible XSS bypass affects users calling `bleach.clean` with all of:

* `a` in the allowed tags
* `href` in allowed attributes

The `bleach.clean` sanitizer outputs URIs containing disallowed scheme patterns that it should be stripping. However, because the inserted Unicode characters make the scheme invalid per RFC 3986, modern browsers do not execute these as javascript: URIs. The practical security impact is limited to:

- Bleach's output contains URI values that violate the caller's protocol allowlist, breaking the sanitizer's contract.
- If a downstream system performs its own Unicode normalization on bleach's output (stripping invisible characters before rendering), the javascript: scheme could become valid. This is a non-standard processing chain but represents a theoretical secondary risk.

This is not a direct XSS vulnerability.

Python code example from reporter with Bleach v6.3.0 and Python 3.13:

```
import bleach
payload1 = '<a href="javascript\u200b:alert(document.cookie)">Click me</a>'
result1 = bleach.clean(payload1)
print(f"(ZWSP): {repr(result1)}")
```

Output:

```
(ZWSP): '<a href="javascript\u200b:alert(document.cookie)">Click me</a>'
```

### Patches

Users should upgrade to Bleach 6.4.0.

### Workarounds

Pre-process content removing non-ASCII characters from URI schemes before sanitizing with `bleach.clean`.

A strong[ Content-Security-Policy](https://developer.mozilla.org/en-US/docs/Web/HTTP/CSP) without unsafe-inline and unsafe-eval[ script-srcs](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy/script-src) will also help mitigate the risk.

### References

* https://bugzilla.mozilla.org/show_bug.cgi?id=2023812
* RFC 3986, Section 3.1 (URI Scheme syntax): scheme characters are restricted to ALPHA *( ALPHA / DIGIT / "+" / "-" / "." )

### Reported by 

Reported by codeant from CodeAnt AI.

## Which versions are affected by GHSA-8rfp-98v4-mmr6?

2 open source packages ship an affected version, including bleach.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `bleach` | PyPI | All versions | 6.4.0 |
| `bleach` | PyPI | All versions | 6.4.0 |

## How do I fix GHSA-8rfp-98v4-mmr6?

Upgrade bleach to 6.4.0 or later.

## Is GHSA-8rfp-98v4-mmr6 being exploited?

There is no known exploitation of GHSA-8rfp-98v4-mmr6 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for GHSA-8rfp-98v4-mmr6 and fix it if it is affected.

What it is: GHSA-8rfp-98v4-mmr6 is a cross-site scripting vulnerability in bleach, published on 16 Jun 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of GHSA-8rfp-98v4-mmr6 in the wild and no public exploit code.

Affected packages and fixed versions:
- bleach (PyPI): affected all versions; fixed in 6.4.0
- bleach (PyPI): affected all versions; fixed in 6.4.0

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/GHSA-8rfp-98v4-mmr6/ (Markdown: https://insights.sbomify.com/GHSA-8rfp-98v4-mmr6/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/GHSA-8rfp-98v4-mmr6

---
From sbomify Insights: https://insights.sbomify.com/GHSA-8rfp-98v4-mmr6/
Summaries are generated and may contain mistakes; the official description above is the record.