Is This vulnerability exploited in the wild?

No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.

How severe is This vulnerability?

Low severity, with a CVSS score of 0, published 16 June 2026.

Is there a fix for This vulnerability?

A patch was published on 2026-06-05: Version 6.4.0 released Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is This vulnerability attacked?

It is attacked over the network, in a software library.

Check whether you run bleach (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Mozilla Bleach URI sanitization bypass via Unicode characters

Severity: low · CVSS 0 · Published 2026-06-16

Bleach is a Python library used to clean and sanitize HTML to prevent malicious code from running in web browsers. A flaw in its URI sanitization allows certain disallowed links (like those starting with 'javascript:') to pass through if they contain specific invisible Unicode characters. While most modern browsers will not execute these malformed links, they could become dangerous if another system processes the text further or if the browser's behavior changes, potentially leading to unauthorized script execution.

Technologies: bleach (PyPI). Vendors: PyPI.

Quick answers

Is This vulnerability exploited in the wild?: No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.
How severe is This vulnerability?: Low severity, with a CVSS score of 0, published 16 June 2026.
Which products and versions are affected?: bleach (PyPI) <= 6.3.0.
Is there a fix for This vulnerability?: A patch was published on 2026-06-05: Version 6.4.0 released Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is This vulnerability attacked?: It is attacked over the network, in a software library.
Am I affected?: Check whether you run bleach (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

A vulnerability in bleach.clean allows disallowed URI schemes (e.g., 'javascript:') to bypass the protocol allowlist if they contain Unicode characters above U+00A0, such as a Zero Width Space (U+200B). The root cause is an incomplete list of disallowed inputs (CWE-184) in the URI scheme validation logic, which fails to account for non-ASCII characters that break RFC 3986 compliance but may be normalized later. While modern browsers typically treat these as invalid URIs and do not execute them, a security risk exists if downstream systems perform Unicode normalization (stripping the invisible characters) before rendering the HTML. This could re-enable the 'javascript:' scheme and lead to Cross-Site Scripting (XSS). The issue is fixed in version 6.4.0.

Affected products

Mozilla bleach <= 6.3.0

Timeline

2026-06-05: advisory: Initial advisory published by maintainer
2026-06-16: disclosed: GitHub Advisory Database entry updated
2026-06-05: patched: Version 6.4.0 released

References

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