vulnerability / NVI-00018540 / Revision 1
Bleach: URI sanitization allows disallowed URI schemes with Unicode > U+00A0 in output
GitHub lists this reviewed advisory for bleach. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
bleach
source listed<= 6.3.0
### 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 = 'Click me' result1 = bleach.clean(payload1) print(f"(ZWSP): {repr(result1)}") ``` Output: ``` (ZWSP): 'Click me' ``` ### Pa
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. GitHub Advisory Database
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04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
05 / Provenance
Sources you can inspect
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- GHSA-8rfp-98v4-mmr6 ↗
GitHub Advisory Database · vendor advisory
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Public revision history
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- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.