CVE-2018-19787 — An issue was discovered in lxml before 4

An issue was discovered in lxml before 4.2.5. lxml/html/clean.py in the lxml.html.clean module does not remove javascript: URLs that use escaping, allowing a remote attacker to conduct XSS attacks, as demonstrated by "j a v a s c r i p t:" in Internet Explorer. This is

01What is this vulnerability?

An issue was discovered in lxml before 4.2.5. lxml/html/clean.py in the lxml.html.clean module does not remove javascript: URLs that use escaping, allowing a remote attacker to conduct XSS attacks, as demonstrated by "j a v a s c r i p t:" in Internet Explorer. This is a similar issue to CVE-2014-3146.

02Affected products

Vendor	Product	Versions
n	a / n/a	n/a

03Active exploitation status

Not currently listed on the CISA Known Exploited Vulnerabilities (KEV) catalog. EPSS is the best forward-looking signal — see the EPSS row above.

04Recommended remediation

• Patch to a fixed version listed in the vendor advisory (see references below).
• Mitigate with WAF rules, network egress filters, or feature flags where the patch is not yet available.
• Hunt historical logs for exploitation indicators — see Detection signatures below.

05Technical details

For the full vendor write-up, exploit chains, and reference implementations, see the references list in section 09.

06Detection signatures

Ask SARA in chat to draft a starting detection for this CVE in your stack of choice.

07Related CVEs

08Timeline

• Published: 2018-12-02T10:00:00.000Z
• Last modified: 2025-12-18T15:15:39.190Z

09References

• usn.ubuntu.com — https://usn.ubuntu.com/3841-1/
• lists.debian.org — https://lists.debian.org/debian-lts-announce/2018/12/msg00001.html
• usn.ubuntu.com — https://usn.ubuntu.com/3841-2/
• github.com — https://github.com/lxml/lxml/commit/6be1d081b49c97cfd7b3fbd934a193b668629109
• lists.debian.org — https://lists.debian.org/debian-lts-announce/2020/11/msg00044.html