Is CVE-2016-9909 in the CISA KEV catalog?

No. CVE-2016-9909 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2016-9909?

CVE-2016-9909 has a CVSS v3 base score of 6.1 (MEDIUM).

What is the EPSS score for CVE-2016-9909?

CVE-2016-9909 has an EPSS score of 2.14% (80th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2016-9909?

Upgrade html5lib on debian 11 to 0.999999999-1 or later.

CVE & CISA-KEV Catalog

CVE-2016-9909

MEDIUMEPSS 80th pctl

6.1

CVSS v3

NVD

Description

The serializer in html5lib before 0.99999999 might allow remote attackers to conduct cross-site scripting (XSS) attacks by leveraging mishandling of the < (less than) character in attribute values.

CWE-79Cross-Site Scripting (XSS)

How to fix

Remediation Available

html5libDebian

Fixed in:0.999999999-1CVE-2016-9909

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionRequired

ScopeChanged

Impact

ConfidentialityLow

IntegrityLow

AvailabilityNone

CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Exploit Intelligence

2.14%probability of exploitation in 30 days

80thpercentile

Elevated risk: more likely to be exploited than 80% of all known CVEs.

References

Patch3

Vendor Advisory2

Third-Party Advisory1

securityfocus.com

Release Notes1

html5lib.readthedocs.io

Related Vulnerabilities

Other CWE-79 (Cross-Site Scripting (XSS)) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2020-11022	Medium	6.9	99%	-	Fix
CVE-2019-3929	Critical	9.8	99%	KEV	Fix
CVE-2020-9496	Medium	6.1	99%	-	-
CVE-2023-28341	Medium	6.1	99%	-	Fix
CVE-2018-12998	Medium	6.1	98%	-	-
CVE-2025-4123	High	7.6	98%	-	Fix

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-05-13.