CVE-2016-9909
Improper Neutralization of Input During Web Page Generation in html5lib
CVE-2016-9909 is a medium vulnerability (CVSS 6.1) in Html5lib, published January 3, 2017. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 2.16%, the 82nd percentile. Fixed in html5lib 0.999999999.
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.
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- Low
- Privileges needed
- None
- User interaction
- Required
What an attacker can affect
- Confidentiality
- Low
- Integrity
- Low
- Availability
- None
Exploit likelihood
What each source reports
NVD Score used
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.
- Record
CVE-2016-9909- CVSS 3.0
- 6.1 Medium
CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N - CVSS 2.0
- 4.3 Medium
AV:N/AC:M/Au:N/C:N/I:P/A:N - Weakness
- CWE-79
- Updated
- 2026-11-02
CVE List No score
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.
- Record
CVE-2016-9909- Updated
- 2026-11-02
EUVDEUVD-2017-0060 No score
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.
- Record
EUVD-2017-0060- Updated
- 2026-11-03
GitHub AdvisoriesGHSA-v9v9-xffq-rwr4
Improper Neutralization of Input During Web Page Generation in html5lib
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.
- Record
GHSA-v9v9-xffq-rwr4- CVSS 4.0
- 5.3 Medium
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N - CVSS 3.0
- 6.1 Medium
CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N - Weakness
- CWE-79
- Updated
- 2026-11-02
OSV
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.
- Record
CVE-2016-9909- CVSS 3.0
- 6.1 Medium
CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N - Updated
- 2026-11-02
OSVDEBIAN-CVE-2016-9909
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.
- Record
DEBIAN-CVE-2016-9909- CVSS 3.0
- 6.1 Medium
CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N - Updated
- 2026-11-02
Show 4 moreShow less
OSVGHSA-v9v9-xffq-rwr4
Improper Neutralization of Input During Web Page Generation in html5lib
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.
- Record
GHSA-v9v9-xffq-rwr4- CVSS 4.0
- 5.3 Medium
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N - CVSS 3.0
- 6.1 Medium
CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N - Weakness
- CWE-79
- Updated
- 2026-11-02
OSVUBUNTU-CVE-2016-9909
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.
- Record
UBUNTU-CVE-2016-9909- CVSS 3.0
- 6.1 Medium
CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N - Updated
- 2026-11-02
OSVMGASA-2017-0001 No score
Updated python-html5lib packages fix security vulnerability
Fixes a potential cross-site scripting vulnerablity: quote attributes that need escaping in legacy browsers. (CVE-2016-9909, CVE-2016-9910)
- Record
MGASA-2017-0001- Updated
- 2026-11-02
OSVPYSEC-2017-14 No score
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.
- Record
PYSEC-2017-14- Updated
- 2026-11-02
Affected products
Affected packages
| Package | Affected | Fixed |
|---|---|---|
html5libPyPI |
before 0.999999999 | 0.999999999 |
html5libDebian:12 |
before 0.999999999-1 | 0.999999999-1 |
html5libDebian:13 |
before 0.999999999-1 | 0.999999999-1 |
html5libDebian:14 |
before 0.999999999-1 | 0.999999999-1 |
html5libPyPI |
before 0.999999999, plus listed versions 0.100.110.11.10.20.9 Show 9 moreShow less0.900.950.990.9990.99990.999990.9999990.99999990.99999999 |
0.999999999 |
python-html5libMageia:5 |
before 1.0b3-7.1.mga5 | 1.0b3-7.1.mga5 |
html5libUbuntu:16.04:LTS |
All versions, plus listed versions 0.999-3build10.999-4 |
None known |
History
| When | Changed | Sources |
|---|---|---|
| 2026-11-03 | aliases | EUVD |
| 2026-11-02 | created | CVE List, GitHub Advisories, NVD, OSV |
References
github.com/html5lib/html5lib-python/issues/12
html5lib.readthedocs.io/en/latest/changes.html
openwall.com/lists/oss-security/2016/12/06/5
securityfocus.com/bid/95132
Show 12 moreShow less
nvd.nist.gov/vuln/detail/CVE-2016-9909
web.archive.org/web/20161229134056/http://www.securityfocus.com/bid/95132
security-tracker.debian.org/tracker/CVE-2016-9909
advisories.mageia.org/MGASA-2017-0001.html
bugs.mageia.org/show_bug.cgi?id=19912
ubuntu.com/security/CVE-2016-9909
sourceclear.com/registry/security/cross-site-scripting-xss-/python/sid-3068
cve.org/CVERecord?id=CVE-2016-9909