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No exploitation reportedFix available

CVE-2020-27783

No exploitation reported by the sources we read.

  • Published2020-12-03
  • WeaknessCWE-79

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

A XSS vulnerability was discovered in python-lxml's clean module. The module's parser didn't properly imitate browsers, which caused different behaviors between the sanitizer and the user's page. A remote attacker could exploit this flaw to run arbitrary HTML/JS code.

Timeline

dates in UTC
  1. 2020-12-0317:15CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 21:37 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2020-27783?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2020-27783?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD · OSV
Debian debian linux
BranchAffectedFixed in
9.0= 9.0no fix published
10.0= 10.0no fix published
Fedoraproject fedora
BranchAffectedFixed in
32.x= 32no fix published
33.x= 33no fix published
Lxml
BranchAffectedFixed in
4.6≥ 1.2, < 4.6.24.6.2
4.6< 4.6.24.6.2

5 more products in the sources.

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • python-sqlalchemy-docAlmaLinux:8all versions · fixed in 1.3.2-2.module_el8.5.0+2569+5c5719bc
  • python2-attrsAlmaLinux:8all versions · fixed in 17.4.0-10.module_el8.6.0+2781+fed64c13
  • python2-backportsAlmaLinux:8all versions · fixed in 1.0-16.module_el8.6.0+2781+fed64c13
  • python2-backports-ssl_match_hostnameAlmaLinux:8all versions · fixed in 3.5.0.1-12.module_el8.6.0+2781+fed64c13
  • python2-chardetAlmaLinux:8all versions · fixed in 3.0.4-10.module_el8.6.0+2781+fed64c13
  • python2-coverageAlmaLinux:8all versions · fixed in 4.5.1-4.module_el8.6.0+2781+fed64c13
  • python2-CythonAlmaLinux:8all versions · fixed in 0.28.1-7.module_el8.6.0+2781+fed64c13
  • python2-dnsAlmaLinux:8all versions · fixed in 1.15.0-10.module_el8.6.0+2781+fed64c13

41 more package ranges on OSV.dev

Vendor advisories

  • CVE-2020-27783 Red Hat Product Security624 products fixed · 6 known affected

    python-lxml: mXSS due to the use of improper parser

    python-lxml.src as a component of Red Hat Enterprise Linux 5 · python-lxml.src as a component of Red Hat Enterprise Linux 6 · python-lxml-docs as a component of Red Hat Enterprise Linux 7 · +3 more

  • RHSA-2021:3254 Red Hat Product Security126 products fixed

    Red Hat Security Advisory: rh-python38 security, bug fix, and enhancement update

  • RHSA-2021:1898 Red Hat Product Security13 products fixed

    Red Hat Security Advisory: python-lxml security update

  • RHSA-2021:1879 Red Hat Product Security221 products fixed

    Red Hat Security Advisory: python38:3.8 security update

  • RHSA-2021:1761 Red Hat Product Security264 products fixed

    Red Hat Security Advisory: python27:2.7 security and bug fix update

Full record on NVD

Fix

  1. Vendor fix Red Hat Product Security RHSA-2021:3254 · 126 productsFor details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
  2. No fix planned, says the vendor Red Hat Product Security CVE-2020-27783 · 5 productsOut of support scope
  3. No fix planned, says the vendor Red Hat Product Security CVE-2020-27783 · 1 productWill not fix

Advisories and patches

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
none listed
PoC-in-GitHub

Sources

  • CISA-ADPSSVC decisionnone2025-12-17
  • OpenCVESSVC decisionnone—
  • CISA-ADPCVSS 3.16.12025-12-17
  • NVDCVSS 3.16.1read 2026-10-23
  • NVDCVSS 2.04.3read 2026-10-23
  • CNAweakness (CWE)CWE-79read 2026-10-23
  • NVDweakness (CWE)CWE-79read 2026-10-23
  • FIRST EPSSEPSS score4.0 %2026-10-23
  • OSVaffected packages—

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Published
2020-12-03
Last Modified
2026-06-17
NVD status
Modified

Frequently asked questions

What is CVE-2020-27783?

A XSS vulnerability was discovered in python-lxml's clean module. The module's parser didn't properly imitate browsers, which caused different behaviors between the sanitizer and the user's page. A remote attacker could exploit this flaw to run arbitrary HTML/JS code.

Is CVE-2020-27783 actively exploited?

Active exploitation of CVE-2020-27783 has not been confirmed. Its EPSS score was 4.0% on 2026-10-23, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2020-27783?

CVE-2020-27783 has a CVSS v3 base score of 6.1 (MEDIUM severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N.

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