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Vulnerability record · CVE-2018-20583 · published 30 December 2018

CVE-2018-20583: Thephpleague commonmark cross-site scripting vulnerability

Thephpleague · Commonmark

Cross-site scripting (XSS) vulnerability in the PHP League CommonMark library versions 0.15.6 through 0.18.x before 0.18.1 allows remote attackers to insert unsafe URLs into HTML (even if allow_unsafe_links is false) via a newline character (e.g., writing javascript as javascri%0apt).

6.1 CVSS 3.0 Medium EPSS 1.6% · top 25.2% CWE-79 · Cross-site scripting
6.1CVSS 3.0 base score, v2 4.3
1.6%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
6References, 2 tagged exploit
17 Jun 2026Last modified by NVD

Description

Cross-site scripting (XSS) vulnerability in the PHP League CommonMark library versions 0.15.6 through 0.18.x before 0.18.1 allows remote attackers to insert unsafe URLs into HTML (even if allow_unsafe_links is false) via a newline character (e.g., writing javascript as javascri%0apt).

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

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://commonmark.thephpleague.com/changelog/ Release NotesThird Party Advisory
https://github.com/thephpleague/commonmark/issues/337 ExploitThird Party Advisory
https://github.com/thephpleague/commonmark/releases/tag/0.18.1 Release NotesThird Party Advisory
https://commonmark.thephpleague.com/changelog/ Release NotesThird Party Advisory
https://github.com/thephpleague/commonmark/issues/337 ExploitThird Party Advisory
https://github.com/thephpleague/commonmark/releases/tag/0.18.1 Release NotesThird Party Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2018-20583), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.