How severe is CVE-2018-20583?

CVE-2018-20583 has a CVSS 3.x base score of 6.1, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.

Is CVE-2018-20583 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (73rd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2018-20583?

CVE-2018-20583 affects Thephpleague Commonmark. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2018-20583?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2018-20583 published?

CVE-2018-20583 was published on 2018-12-30 and last updated on 2026-06-17.

CVE-2018-20583

CVE-2018-20583 is a medium-severity vulnerability in Thephpleague Commonmark with a CVSS 3.x base score of 6.1. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-79.

Key facts

Severity: Medium (CVSS 3.x base score 6.1)
CVSS v2: 4.3
EPSS exploit prediction: 2% (73rd percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-79
Affected product: Thephpleague Commonmark
Published: 2018-12-30
Last modified: 2026-06-17

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).

Frequently asked questions

What is CVE-2018-20583?: 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).
How severe is CVE-2018-20583?: CVE-2018-20583 has a CVSS 3.x base score of 6.1, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2018-20583 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (73rd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2018-20583?: CVE-2018-20583 affects Thephpleague Commonmark. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2018-20583?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2018-20583 published?: CVE-2018-20583 was published on 2018-12-30 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:thephpleague:commonmark:*:*:*:*:*:*:*:*

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