How severe is CVE-2026-30838?

CVE-2026-30838 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-2026-30838 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (12th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-30838?

CVE-2026-30838 affects Thephpleague Commonmark. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-30838?

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

Does CVE-2026-30838 have an EU (EUVD) identifier?

Yes. CVE-2026-30838 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-10168.

When was CVE-2026-30838 published?

CVE-2026-30838 was published on 2026-03-07 and last updated on 2026-06-17.

CVE-2026-30838

CVE-2026-30838 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 v4: 5.1
EPSS exploit prediction: 0% (12th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-10168
Weakness: CWE-79
Affected product: Thephpleague Commonmark
Published: 2026-03-07
Last modified: 2026-06-17

Description

league/commonmark is a PHP Markdown parser. Prior to version 2.8.1, the DisallowedRawHtml extension can be bypassed by inserting a newline, tab, or other ASCII whitespace character between a disallowed HTML tag name and the closing >. For example, <script\n> would pass through unfiltered and be rendered as a valid HTML tag by browsers. This is a cross-site scripting (XSS) vector for any application that relies on this extension to sanitize untrusted user input. All applications using the DisallowedRawHtml extension to process untrusted markdown are affected. Applications that use a dedicated HTML sanitizer (such as HTML Purifier) on the rendered output are not affected. This issue has been patched in version 2.8.1.

Frequently asked questions

What is CVE-2026-30838?: league/commonmark is a PHP Markdown parser. Prior to version 2.8.1, the DisallowedRawHtml extension can be bypassed by inserting a newline, tab, or other ASCII whitespace character between a disallowed HTML tag name and the closing >. For example, <script\n> would pass through unfiltered and be rendered as a valid HTML tag by browsers. This is a cross-site scripting (XSS) vector for any application that relies on this extension to sanitize untrusted user input. All applications using the DisallowedRawHtml extension to process untrusted markdown are affected. Applications that use a dedicated HTML sanitizer (such as HTML Purifier) on the rendered output are not affected. This issue has been patched in version 2.8.1.
How severe is CVE-2026-30838?: CVE-2026-30838 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-2026-30838 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (12th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-30838?: CVE-2026-30838 affects Thephpleague Commonmark. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-30838?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-30838 have an EU (EUVD) identifier?: Yes. CVE-2026-30838 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-10168.
When was CVE-2026-30838 published?: CVE-2026-30838 was published on 2026-03-07 and last updated on 2026-06-17.

References

https://github.com/thephpleague/commonmark/security/advisories/GHSA-4v6x-c7xx-hw9f

Affected products (1)

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

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