CVE-2026-33347Network attack vector

SSRF and XSS via hostname allowlist bypass

Published Mar 24, 2026 · Updated Mar 24, 2026

SSRF and XSS in the Embed extension of The PHP League CommonMark 2.3.0 through 2.8.1 allow remote attackers to abuse crafted URLs. DomainFilteringAdapter's regex accepts hostnames such as youtube.com.evil for an allowed youtube.com suffix, after which OscaroteroEmbedAdapter fetches the URL and EmbedRenderer emits returned HTML without sanitization. Exploitation requires an application to process untrusted Markdown with Embed and allowed_domains enabled; it permits server-side requests to attacker-controlled hosts and script execution in rendered pages.

CVSS severity6.3
Medium
EPSS probability0.24%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

SSRF and XSS in the Embed extension of The PHP League CommonMark 2.3.0 through 2.8.1 allow remote attackers to abuse crafted URLs. DomainFilteringAdapter's regex accepts hostnames such as youtube.com.evil for an allowed youtube.com suffix, after which OscaroteroEmbedAdapter fetches the URL and EmbedRenderer emits returned HTML without sanitization. Exploitation requires an application to process untrusted Markdown with Embed and allowed_domains enabled; it permits server-side requests to attacker-controlled hosts and script execution in rendered pages.

The record

CVE
CVE-2026-33347
Published
Mar 24, 2026
Updated
Mar 24, 2026
Vendor
The PHP League
Product
CommonMark
Classifications
CWE-79, CWE-185, CWE-918
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 24, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 24, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>= 2.3.0, < 2.8.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The PHP League · CommonMarkversion=>= 2.3.0, < 2.8.2

Published CVSS scores

6.3GitHub, Inc.CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N
6.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
CWE-185Incorrect Regular Expression
CWE-918Server-Side Request Forgery (SSRF)

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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