Vulnerability-Lookup

GHSA-HH8V-HGVP-G3F5

Vulnerability from github – Published: 2026-03-19 19:04 – Updated: 2026-03-27 21:58

Summary

league/commonmark has an embed extension allowed_domains bypass

Details

Impact

The DomainFilteringAdapter in the Embed extension is vulnerable to an allowlist bypass due to a missing hostname boundary assertion in the domain-matching regex. An attacker-controlled domain like youtube.com.evil passes the allowlist check when youtube.com is an allowed domain.

This enables two attack vectors:

SSRF: The OscaroteroEmbedAdapter makes server-side HTTP requests to the embed URL via the embed/embed library. A bypassed domain filter causes the server to make outbound requests to an attacker-controlled host, potentially probing internal services or exfiltrating request metadata.
XSS: EmbedRenderer outputs the oEmbed response HTML directly into the page with no sanitization. An attacker controlling the bypassed domain can return arbitrary HTML/JavaScript in their oEmbed response, which is rendered verbatim.

Any application using the Embed extension and relying on allowed_domains to restrict domains when processing untrusted Markdown input is affected.

Patches

This has been patched in version 2.8.2. The fix replaces the regex-based domain check with explicit hostname parsing using parse_url(), ensuring exact domain and subdomain matching only.

Workarounds

Disable the Embed extension, or restrict its use to trusted users
Provide your own domain-filtering implementation of EmbedAdapterInterface
Enable a Content Security Policy (CSP) and outbound firewall restrictions

Severity

6.3 (Medium)


                  
                    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

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JSON

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{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 2.8.1"
      },
      "package": {
        "ecosystem": "Packagist",
        "name": "league/commonmark"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.3.0"
            },
            {
              "fixed": "2.8.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-33347"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-185",
      "CWE-79",
      "CWE-918"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-03-19T19:04:24Z",
    "nvd_published_at": "2026-03-24T20:16:29Z",
    "severity": "MODERATE"
  },
  "details": "### Impact\n\nThe `DomainFilteringAdapter` in the Embed extension is vulnerable to an allowlist bypass due to a missing hostname boundary assertion in the domain-matching regex. An attacker-controlled domain like `youtube.com.evil` passes the allowlist check when `youtube.com` is an allowed domain.\n\nThis enables two attack vectors:\n\n- **SSRF**: The `OscaroteroEmbedAdapter` makes server-side HTTP requests to the embed URL via the `embed/embed` library. A bypassed domain filter causes the server to make outbound requests to an attacker-controlled host, potentially probing internal services or exfiltrating request metadata.\n- **XSS**: `EmbedRenderer` outputs the oEmbed response HTML directly into the page with no sanitization. An attacker controlling the bypassed domain can return arbitrary HTML/JavaScript in their oEmbed response, which is rendered verbatim.\n\nAny application using the `Embed` extension and relying on `allowed_domains` to restrict domains when processing untrusted Markdown input is affected.\n\n### Patches\n\nThis has been patched in version **2.8.2**. The fix replaces the regex-based domain check with explicit hostname parsing using `parse_url()`, ensuring exact domain and subdomain matching only.\n\n### Workarounds\n\n- Disable the `Embed` extension, or restrict its use to trusted users\n- Provide your own domain-filtering implementation of `EmbedAdapterInterface`\n- Enable a [Content Security Policy (CSP)](https://developer.mozilla.org/en-US/docs/Web/HTTP/CSP) and outbound firewall restrictions",
  "id": "GHSA-hh8v-hgvp-g3f5",
  "modified": "2026-03-27T21:58:03Z",
  "published": "2026-03-19T19:04:24Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/thephpleague/commonmark/security/advisories/GHSA-hh8v-hgvp-g3f5"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-33347"
    },
    {
      "type": "WEB",
      "url": "https://github.com/thephpleague/commonmark/commit/59fb075d2101740c337c7216e3f32b36c204218b"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/thephpleague/commonmark"
    },
    {
      "type": "WEB",
      "url": "https://github.com/thephpleague/commonmark/releases/tag/2.8.2"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "league/commonmark has an embed extension allowed_domains bypass"
}

CVE-2026-33347 (GCVE-0-2026-33347)

Vulnerability from cvelistv5 – Published: 2026-03-24 19:26 – Updated: 2026-03-26 19:52

Title

league/commonmark has an embed extension allowed_domains bypass

Summary

league/commonmark is a PHP Markdown parser. From version 2.3.0 to before version 2.8.2, the DomainFilteringAdapter in the Embed extension is vulnerable to an allowlist bypass due to a missing hostname boundary assertion in the domain-matching regex. An attacker-controlled domain like youtube.com.evil passes the allowlist check when youtube.com is an allowed domain. This issue has been patched in version 2.8.2.

Severity

6.3 (Medium)


                        
                          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

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-03-26 19:34 UTC

CWE

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

Assigner

GitHub_M mitre root Scorecard

References

3 references

URL	Tags
https://github.com/thephpleague/commonmark/securi…	x_refsource_CONFIRM
https://github.com/thephpleague/commonmark/commit…	x_refsource_MISC
https://github.com/thephpleague/commonmark/releas…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version
thephpleague	commonmark	Affected: >= 2.3.0, < 2.8.2

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-33347",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "yes"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-03-26T19:34:18.389527Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-03-26T19:52:12.754Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "commonmark",
          "vendor": "thephpleague",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 2.3.0, \u003c 2.8.2"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "league/commonmark is a PHP Markdown parser. From version 2.3.0 to before version 2.8.2, the DomainFilteringAdapter in the Embed extension is vulnerable to an allowlist bypass due to a missing hostname boundary assertion in the domain-matching regex. An attacker-controlled domain like youtube.com.evil passes the allowlist check when youtube.com is an allowed domain. This issue has been patched in version 2.8.2."
        }
      ],
      "metrics": [
        {
          "cvssV4_0": {
            "attackComplexity": "LOW",
            "attackRequirements": "PRESENT",
            "attackVector": "NETWORK",
            "baseScore": 6.3,
            "baseSeverity": "MEDIUM",
            "privilegesRequired": "NONE",
            "subAvailabilityImpact": "NONE",
            "subConfidentialityImpact": "LOW",
            "subIntegrityImpact": "LOW",
            "userInteraction": "NONE",
            "vectorString": "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",
            "version": "4.0",
            "vulnAvailabilityImpact": "NONE",
            "vulnConfidentialityImpact": "NONE",
            "vulnIntegrityImpact": "LOW"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-79",
              "description": "CWE-79: Improper Neutralization of Input During Web Page Generation (\u0027Cross-site Scripting\u0027)",
              "lang": "en",
              "type": "CWE"
            }
          ]
        },
        {
          "descriptions": [
            {
              "cweId": "CWE-185",
              "description": "CWE-185: Incorrect Regular Expression",
              "lang": "en",
              "type": "CWE"
            }
          ]
        },
        {
          "descriptions": [
            {
              "cweId": "CWE-918",
              "description": "CWE-918: Server-Side Request Forgery (SSRF)",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-03-24T19:26:23.872Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/thephpleague/commonmark/security/advisories/GHSA-hh8v-hgvp-g3f5",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/thephpleague/commonmark/security/advisories/GHSA-hh8v-hgvp-g3f5"
        },
        {
          "name": "https://github.com/thephpleague/commonmark/commit/59fb075d2101740c337c7216e3f32b36c204218b",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/thephpleague/commonmark/commit/59fb075d2101740c337c7216e3f32b36c204218b"
        },
        {
          "name": "https://github.com/thephpleague/commonmark/releases/tag/2.8.2",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/thephpleague/commonmark/releases/tag/2.8.2"
        }
      ],
      "source": {
        "advisory": "GHSA-hh8v-hgvp-g3f5",
        "discovery": "UNKNOWN"
      },
      "title": "league/commonmark has an embed extension allowed_domains bypass"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-33347",
    "datePublished": "2026-03-24T19:26:23.872Z",
    "dateReserved": "2026-03-18T22:15:11.814Z",
    "dateUpdated": "2026-03-26T19:52:12.754Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

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