Vulnerabilities in pkg:pypi/justhtml

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-v7cf-c9rm-wm3j",
  "modified" : "2026-08-25T16:40:34Z",
  "published" : "2026-03-17T14:07:38Z",
  "aliases" : [ "CVE-2026-9769" ],
  "summary" : "Uncontrolled recursion DoS in JustHTML() via deeply nested HTML",
  "details" : "### Summary\n\njusthtml through 1.9.1 allows denial of service via deeply nested HTML. During parsing, `JustHTML.__init__()` always reaches `TreeBuilder.finish()`, which unconditionally calls `_populate_selectedcontent()`. That function recursively traverses the DOM via `_find_elements()` / `_find_element()` without a depth bound, allowing attacker-controlled deeply nested input to trigger an unhandled `RecursionError` on CPython. Depending on the host application's exception handling, this can abort parsing, fail requests, or terminate a worker/process.\n\n### Details\n\n`TreeBuilder.finish()` ([`treebuilder.py#L476`](https://github.com/EmilStenstrom/justhtml/blob/a866b6077770d9ec4cb6b6f9bfe7c918f98455e4/src/justhtml/treebuilder.py#L476)) unconditionally calls `_populate_selectedcontent(self.document)` at [line 494](https://github.com/EmilStenstrom/justhtml/blob/a866b6077770d9ec4cb6b6f9bfe7c918f98455e4/src/justhtml/treebuilder.py#L494). `_populate_selectedcontent()` ([`treebuilder.py#L1243`](https://github.com/EmilStenstrom/justhtml/blob/a866b6077770d9ec4cb6b6f9bfe7c918f98455e4/src/justhtml/treebuilder.py#L1243)) calls `_find_elements()` ([`treebuilder.py#L1280`](https://github.com/EmilStenstrom/justhtml/blob/a866b6077770d9ec4cb6b6f9bfe7c918f98455e4/src/justhtml/treebuilder.py#L1280)) to recursively search the DOM tree for `<select>` elements:\n\n```python\ndef _find_elements(self, node: Any, name: str, result: list[Any]) -> None:\n    \"\"\"Recursively find all elements with given name.\"\"\"\n    if node.name == name:\n        result.append(node)\n    if node.has_child_nodes():\n        for child in node.children:\n            self._find_elements(child, name, result)  # recursive call\n```\n\nWhen the DOM tree depth exceeds CPython's default recursion limit (1000), this raises an unhandled `RecursionError`. The full call path is:\n\n`JustHTML(html)` → `tokenizer.run()` → `tree_builder.finish()` → `_populate_selectedcontent(document)` → `_find_elements(root, \"select\", selects)` (recursive)\n\nDeeply nested DOM trees can be produced by nesting `<div>` tags ~1000 levels deep. On CPython with the default recursion limit, approximately 11 KB of `<div>` nesting is sufficient to trigger the error. The exact depth threshold is environment-dependent (CPython version, recursion limit setting, call stack depth at invocation).\n\nAdditional recursive functions are affected on already-parsed deep trees:\n- `Node.clone_node(deep=True)` ([`node.py#L523`](https://github.com/EmilStenstrom/justhtml/blob/a866b6077770d9ec4cb6b6f9bfe7c918f98455e4/src/justhtml/node.py#L523)) — called during sanitization\n- `_node_to_html()` ([`serialize.py#L580`](https://github.com/EmilStenstrom/justhtml/blob/a866b6077770d9ec4cb6b6f9bfe7c918f98455e4/src/justhtml/serialize.py#L580)) — used by `to_html(pretty=True)`\n- `_to_markdown_walk()` ([`node.py#L817`](https://github.com/EmilStenstrom/justhtml/blob/a866b6077770d9ec4cb6b6f9bfe7c918f98455e4/src/justhtml/node.py#L817)) — used by `to_markdown()`\n\nNote: the library already uses iterative traversal in several comparable functions (e.g., `_node_to_html_compact` at [`serialize.py#L197`](https://github.com/EmilStenstrom/justhtml/blob/a866b6077770d9ec4cb6b6f9bfe7c918f98455e4/src/justhtml/serialize.py#L197), `_to_text_collect` at [`node.py#L161`](https://github.com/EmilStenstrom/justhtml/blob/a866b6077770d9ec4cb6b6f9bfe7c918f98455e4/src/justhtml/node.py#L161), `_is_blocky_element` at [`serialize.py#L405`](https://github.com/EmilStenstrom/justhtml/blob/a866b6077770d9ec4cb6b6f9bfe7c918f98455e4/src/justhtml/serialize.py#L405), `apply_to_children` at [`transforms.py#L1642`](https://github.com/EmilStenstrom/justhtml/blob/a866b6077770d9ec4cb6b6f9bfe7c918f98455e4/src/justhtml/transforms.py#L1642)), demonstrating the correct pattern.\n\n### PoC\n\n```python\nfrom justhtml import JustHTML\n\nhtml = \"<div>\" * 1000 + \"x\" + \"</div>\" * 1000\ndoc = JustHTML(html)  # raises RecursionError\n```\n\nTest environment: CPython 3.14.3, macOS ARM64 (Apple Silicon), justhtml 1.9.1, default recursion limit (1000)\n\n| Input | Size | Result |\n|-------|------|--------|\n| `<div>` × 500 | 5,501 bytes | OK |\n| `<div>` × 800 | 8,801 bytes | OK |\n| `<div>` × 1000 | 11,001 bytes | RecursionError |\n\nThe error occurs with both `sanitize=True` (default) and `sanitize=False`.\n\n### Impact\n\nAn attacker who can supply HTML for parsing can trigger an unhandled `RecursionError` during `JustHTML()` construction. The error is triggered during construction and is not avoided by `justhtml` configuration alone; mitigating it requires host-application exception handling or input constraints. Depending on the host application's exception handling, this can abort parsing, fail requests, or terminate a worker/process.\n\n### Suggested Fix\n\nConvert the recursive tree traversal functions to iterative implementations using an explicit stack. Example for `_find_elements`:\n\n```python\ndef _find_elements(self, node: Any, name: str, result: list[Any]) -> None:\n    stack = [node]\n    while stack:\n        current = stack.pop()\n        if current.name == name:\n            result.append(current)\n        if current.has_child_nodes():\n            stack.extend(reversed(current.children))\n```\n\nThe same conversion should be applied to `_find_element`, `clone_node(deep=True)`, `_node_to_html()`, and `_to_markdown_walk()`.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "justhtml"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.10.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 1.9.1"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/EmilStenstrom/justhtml/security/advisories/GHSA-v7cf-c9rm-wm3j"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-9769"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/EmilStenstrom/justhtml"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/EmilStenstrom/justhtml/releases/tag/v1.10.0"
  }, {
    "type" : "WEB",
    "url" : "https://www.vulncheck.com/advisories/justhtml-before-denial-of-service-via-deeply-nested-html"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-674" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-17T14:07:38Z",
    "nvd_published_at" : null
  }
}