{"id":"CVE-2026-59927","aliases":["DEBIAN-CVE-2026-59927","EUVD-2026-42339","GHSA-8mpj-m6qm-5qr8","PYSEC-2026-2215","SUSE-SU-2026:22655-1","UBUNTU-CVE-2026-59927","openSUSE-SU-2026:21339-1"],"status":"published","title":"Mistune directives/include: mutual `.. include::` recursion crashes the renderer with `RecursionError`, denial of service via two attacker-controlled markdown files","description":"Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, the Include directive in src/mistune/directives/include.py detects only direct self-includes and not indirect cycles, allowing two markdown files that include each other to trigger unbounded recursion, raise RecursionError, and crash the rendering request. This issue is fixed in version 3.3.0.","severity":{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-10","score":0.00529,"percentile":0.45097,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-674","CWE-755"],"published":"2026-07-08T16:24:37Z","modified":"2026-10-28T02:30:30Z","fixes":[{"ecosystem":"PyPI","package":"mistune","fixed_in":["3.3.0"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"PyPI","package":"mistune","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.3.0"}]}]},{"source":"osv","ecosystem":"Debian:12","package":"mistune","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.0.4-1","2.0.4-2","3.0.2-1","3.0.2-2","3.1.3-1","3.1.4-1","3.3.4-1","3.4.0-1"]},{"source":"osv","ecosystem":"Debian:13","package":"mistune","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.1.3-1","3.1.4-1","3.3.4-1","3.4.0-1"]},{"source":"osv","ecosystem":"Debian:14","package":"mistune","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.1.3-1","3.1.4-1","3.3.4-1","3.4.0-1"]},{"source":"osv","ecosystem":"PyPI","package":"mistune","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.3.0"}]}],"versions":["0.1.0","0.2.0","0.3.0","0.3.1","0.4","0.4.1","0.5","0.5.1","0.6","0.7","0.7.1","0.7.2","0.7.3","0.7.4","0.8","0.8.1","0.8.2","0.8.3","0.8.4","2.0.0","2.0.0a1","2.0.0a2","2.0.0a3","2.0.0a4","2.0.0a5","2.0.0a6","2.0.0rc1","2.0.1","2.0.2","2.0.3","2.0.4","2.0.5","2.1.0","3.0.0","3.0.0a1","3.0.0a2","3.0.0a3","3.0.0rc1","3.0.0rc2","3.0.0rc3","3.0.0rc4","3.0.0rc5","3.0.1","3.0.2","3.1.0","3.1.1","3.1.2","3.1.3","3.1.4","3.2.0","3.2.1"]},{"source":"osv","ecosystem":"PyPI","package":"mistune","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.3.0"}]}],"versions":["0.1.0","0.2.0","0.3.0","0.3.1","0.4","0.4.1","0.5","0.5.1","0.6","0.7","0.7.1","0.7.2","0.7.3","0.7.4","0.8","0.8.1","0.8.2","0.8.3","0.8.4","2.0.0","2.0.0a1","2.0.0a2","2.0.0a3","2.0.0a4","2.0.0a5","2.0.0a6","2.0.0rc1","2.0.1","2.0.2","2.0.3","2.0.4","2.0.5","2.1.0","3.0.0","3.0.0a1","3.0.0a2","3.0.0a3","3.0.0rc1","3.0.0rc2","3.0.0rc3","3.0.0rc4","3.0.0rc5","3.0.1","3.0.2","3.1.0","3.1.1","3.1.2","3.1.3","3.1.4","3.2.0","3.2.1"]},{"source":"osv","ecosystem":"SUSE:Linux Enterprise Server 16.0","package":"python-mistune","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.1.3-160000.5.1"}]}],"bundled":10},{"source":"osv","ecosystem":"SUSE:Linux Enterprise Server for SAP applications 16.0","package":"python-mistune","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.1.3-160000.5.1"}]}],"bundled":10},{"source":"osv","ecosystem":"Ubuntu:16.04:LTS","package":"mistune","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.6-2","0.7.1-1"]},{"source":"osv","ecosystem":"Ubuntu:18.04:LTS","package":"mistune","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.7.4-1","0.8-1","0.8.1-1","0.8.3-2"]},{"source":"osv","ecosystem":"Ubuntu:20.04:LTS","package":"mistune","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.8.4-1","0.8.4-2"]},{"source":"osv","ecosystem":"Ubuntu:22.04:LTS","package":"mistune","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.8.4-4","0.8.4-5","2.0.0-1+really0.8.4-1"]},{"source":"osv","ecosystem":"Ubuntu:24.04:LTS","package":"mistune","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.0.4-2","3.0.2-1"]},{"source":"osv","ecosystem":"Ubuntu:25.10","package":"mistune","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.0.2-2","3.1.3-1"]},{"source":"osv","ecosystem":"Ubuntu:26.10","package":"mistune","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.1.4-1"]},{"source":"osv","ecosystem":"Ubuntu:26.04:LTS","package":"mistune","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.1.3-1","3.1.4-1"]},{"source":"osv","ecosystem":"openSUSE:Leap 16.0","package":"python-mistune","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.1.3-160000.5.1"}]}],"bundled":10}],"products":[{"vendor":"lepture","product":"mistune"},{"vendor":"mistune_project","product":"mistune"}],"references":[{"url":"https://github.com/lepture/mistune/security/advisories/GHSA-8mpj-m6qm-5qr8","tags":["x_refsource_CONFIRM","Exploit","Third Party Advisory","advisory","web","evidence","report"]},{"url":"https://github.com/lepture/mistune/commit/1bef343ade163fc3bb95572b15be720084cdb993","tags":["x_refsource_MISC","Patch","fix","web"]},{"url":"https://github.com/lepture/mistune/releases/tag/v3.3.0","tags":["x_refsource_MISC","Release Notes","web","advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-59927","tags":["advisory"]},{"url":"https://github.com/pypa/advisory-database/tree/main/vulns/mistune/PYSEC-2026-2215.yaml","tags":["web"]},{"url":"https://github.com/advisories/GHSA-8mpj-m6qm-5qr8"},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/59xxx/CVE-2026-59927.json","tags":["advisory"]},{"url":"https://security-tracker.debian.org/tracker/CVE-2026-59927","tags":["advisory"]},{"url":"https://github.com/lepture/mistune","tags":["package"]},{"url":"https://www.suse.com/support/update/announcement/2026/suse-su-202622655-1/","tags":["advisory"]},{"url":"https://bugzilla.suse.com/1271082","tags":["report"]},{"url":"https://bugzilla.suse.com/1271117","tags":["report"]},{"url":"https://bugzilla.suse.com/1271119","tags":["report"]},{"url":"https://bugzilla.suse.com/1271121","tags":["report"]},{"url":"https://bugzilla.suse.com/1271125","tags":["report"]},{"url":"https://bugzilla.suse.com/1271127","tags":["report"]},{"url":"https://bugzilla.suse.com/1271128","tags":["report"]},{"url":"https://bugzilla.suse.com/1271131","tags":["report"]},{"url":"https://bugzilla.suse.com/1271132","tags":["report"]},{"url":"https://www.suse.com/security/cve/CVE-2026-44896","tags":["web"]},{"url":"https://www.suse.com/security/cve/CVE-2026-59922","tags":["web"]},{"url":"https://www.suse.com/security/cve/CVE-2026-59923","tags":["web"]},{"url":"https://www.suse.com/security/cve/CVE-2026-59924","tags":["web"]},{"url":"https://www.suse.com/security/cve/CVE-2026-59925","tags":["web"]},{"url":"https://www.suse.com/security/cve/CVE-2026-59926","tags":["web"]},{"url":"https://www.suse.com/security/cve/CVE-2026-59927","tags":["web"]},{"url":"https://www.suse.com/security/cve/CVE-2026-59928","tags":["web"]},{"url":"https://www.suse.com/security/cve/CVE-2026-59929","tags":["web"]},{"url":"https://www.suse.com/security/cve/CVE-2026-59930","tags":["web"]},{"url":"https://ubuntu.com/security/CVE-2026-59927","tags":["report"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-59927","tags":["report"]},{"url":"","tags":["advisory"]}],"sources":{"cve":[{"id":"CVE-2026-59927","title":"Mistune directives/include: mutual `.. include::` recursion crashes the renderer with `RecursionError`, denial of service via two attacker-controlled markdown files","description":"Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, the Include directive in src/mistune/directives/include.py detects only direct self-includes and not indirect cycles, allowing two markdown files that include each other to trigger unbounded recursion, raise RecursionError, and crash the rendering request. This issue is fixed in version 3.3.0.","status":"published","published":"2026-07-08T16:24:37.985Z","modified":"2026-07-08T19:45:20.799Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium","assessor":"cna"}],"cwes":["CWE-674","CWE-755"],"updated_at":"2026-11-02T14:19:58.560602Z"}],"euvd":[{"id":"EUVD-2026-42339","description":"Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, the Include directive in src/mistune/directives/include.py detects only direct self-includes and not indirect cycles, allowing two markdown files that include each other to trigger unbounded recursion, raise RecursionError, and crash the rendering request. This issue is fixed in version 3.3.0.","status":"published","published":"2026-07-08T16:24:37Z","modified":"2026-07-08T19:45:20Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium"}],"updated_at":"2026-11-02T18:20:10.095263Z"}],"ghsa":[{"id":"GHSA-8mpj-m6qm-5qr8","title":"Mistune directives/include: mutual `.. include::` recursion crashes the renderer with `RecursionError`, denial of service via two attacker-controlled markdown files","description":"## Summary\n\n**Type:** Uncontrolled recursion via mutual include. The `Include` directive checks for direct self-reference (`a.md` cannot include `a.md`), but does not detect indirect cycles. Two markdown files that include each other (`a.md` → includes `b.md` → includes `a.md`) cause unbounded recursion until Python's stack limit fires `RecursionError`. The exception propagates out of the renderer and crashes the calling code.\n**File:** `src/mistune/directives/include.py`, lines 33-37 (the self-include check is the only cycle-detection logic).\n**Root cause:** the include logic only compares `os.path.abspath(dest) == os.path.abspath(source_file)`. There is no per-render set of \"files already included\" that would catch transitive cycles. When `a.md` includes `b.md`, the recursive `block.parse(new_state)` call uses `dest` (b.md) as the new `__file__`, which then includes `a.md` (passing the self-check, because the immediate parent file is `b.md`, not `a.md`), which then includes `b.md`, and so on. Each recursion level adds Python frames; the default stack limit of 1000 frames trips after ~7-10 cycle iterations and Python raises `RecursionError`. Since the directive does not catch the exception, it propagates out of `Markdown.parse()` and surfaces in the calling code, crashing the request.\n\n## Affected Code\n\n**File:** `src/mistune/directives/include.py`, lines 28-54.\n\n```python\nrelpath = self.parse_title(m)\ndest = os.path.join(os.path.dirname(source_file), relpath)\ndest = os.path.normpath(dest)\n\nif os.path.abspath(dest) == os.path.abspath(source_file):       # \u003c-- only catches direct self-include\n    return {\"type\": \"block_error\", \"raw\": \"Could not include self: \" + relpath}\n\nif not os.path.isfile(dest):\n    return {\"type\": \"block_error\", \"raw\": \"Could not find file: \" + relpath}\n\nwith open(dest, \"rb\") as f:\n    content = f.read().decode(encoding)\n\next = os.path.splitext(relpath)[1]\nif ext in {\".md\", \".markdown\", \".mkd\"}:\n    new_state = block.state_cls()\n    new_state.env[\"__file__\"] = dest\n    new_state.process(content)\n    block.parse(new_state)                                       # \u003c-- recursive parse, no cycle tracking\n    return new_state.tokens\n```\n\n**Why it's wrong:** the cycle-detection check is one level deep. Multi-file cycles slip through trivially. Python's default recursion limit is 1000 frames, so a cycle of length 2 trips after a few hundred mutual includes; the exception is uncaught by the directive, propagating out of `Markdown.__call__()` and crashing whatever called it.\n\n## Exploit Chain\n\n1. Application uses mistune with the `Include` directive enabled. Application accepts user-supplied markdown files (CMS, wiki, multi-user documentation platform, note-taking app, CI/CD doc renderer).\n2. Attacker uploads two markdown files:\n   - `a.md`: `.. include:: b.md`\n   - `b.md`: `.. include:: a.md`\n3. Renderer is invoked on `a.md` (or any markdown that references this pair). `Include` directive includes `b.md`, which includes `a.md`, which includes `b.md`, ... Each recursion adds Python frames.\n4. After ~340 cycle iterations (depending on default `sys.setrecursionlimit(1000)` and the per-include frame depth), Python raises `RecursionError: maximum recursion depth exceeded`.\n5. The exception is not caught by the directive. It propagates through `block.parse`, through `Markdown.__call__`, and into the application's request handler. If the application doesn't catch it explicitly, the request errors out (HTTP 500 in web contexts, crash in CLI tools).\n\n## Security Impact\n\n**Attacker capability:** crash the rendering engine on demand by submitting any markdown that triggers the cycle. Repeated requests deny service. If the renderer is used in a hot path (per-page-view docs rendering, search-index regeneration, scheduled doc-export jobs), the cycle persists across the whole pipeline.\n**Preconditions:** application uses mistune with the `Include` directive enabled and renders user-supplied markdown that can reference other user-uploaded files. Attacker needs write access to two .md files in the include search path (or a single file including a known-recurring pair).\n**Differential:** PoC-verified against mistune@3.2.1:\n\n```python\nimport os, mistune\nfrom mistune.directives import RSTDirective, Include\n\nos.makedirs('/tmp/mistune-recur', exist_ok=True)\nwith open('/tmp/mistune-recur/a.md', 'w') as f:\n    f.write('A\\n\\n.. include:: b.md')\nwith open('/tmp/mistune-recur/b.md', 'w') as f:\n    f.write('B\\n\\n.. include:: a.md')\n\nmd = mistune.create_markdown(plugins=[RSTDirective([Include()])])\nstate = md.block.state_cls()\nstate.env['__file__'] = '/tmp/mistune-recur/a.md'\nmd.parse('.. include:: b.md', state=state)\n# RecursionError: maximum recursion depth exceeded\n```\n\nThe patched build (with the suggested fix below) returns a `block_error` token like the existing self-include check, instead of recursing forever.\n\n## Suggested Fix\n\nTrack included paths in `state.env` and reject any include that would re-enter a path already on the include stack:\n\n```diff\n--- a/src/mistune/directives/include.py\n+++ b/src/mistune/directives/include.py\n@@ -28,8 +28,18 @@ class Include(DirectivePlugin):\n         relpath = self.parse_title(m)\n-        dest = os.path.join(os.path.dirname(source_file), relpath)\n-        dest = os.path.normpath(dest)\n+        base = os.path.realpath(os.path.dirname(source_file))\n+        dest = os.path.realpath(os.path.join(base, relpath))\n+\n+        # Track include stack across recursive parses to detect cycles.\n+        include_stack = state.env.setdefault(\"__include_stack__\", [])\n+        if dest in include_stack or dest == os.path.realpath(source_file):\n+            return {\n+                \"type\": \"block_error\",\n+                \"raw\": \"Could not include (cycle): \" + relpath,\n+            }\n\n-        if os.path.abspath(dest) == os.path.abspath(source_file):\n-            return {\n-                \"type\": \"block_error\",\n-                \"raw\": \"Could not include self: \" + relpath,\n-            }\n@@ ... in the markdown-include branch ...\n+        include_stack.append(dest)\n+        try:\n+            new_state = block.state_cls()\n+            new_state.env[\"__file__\"] = dest\n+            new_state.env[\"__include_stack__\"] = include_stack\n+            new_state.process(content)\n+            block.parse(new_state)\n+            return new_state.tokens\n+        finally:\n+            include_stack.pop()\n```\n\nThis catches cycles of any length (`a → b → a`, `a → b → c → a`, etc.). Pair this with the path-containment fix from the LFI advisory and the HTML-extension fix from the include-XSS advisory; together those three patches make the `Include` directive safe to enable on user-supplied markdown.\n\nAdd a regression test asserting that a 2-cycle and a 3-cycle both produce `block_error` rather than `RecursionError`.","status":"published","published":"2026-07-20T21:24:42Z","modified":"2026-07-20T21:24:43Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium"}],"cwes":["CWE-674","CWE-755"],"updated_at":"2026-11-02T14:40:48.410776Z"}],"nvd":[{"id":"CVE-2026-59927","description":"Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, the Include directive in src/mistune/directives/include.py detects only direct self-includes and not indirect cycles, allowing two markdown files that include each other to trigger unbounded recursion, raise RecursionError, and crash the rendering request. This issue is fixed in version 3.3.0.","status":"published","published":"2026-07-08T17:17:28.45Z","modified":"2026-10-25T17:10:00.197Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium","assessor":"secondary"}],"cwes":["CWE-674","CWE-755"],"updated_at":"2026-11-02T14:12:28.4135Z"}],"osv":[{"id":"CVE-2026-59927","title":"Mistune directives/include: mutual `.. include::` recursion crashes the renderer with `RecursionError`, denial of service via two attacker-controlled markdown files","description":"Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, the Include directive in src/mistune/directives/include.py detects only direct self-includes and not indirect cycles, allowing two markdown files that include each other to trigger unbounded recursion, raise RecursionError, and crash the rendering request. This issue is fixed in version 3.3.0.","status":"published","published":"2026-07-08T16:24:37.985Z","modified":"2026-10-28T02:30:30.712004504Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium"}],"cwes":["CWE-674","CWE-755"],"updated_at":"2026-11-02T15:45:12.496548Z"},{"id":"DEBIAN-CVE-2026-59927","description":"Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, the Include directive in src/mistune/directives/include.py detects only direct self-includes and not indirect cycles, allowing two markdown files that include each other to trigger unbounded recursion, raise RecursionError, and crash the rendering request. This issue is fixed in version 3.3.0.","status":"published","published":"2026-07-08T17:17:28.45Z","modified":"2026-10-26T12:02:58.467372897Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium"}],"updated_at":"2026-11-02T15:45:57.932517Z"},{"id":"GHSA-8mpj-m6qm-5qr8","title":"Mistune directives/include: mutual `.. include::` recursion crashes the renderer with `RecursionError`, denial of service via two attacker-controlled markdown files","description":"## Summary\n\n**Type:** Uncontrolled recursion via mutual include. The `Include` directive checks for direct self-reference (`a.md` cannot include `a.md`), but does not detect indirect cycles. Two markdown files that include each other (`a.md` → includes `b.md` → includes `a.md`) cause unbounded recursion until Python's stack limit fires `RecursionError`. The exception propagates out of the renderer and crashes the calling code.\n**File:** `src/mistune/directives/include.py`, lines 33-37 (the self-include check is the only cycle-detection logic).\n**Root cause:** the include logic only compares `os.path.abspath(dest) == os.path.abspath(source_file)`. There is no per-render set of \"files already included\" that would catch transitive cycles. When `a.md` includes `b.md`, the recursive `block.parse(new_state)` call uses `dest` (b.md) as the new `__file__`, which then includes `a.md` (passing the self-check, because the immediate parent file is `b.md`, not `a.md`), which then includes `b.md`, and so on. Each recursion level adds Python frames; the default stack limit of 1000 frames trips after ~7-10 cycle iterations and Python raises `RecursionError`. Since the directive does not catch the exception, it propagates out of `Markdown.parse()` and surfaces in the calling code, crashing the request.\n\n## Affected Code\n\n**File:** `src/mistune/directives/include.py`, lines 28-54.\n\n```python\nrelpath = self.parse_title(m)\ndest = os.path.join(os.path.dirname(source_file), relpath)\ndest = os.path.normpath(dest)\n\nif os.path.abspath(dest) == os.path.abspath(source_file):       # \u003c-- only catches direct self-include\n    return {\"type\": \"block_error\", \"raw\": \"Could not include self: \" + relpath}\n\nif not os.path.isfile(dest):\n    return {\"type\": \"block_error\", \"raw\": \"Could not find file: \" + relpath}\n\nwith open(dest, \"rb\") as f:\n    content = f.read().decode(encoding)\n\next = os.path.splitext(relpath)[1]\nif ext in {\".md\", \".markdown\", \".mkd\"}:\n    new_state = block.state_cls()\n    new_state.env[\"__file__\"] = dest\n    new_state.process(content)\n    block.parse(new_state)                                       # \u003c-- recursive parse, no cycle tracking\n    return new_state.tokens\n```\n\n**Why it's wrong:** the cycle-detection check is one level deep. Multi-file cycles slip through trivially. Python's default recursion limit is 1000 frames, so a cycle of length 2 trips after a few hundred mutual includes; the exception is uncaught by the directive, propagating out of `Markdown.__call__()` and crashing whatever called it.\n\n## Exploit Chain\n\n1. Application uses mistune with the `Include` directive enabled. Application accepts user-supplied markdown files (CMS, wiki, multi-user documentation platform, note-taking app, CI/CD doc renderer).\n2. Attacker uploads two markdown files:\n   - `a.md`: `.. include:: b.md`\n   - `b.md`: `.. include:: a.md`\n3. Renderer is invoked on `a.md` (or any markdown that references this pair). `Include` directive includes `b.md`, which includes `a.md`, which includes `b.md`, ... Each recursion adds Python frames.\n4. After ~340 cycle iterations (depending on default `sys.setrecursionlimit(1000)` and the per-include frame depth), Python raises `RecursionError: maximum recursion depth exceeded`.\n5. The exception is not caught by the directive. It propagates through `block.parse`, through `Markdown.__call__`, and into the application's request handler. If the application doesn't catch it explicitly, the request errors out (HTTP 500 in web contexts, crash in CLI tools).\n\n## Security Impact\n\n**Attacker capability:** crash the rendering engine on demand by submitting any markdown that triggers the cycle. Repeated requests deny service. If the renderer is used in a hot path (per-page-view docs rendering, search-index regeneration, scheduled doc-export jobs), the cycle persists across the whole pipeline.\n**Preconditions:** application uses mistune with the `Include` directive enabled and renders user-supplied markdown that can reference other user-uploaded files. Attacker needs write access to two .md files in the include search path (or a single file including a known-recurring pair).\n**Differential:** PoC-verified against mistune@3.2.1:\n\n```python\nimport os, mistune\nfrom mistune.directives import RSTDirective, Include\n\nos.makedirs('/tmp/mistune-recur', exist_ok=True)\nwith open('/tmp/mistune-recur/a.md', 'w') as f:\n    f.write('A\\n\\n.. include:: b.md')\nwith open('/tmp/mistune-recur/b.md', 'w') as f:\n    f.write('B\\n\\n.. include:: a.md')\n\nmd = mistune.create_markdown(plugins=[RSTDirective([Include()])])\nstate = md.block.state_cls()\nstate.env['__file__'] = '/tmp/mistune-recur/a.md'\nmd.parse('.. include:: b.md', state=state)\n# RecursionError: maximum recursion depth exceeded\n```\n\nThe patched build (with the suggested fix below) returns a `block_error` token like the existing self-include check, instead of recursing forever.\n\n## Suggested Fix\n\nTrack included paths in `state.env` and reject any include that would re-enter a path already on the include stack:\n\n```diff\n--- a/src/mistune/directives/include.py\n+++ b/src/mistune/directives/include.py\n@@ -28,8 +28,18 @@ class Include(DirectivePlugin):\n         relpath = self.parse_title(m)\n-        dest = os.path.join(os.path.dirname(source_file), relpath)\n-        dest = os.path.normpath(dest)\n+        base = os.path.realpath(os.path.dirname(source_file))\n+        dest = os.path.realpath(os.path.join(base, relpath))\n+\n+        # Track include stack across recursive parses to detect cycles.\n+        include_stack = state.env.setdefault(\"__include_stack__\", [])\n+        if dest in include_stack or dest == os.path.realpath(source_file):\n+            return {\n+                \"type\": \"block_error\",\n+                \"raw\": \"Could not include (cycle): \" + relpath,\n+            }\n\n-        if os.path.abspath(dest) == os.path.abspath(source_file):\n-            return {\n-                \"type\": \"block_error\",\n-                \"raw\": \"Could not include self: \" + relpath,\n-            }\n@@ ... in the markdown-include branch ...\n+        include_stack.append(dest)\n+        try:\n+            new_state = block.state_cls()\n+            new_state.env[\"__file__\"] = dest\n+            new_state.env[\"__include_stack__\"] = include_stack\n+            new_state.process(content)\n+            block.parse(new_state)\n+            return new_state.tokens\n+        finally:\n+            include_stack.pop()\n```\n\nThis catches cycles of any length (`a → b → a`, `a → b → c → a`, etc.). Pair this with the path-containment fix from the LFI advisory and the HTML-extension fix from the include-XSS advisory; together those three patches make the `Include` directive safe to enable on user-supplied markdown.\n\nAdd a regression test asserting that a 2-cycle and a 3-cycle both produce `block_error` rather than `RecursionError`.","status":"published","published":"2026-07-20T21:24:42Z","modified":"2026-07-20T21:30:45.969881443Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium"}],"cwes":["CWE-674","CWE-755"],"updated_at":"2026-11-02T15:46:42.437513Z"},{"id":"PYSEC-2026-2215","description":"Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, the Include directive in src/mistune/directives/include.py detects only direct self-includes and not indirect cycles, allowing two markdown files that include each other to trigger unbounded recursion, raise RecursionError, and crash the rendering request. This issue is fixed in version 3.3.0.","status":"published","published":"2026-07-08T17:17:28.45Z","modified":"2026-07-13T07:15:18.817354531Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium"}],"updated_at":"2026-11-02T15:52:55.537808Z"},{"id":"UBUNTU-CVE-2026-59927","description":"Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, the Include directive in src/mistune/directives/include.py detects only direct self-includes and not indirect cycles, allowing two markdown files that include each other to trigger unbounded recursion, raise RecursionError, and crash the rendering request. This issue is fixed in version 3.3.0.","status":"published","published":"2026-07-08T17:17:00Z","modified":"2026-10-17T12:57:17.704222379Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium"}],"updated_at":"2026-11-02T16:56:41.911783Z"},{"id":"openSUSE-SU-2026:21339-1","title":"Security update for python-mistune","description":"This update for python-mistune fixes the following issues\n\n- CVE-2026-59922: quadratic-time parsing on long runs of some markers in `formatting.py` can lead to DoS (bsc#1271117).\n- CVE-2026-59923: `HTMLRenderer.safe_url()` does not block percent-encoded javascript URIs and allows for XSS\n  (bsc#1271119).\n- CVE-2026-59924: improper processing of user-supplied include paths in `Include.parse()` can lead to path traversal\n  and arbitrary file reads (bsc#1271121).\n- CVE-2026-59925: quadratic-time parsing on long runs of some emphasis pairs in `inline_parser` can lead to DoS\n  (bsc#1271125).\n- CVE-2026-59926: improper escaping in `render_admonition()` can lead to atribute injection and XSS (bsc#1271127).\n- CVE-2026-59927: uncontrolled recursion when processing two markdown files that include each other can lead to a DoS\n   (bsc#1271128).\n- CVE-2026-59928: quadratic-time parsing on long lists of repeated reference-link definitions in `block_parser` can\n  lead to DoS (bsc#1271131).\n- CVE-2026-59929: HARMFUL_PROTOCOLS list misses legacy and chained schemes and allow arbitrary script execution in\n  user agents (bsc#1271132).\n- CVE-2026-59930: the `toc` plugin and `TableOfContents` directive generate heading IDs with predictable values and\n  allow for collisions with attacker-controlled `id=\"toc_N\"` content (bsc#1271082).\n","status":"published","published":"2026-07-14T10:41:18Z","modified":"2026-07-15T10:00:11.548963212Z","updated_at":"2026-11-02T16:58:41.885092Z"},{"id":"SUSE-SU-2026:22655-1","title":"Security update for python-mistune","description":"This update for python-mistune fixes the following issues\n\n- CVE-2026-59922: quadratic-time parsing on long runs of some markers in `formatting.py` can lead to DoS (bsc#1271117).\n- CVE-2026-59923: `HTMLRenderer.safe_url()` does not block percent-encoded javascript URIs and allows for XSS\n  (bsc#1271119).\n- CVE-2026-59924: improper processing of user-supplied include paths in `Include.parse()` can lead to path traversal\n  and arbitrary file reads (bsc#1271121).\n- CVE-2026-59925: quadratic-time parsing on long runs of some emphasis pairs in `inline_parser` can lead to DoS\n  (bsc#1271125).\n- CVE-2026-59926: improper escaping in `render_admonition()` can lead to atribute injection and XSS (bsc#1271127).\n- CVE-2026-59927: uncontrolled recursion when processing two markdown files that include each other can lead to a DoS\n   (bsc#1271128).\n- CVE-2026-59928: quadratic-time parsing on long lists of repeated reference-link definitions in `block_parser` can\n  lead to DoS (bsc#1271131).\n- CVE-2026-59929: HARMFUL_PROTOCOLS list misses legacy and chained schemes and allow arbitrary script execution in\n  user agents (bsc#1271132).\n- CVE-2026-59930: the `toc` plugin and `TableOfContents` directive generate heading IDs with predictable values and\n  allow for collisions with attacker-controlled `id=\"toc_N\"` content (bsc#1271082).\n","status":"published","published":"2026-07-14T10:37:38Z","modified":"2026-07-17T18:24:05.645518218Z","updated_at":"2026-11-02T15:54:03.080707Z"}]}}