GHSA-R6H4-MM7H-8PMQ
Vulnerability from github – Published: 2025-12-16 20:46 – Updated: 2025-12-16 20:46Impact
This issue describes a ReDOS bug found within the figure caption extension (pymdownx.blocks.caption ).
In systems that take unchecked user content, this could cause long hangs when processing the data if a malicious payload was crafted.
Patches
This issue is patched in Release 10.16.1.
Workarounds
Some possible workarounds
If users are concerned about this vulnerability and process unknown user content without timeouts or other safeguards in place to prevent really large, malicious content being aimed at systems, the use of pymdownx.blocks.caption could be avoided until the library is updated to 10.16.1+.
References
The original issue https://github.com/facelessuser/pymdown-extensions/issues/2716.
Description
The original issue came through PyMdown Extensions' normal issue tracker instead of the typical security flow: https://github.com/facelessuser/pymdown-extensions/issues/2716. Because this came through the normal issue flow, it was handled as a normal issue. In the future, PyMdown Extensions will ensure such issues, even if prematurely made public through the normal issue flow, are redirected through the typical security process.
The regular expression pattern in question is as follows:
RE_FIG_NUM = re.compile(r'^(\^)?([1-9][0-9]*(?:.[1-9][0-9]*)*)(?= |$)')
The POC was provided by @ShangzhiXu
import re
import time
regex_pattern = re.compile(r'^(\^)?([1-9][0-9]*(?:.[1-9][0-9]*)*)(?= |$)')
for i in range(50, 500, 50):
long_string = '1' * i + 'a'
start_time = time.time()
match = re.match(regex_pattern, long_string)
end_time = time.time()
print(f"long_string execution time: {end_time - start_time:.6f} s")
The issue with the above pattern is that . was used, which accepts any character when we meant to use \.. The fix was to update the pattern to:
RE_FIG_NUM = re.compile(r'^(\^)?([1-9][0-9]*(?:\.[1-9][0-9]*)*)(?= |$)')
Relevant PR with fix: https://github.com/facelessuser/pymdown-extensions/pull/2717
Version(s) & System Info
- Operating System: Any
- Python Version: Any
{
"affected": [
{
"package": {
"ecosystem": "PyPI",
"name": "pymdown-extensions"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "10.16.1"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2025-68142"
],
"database_specific": {
"cwe_ids": [
"CWE-1333"
],
"github_reviewed": true,
"github_reviewed_at": "2025-12-16T20:46:05Z",
"nvd_published_at": "2025-12-16T18:16:16Z",
"severity": "LOW"
},
"details": "### Impact\n\nThis issue describes a ReDOS bug found within the figure caption extension (`pymdownx.blocks.caption` ).\n\nIn systems that take unchecked user content, this could cause long hangs when processing the data if a malicious payload was crafted.\n\n### Patches\n\nThis issue is patched in Release [10.16.1](https://pypi.org/project/pymdown-extensions/10.16.1/).\n\n### Workarounds\n\nSome possible workarounds\n\nIf users are concerned about this vulnerability and process unknown user content without timeouts or other safeguards in place to prevent really large, malicious content being aimed at systems, the use of `pymdownx.blocks.caption` could be avoided until the library is updated to 10.16.1+.\n\n### References\n\nThe original issue https://github.com/facelessuser/pymdown-extensions/issues/2716.\n\n### Description\n\nThe original issue came through PyMdown Extensions\u0027 normal issue tracker instead of the typical security flow: https://github.com/facelessuser/pymdown-extensions/issues/2716. Because this came through the normal issue flow, it was handled as a normal issue. In the future, PyMdown Extensions will ensure such issues, even if prematurely made public through the normal issue flow, are redirected through the typical security process.\n\nThe regular expression pattern in question is as follows:\n\n```py\nRE_FIG_NUM = re.compile(r\u0027^(\\^)?([1-9][0-9]*(?:.[1-9][0-9]*)*)(?= |$)\u0027)\n```\n\nThe POC was provided by @ShangzhiXu\n\n```py\nimport re\nimport time\n\nregex_pattern = re.compile(r\u0027^(\\^)?([1-9][0-9]*(?:.[1-9][0-9]*)*)(?= |$)\u0027)\n\nfor i in range(50, 500, 50):\n long_string = \u00271\u0027 * i + \u0027a\u0027\n start_time = time.time()\n match = re.match(regex_pattern, long_string)\n end_time = time.time()\n print(f\"long_string execution time: {end_time - start_time:.6f} s\")\n```\n\nThe issue with the above pattern is that `.` was used, which accepts any character when we meant to use `\\.`. The fix was to update the pattern to:\n\n```py\nRE_FIG_NUM = re.compile(r\u0027^(\\^)?([1-9][0-9]*(?:\\.[1-9][0-9]*)*)(?= |$)\u0027)\n```\n\nRelevant PR with fix: https://github.com/facelessuser/pymdown-extensions/pull/2717\n\n### Version(s) \u0026 System Info\n\n- Operating System: Any\n- Python Version: Any",
"id": "GHSA-r6h4-mm7h-8pmq",
"modified": "2025-12-16T20:46:05Z",
"published": "2025-12-16T20:46:05Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/facelessuser/pymdown-extensions/security/advisories/GHSA-r6h4-mm7h-8pmq"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2025-68142"
},
{
"type": "WEB",
"url": "https://github.com/facelessuser/pymdown-extensions/commit/b50d15a56850ed1408a284bba81cc019c6bd72e8"
},
{
"type": "PACKAGE",
"url": "https://github.com/facelessuser/pymdown-extensions"
},
{
"type": "WEB",
"url": "https://pypi.org/project/pymdown-extensions/10.16.1"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:U",
"type": "CVSS_V4"
}
],
"summary": "PyMdown Extensions has a ReDOS bug in its Figure Capture extension"
}
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.