CVE-2026-65915VulnerabilityPublished 2 Sep 2026Updated 29 Oct 2026

safety · NLTK: FileSystemPathPointer.open() sandbox check is dead code — arbitrary file read via file:// protocol

Affects safetySource GCVE Database

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Not known to be exploited · CVSS 6.5 Medium : upgrade to 3.8.1_1 when convenient.

Data as of 30 Oct 2026, 07:30 UTC

CVSS 3.1 base score

6.5Medium

How severe the flaw is on the 0–10 CVSS scale.

Patch: Available – fixed in 3.8.1_1

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

Attack Vector: Network
Attack Complexity: Low
Privileges Required: Low
User Interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: None
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 2 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade safety to 3.8.1_1.

Affected software

Product	Affected	Fixed in
Homebrewsafety`pkg:brew/safety`Other threats	Affected >=3.3.1 <3.8.1_1	Fixed in 3.8.1_1

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

Description

### Summary There's a logic bug in `FileSystemPathPointer.open()` inside `nltk/data.py` that makes the sandbox check permanently inert. The guard condition is always `False` — meaning any file the process can read is accessible by passing a `file://` URL to `nltk.data.load()`. --- ### Details In `nltk/data.py`, `FileSystemPathPointer.open()` was patched at some point with a comment saying "SECURITY PATCH ENFORCING SANDBOX", but the check doesn't work: ```python def open(self, encoding=None): path = os.path.normpath(self._path) # Block raw absolute reads such as "/" "C:\\Windows" etc. if os.path.isabs(path) and path != os.path.normpath(self._path): raise ValueError(f"Direct absolute file access blocked: {path}") stream = open(self._path, "rb") ``` `path` is set to `os.path.normpath(self._path)` on line 1, then compared against `os.path.normpath(self._path)` again in the condition. They are always equal. The `ValueError` never fires. On top of that, `__init__` already calls `os.path.abspath()` before storing `self._path`, so it's normalized before `open()` is even called. Running `normpath` on it again changes nothing. The `stream = open(self._path, "rb")` line is always reached regardless of what path was passed in. --- ### PoC Tested on Python 3.11, NLTK 3.9.1, Ubuntu 22.04. ```python import nltk from nltk.data import FileSystemPathPointer # direct construction ptr = FileSystemPathPointer("/etc/passwd") with ptr.open() as f: print(f.read(300)) # via load() using file:// URL data = nltk.data.load("file:///etc/passwd", format="raw") print(data[:300]) ``` Both print file contents. No exception is raised. --- ### Impact Any app that lets users influence the string passed to `nltk.data.load()` or `nltk.data.find()` is exposed — web APIs, notebook servers, multi-tenant pipelines. An attacker can read any file the process user has access to: `/etc/passwd`, `.env` files, private keys, `~/.aws/credentials`, etc. ## Suggested Fix **File:** `nltk/data.py` — `FileSystemPathPointer.open()` (lines 378–390) ### What's wrong Line 387 compares `normpath(self._path)` against itself — always equal, so the `ValueError` never fires. The check is dead code. `__init__` already calls `abspath()` on construction, so re-running `normpath` inside `open()` changes nothing either. --- ### Fix Validate against the actual list of permitted data directories instead: ```python def open(self, encoding=None): import nltk.data as _d allowed = [os.path.abspath(p) for p in _d.path if p] if allowed and not any( os.path.commonpath([self._path, r]) == r for r in allowed ): raise ValueError( f"Access outside nltk_data blocked: {self._path!r}" ) stream = open(self._path, "rb") if encoding is not None: stream = SeekableUnicodeStreamReader(stream, encoding) return stream ``` --- ### Why `commonpath` not `startswith` `startswith` is bypassable by a path that shares a prefix: ``` /tmp/nltk_data_evil".startswith("/tmp/nltk_data") → True ✗ commonpath(["/tmp/nltk_data_evil", "/tmp/nltk_data"]) → "/tmp" ✓ ``` --- ### Diff ```diff - path = os.path.normpath(self._path) - if os.path.isabs(path) and path != os.path.normpath(self._path): - raise ValueError(f"Direct absolute file access blocked: {path}") - + import nltk.data as _d + allowed = [os.path.abspath(p) for p in _d.path if p] + if allowed and not any( + os.path.commonpath([self._path, r]) == r for r in allowed + ): + raise ValueError(f"Access outside nltk_data blocked: {self._path!r}") stream = open(self._path, "rb") ```

References

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