CVE-2026-81727
Description
A flaw was found in NLTK. This vulnerability, a filesystem containment bypass, allows a local attacker with write access to a shared downloader directory to create special links (hardlinks) that point to files outside the intended installation area. When a package is extracted, these hardlinks can cause files outside the NLTK installation to be overwritten, leading to unauthorized modification or corruption of data.
Statement
The NLTK library is vulnerable to a local file overwrite due to a filesystem containment bypass. An attacker with write access to a shared NLTK downloader directory can exploit this by creating hardlinks, leading to the overwriting of arbitrary files outside the intended installation path during package extraction. This could result in data integrity and availability impacts.
Mitigation
To mitigate this issue, ensure that NLTK downloader directories are not shared among untrusted users or are configured with restrictive permissions to prevent unauthorized write access. If a shared downloader directory is essential, implement strict access controls to limit write permissions to only trusted accounts. This reduces the attack surface by preventing malicious local users from creating hardlinks to arbitrary files.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.1 | N/A | 7.1 |
| Attack Vector | Local | N/A | Local |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | Low | N/A | Low |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | None | N/A | None |
| Integrity Impact | High | N/A | High |
| Availability Impact | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H
cve.org: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H
Understanding the Weakness (CWE)
Confidentiality,Integrity,Access Control
Technical Impact: Read Files or Directories; Modify Files or Directories; Bypass Protection Mechanism
An attacker may be able to traverse the file system to unintended locations and read or overwrite the contents of unexpected files. If the files are used for a security mechanism then an attacker may be able to bypass the mechanism.
Other
Technical Impact: Execute Unauthorized Code or Commands
Windows simple shortcuts, sometimes referred to as soft links, can be exploited remotely since a ".LNK" file can be uploaded like a normal file. This can enable remote execution.
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