CVE-2026-78682
Description
A flaw was found in NLTK. When an HTTP proxy is configured, a server-side request forgery (SSRF) vulnerability exists in the nltk.pathsec.urlopen function. An attacker can exploit this by providing a seemingly valid public URL, which the proxy then forwards to an internal service without proper re-validation. This could lead to the disclosure of internal network resources, the loading of malicious downloader indexes, and the installation of attacker-controlled package content.
Statement
This is a server-side request forgery (SSRF) vulnerability in NLTK when an HTTP proxy is configured. The flaw allows an attacker to bypass local hostname validation, enabling the proxy to forward requests to internal loopback services. This can lead to the disclosure of internal HTTP resources or the installation of attacker-controlled package content in Red Hat products utilizing NLTK with an HTTP proxy.
Mitigation
To mitigate this issue, avoid configuring an HTTP proxy for NLTK if it is not strictly necessary. If an HTTP proxy must be used, implement strict network egress filtering to prevent NLTK from initiating connections to internal or loopback network addresses. This measure restricts the potential for an attacker to exploit the SSRF to access internal resources.
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).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.5 | N/A | 7.5 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | High | N/A | High |
| Integrity Impact | None | N/A | None |
| Availability Impact | None | N/A | None |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Understanding the Weakness (CWE)
Confidentiality
Technical Impact: Read Application Data
Integrity
Technical Impact: Execute Unauthorized Code or Commands
Access Control
Technical Impact: Bypass Protection Mechanism
By providing URLs to unexpected hosts or ports, attackers can make it appear that the server is sending the request, possibly bypassing access controls such as firewalls that prevent the attackers from accessing the URLs directly. The server can be used as a proxy to conduct port scanning of hosts in internal networks, use other URLs such as that can access documents on the system (using file://), or use other protocols such as gopher:// or tftp://, which may provide greater control over the contents of requests.
Frequently Asked Questions
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