Linux Distros Unpatched Vulnerability : CVE-2026-26209

high Nessus Plugin ID 303649

Synopsis

The Linux/Unix host has one or more packages installed with a vulnerability that the vendor indicates will not be patched.

Description

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

- cbor2 provides encoding and decoding for the Concise Binary Object Representation (CBOR) serialization format. Versions prior to 5.9.0 are vulnerable to a Denial of Service (DoS) attack caused by uncontrolled recursion when decoding deeply nested CBOR structures. This vulnerability affects both the pure Python implementation and the C extension `_cbor2`. The C extension relies on Python's internal recursion limits `Py_EnterRecursiveCall` rather than a data-driven depth limit, meaning it still raises `RecursionError` and crashes the worker process when the limit is hit. While the library handles moderate nesting levels, it lacks a hard depth limit. An attacker can supply a crafted CBOR payload containing approximately 100,000 nested arrays `0x81`. When `cbor2.loads()` attempts to parse this, it hits the Python interpreter's maximum recursion depth or exhausts the stack, causing the process to crash with a `RecursionError`. Because the library does not enforce its own limits, it allows an external attacker to exhaust the host application's stack resource. In many web application servers (e.g., Gunicorn, Uvicorn) or task queues (Celery), an unhandled `RecursionError` terminates the worker process immediately. By sending a stream of these small (<100KB) malicious packets, an attacker can repeatedly crash worker processes, resulting in a complete Denial of Service for the application. Version 5.9.0 patches the issue.
(CVE-2026-26209)

Note that Nessus relies on the presence of the package as reported by the vendor.

Solution

There is no known solution at this time.

Plugin Details

Severity: High

ID: 303649

File Name: unpatched_CVE_2026_26209.nasl

Version: 1.2

Type: local

Agent: unix

Family: Misc.

Published: 3/25/2026

Updated: 3/26/2026

Supported Sensors: Agentless Assessment, Frictionless Assessment Agent, Frictionless Assessment AWS, Frictionless Assessment Azure, Nessus Agent, Nessus

Risk Information

VPR

Risk Factor: Medium

Score: 4.4

CVSS v2

Risk Factor: Medium

Base Score: 5

Temporal Score: 4.5

Vector: CVSS2#AV:N/AC:L/Au:N/C:N/I:N/A:P

CVSS Score Source: CVE-2026-26209

CVSS v3

Risk Factor: High

Base Score: 7.5

Temporal Score: 7.1

Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Temporal Vector: CVSS:3.0/E:P/RL:U/RC:C

Vulnerability Information

CPE: cpe:/o:debian:debian_linux:11.0, cpe:/o:canonical:ubuntu_linux:25.10, cpe:/o:canonical:ubuntu_linux:24.04:-:lts, p-cpe:/a:canonical:ubuntu_linux:cbor2, cpe:/o:canonical:ubuntu_linux:22.04:-:lts, cpe:/o:debian:debian_linux:14.0, p-cpe:/a:debian:debian_linux:cbor2, cpe:/o:debian:debian_linux:12.0, cpe:/o:debian:debian_linux:13.0

Required KB Items: Host/cpu, Host/local_checks_enabled, global_settings/vendor_unpatched, Host/OS/identifier

Exploit Available: true

Exploit Ease: Exploits are available

Vulnerability Publication Date: 3/23/2026

Reference Information

CVE: CVE-2026-26209

Detections

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