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.

The remote openSUSE 16 host has a package installed that is affected by multiple vulnerabilities as referenced in the openSUSE-SU-2026:20468-1 advisory.

    - CVE-2025-68131: CBORDecoder reuse across trust boundaries can lead to leak of shareable values from     previous decode       calls via attacker-controlled messages (bsc#1255783).
    - CVE-2026-26209: uncontrolled recursion via crafted CBOR payloads can cause a denial of service     (bsc#1260367).

Tenable has extracted the preceding description block directly from the SUSE security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

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.

There are packages installed that are affected by a vulnerability referenced in the following CVE:

  - 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)

ID	Name	Product	Family	Severity
305837	openSUSE 16 Security Update : python-cbor2 (openSUSE-SU-2026:20468-1)	Nessus	SuSE Local Security Checks	medium
303649	Linux Distros Unpatched Vulnerability : CVE-2026-26209	Nessus	Misc.	high
439131	SCA: security update for cbor2 (GHSA-3c37-wwvx-h642)	Tenable Cloud Security	SCA Checks	high
439131	SCA: security update for cbor2 (GHSA-3c37-wwvx-h642)	Tenable Self-Hosted Container Security	SCA Checks	high

Detections

Analytics

CVE-2026-26209

high

Tenable Plugins

medium

high

high

high