Upstream information
Description
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.SUSE information
Overall state of this security issue: Pending
This issue is currently rated as having important severity.
| CVSS detail | CNA (GitHub) | SUSE |
|---|---|---|
| Base Score | 7.5 | 7.5 |
| Vector | CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
| Attack Vector | Network | Network |
| Attack Complexity | Low | Low |
| Privileges Required | None | None |
| User Interaction | None | None |
| Scope | Unchanged | Unchanged |
| Confidentiality Impact | None | None |
| Integrity Impact | None | None |
| Availability Impact | High | High |
| CVSSv3 Version | 3 | 3.1 |
| CVSS detail | SUSE |
|---|---|
| Base Score | 8.7 |
| Vector | CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N |
| Attack Vector | Network |
| Attack Complexity | Low |
| Attack Requirements | None |
| Privileges Required | None |
| User Interaction | None |
| Vulnerable System Confidentiality Impact | None |
| Vulnerable System Integrity Impact | None |
| Vulnerable System Availability Impact | High |
| Subsequent System Confidentiality Impact | None |
| Subsequent System Integrity Impact | None |
| Subsequent System Availability Impact | None |
| CVSSv4 Version | 4.0 |
Status of this issue by product and package
Please note that this evaluation state might be work in progress, incomplete or outdated. Also information for service packs in the LTSS phase is only included for issues meeting the LTSS criteria. If in doubt, feel free to contact us for clarification. The updates are grouped by state of their lifecycle. SUSE product lifecycles are documented on the lifecycle page.
| Product(s) | Source package | State |
|---|---|---|
| Products under general support and receiving all security fixes. | ||
| SUSE Linux Enterprise Server 16.0 | python-cbor2 | In progress |
| SUSE Linux Enterprise Server 16.1 | python-cbor2 | Affected |
| SUSE Linux Enterprise Server for SAP applications 16.0 | python-cbor2 | In progress |
| SUSE Linux Enterprise Server for SAP applications 16.1 | python-cbor2 | Affected |
SUSE Timeline for this CVE
CVE page created: Mon Mar 23 22:00:13 2026CVE page last modified: Tue Mar 24 19:55:01 2026