CVE-2026-26209 | agronholm cbor2 up to 5.8.x cbor2.loads recursion

VDB-352570 · CVE-2026-26209 · GCVE-0-2026-26209 AGRONHOLM CBOR2 UP TO 5.8.X CBOR2.LOADS RECURSION HISTORYDIFFRELATEJSONXMLCTI CVSS Meta Temp Score Current Exploit Price (≈) CTI Interest Score 6.3 $0-$5k 2.50+ Summaryinfo A vulnerability categorized as problematic has been discovered in agronholm cbor2 up to 5.8.x. This impacts the function cbor2.loads. Executing a manipulation can lead to recursion. This vulnerability is registered as CVE-2026-26209. It is possible to launch the attack remotely. No exploit is available. It is advisable to upgrade the affected component. Detailsinfo A vulnerability has been found in agronholm cbor2 up to 5.8.x and classified as problematic. This vulnerability affects the function cbor2.loads. The manipulation with an unknown input leads to a recursion vulnerability. The CWE definition for the vulnerability is CWE-674. The product does not properly control the amount of recursion that takes place, consuming excessive resources, such as allocated memory or the program stack. As an impact it is known to affect availability. CVE summarizes: 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 advisory is available at github.com. This vulnerability was named CVE-2026-26209 since 02/11/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. Technical details are known, but there is no available exploit. This vulnerability is assigned to T1499 by the MITRE ATT&CK project. Upgrading to version 5.9.0 eliminates this vulnerability. Productinfo Vendor agronholm Name cbor2 Version 5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 Website Product: https://github.com/agronholm/cbor2/ CPE 2.3info 🔒 🔒 🔒 CPE 2.2info 🔒 🔒 🔒 CVSSv4info VulDB Vector: 🔒 VulDB Reliability: 🔍 CVSSv3info VulDB Meta Base Score: 6.4 VulDB Meta Temp Score: 6.3 VulDB Base Score: 5.3 VulDB Temp Score: 5.1 VulDB Vector: 🔒 VulDB Reliability: 🔍 CNA Base Score: 7.5 CNA Vector (GitHub_M): 🔒 CVSSv2info Vector Complexity Authentication Confidentiality Integrity Availability Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock VulDB Base Score: 🔒 VulDB Temp Score: 🔒 VulDB Reliability: 🔍 Exploitinginfo Class: Recursion CWE: CWE-674 / CWE-404 CAPEC: 🔒 ATT&CK: 🔒 Physical: No Local: No Remote: Yes Availability: 🔒 Status: Not defined Price Prediction: 🔍 Current Price Estimation: 🔒 0-Day Unlock Unlock Unlock Unlock Today Unlock Unlock Unlock Unlock Threat Intelligenceinfo Interest: 🔍 Active Actors: 🔍 Active APT Groups: 🔍 Countermeasuresinfo Recommended: Upgrade Status: 🔍 0-Day Time: 🔒 Upgrade: cbor2 5.9.0 Timelineinfo 02/11/2026 CVE reserved 03/23/2026 +40 days Advisory disclosed 03/23/2026 +0 days VulDB entry created 03/23/2026 +0 days VulDB entry last update Sourcesinfo Product: github.com Advisory: github.com Status: Confirmed CVE: CVE-2026-26209 (🔒) GCVE (CVE): GCVE-0-2026-26209 GCVE (VulDB): GCVE-100-352570 Entryinfo Created: 03/23/2026 20:11 Changes: 03/23/2026 20:11 (63) Complete: 🔍 Cache ID: 99:1CC:101 Discussion No comments yet. Languages: en. Please log in to comment. ◂ PreviousOverviewNext ▸