high CVSS 7.5

CVE-2026-44660·Python vulnerability

UltraJSON is a fast JSON encoder and decoder written in pure C with bindings for Python 3.7+. Prior to 5.12.1, when ujson.dump() writes to a file-like object and the write operation raises an exception, the serialized JSON string object is not decremented, leaking memory. Each failed write operation leaks the full size of the serialized payload. This vulnerability is fixed in 5.12.1.

Severity
high
Software
Python
Fixed in
5.12.1
Published
2026-05-27

Affected versions

Until: 5.12.1

Fixed in: 5.12.1

How to fix this CVE

Upgrade UltraJSON to version 5.12.1 or later to patch a memory leak vulnerability in the ujson.dump() function. When file write operations fail, the serialized JSON string objects were not being properly freed, causing cumulative memory exhaustion with each failed write. Apply this update immediately in environments where ujson handles untrusted or high-volume JSON serialization tasks.

sudo dnf update python3-ujson

Defensia detects this vulnerability

How to check if you are affected

  1. Check installed UltraJSON version: python3 -c "import ujson; print(ujson.__version__)"
  2. Verify if ujson is imported in your application: grep -r "import ujson" /opt /home /var/www --include="*.py"
  3. Monitor system memory usage during JSON serialization operations: watch -n 1 'ps aux | grep -E "python.*ujson" | head -5'
  4. Confirm the patch by re-running the version check after update and verifying output shows 5.12.1 or later

FAQ

What is CVE-2026-44660?

This is a memory leak vulnerability in UltraJSON where failed file write operations during ujson.dump() calls fail to release the serialized JSON string object, allowing attackers to exhaust memory by triggering repeated write failures.

Is CVE-2026-44660 being actively exploited?

No, this vulnerability is not listed in the CISA KEV catalog and there is no known public exploit available, though the condition can be triggered through application-level error handling.

What versions of Python are affected by CVE-2026-44660?

UltraJSON versions prior to 5.12.1 are affected. The library supports Python 3.7 and later, so any application using ujson < 5.12.1 on these Python versions is vulnerable.

How do I check if my server is vulnerable to CVE-2026-44660?

Run 'python3 -c "import ujson; print(ujson.__version__)"' and compare the output to version 5.12.1; versions below 5.12.1 are vulnerable.

Does Defensia detect CVE-2026-44660?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Python and UltraJSON are present on a monitored server, CVE-2026-44660 will appear in your dashboard with remediation steps.

Related Python CVEs

CVE-2026-28505CVSS 10Tautulli is a Python based monitoring and tracking tool for Plex Media Server. Prior to version 2.17.0, the str_eval() function in notification_handler.py implements a sandboxed eval() for notification text templates. The sandbox attempts to restrict callable names by inspecting code.co_names of the compiled code object. However, co_names only contains names from the outer code object. When a lambda expression is used, it creates a nested code object whose attribute accesses are stored in code.co_consts, NOT in code.co_names. The sandbox never inspects nested code objects. This issue has been patched in version 2.17.0.
CVE-2026-25632CVSS 10EPyT-Flow is a Python package designed for the easy generation of hydraulic and water quality scenario data of water distribution networks. Prior to 0.16.1, EPyT-Flow’s REST API parses attacker-controlled JSON request bodies using a custom deserializer (my_load_from_json) that supports a type field. When type is present, the deserializer dynamically imports an attacker-specified module/class and instantiates it with attacker-supplied arguments. This allows invoking dangerous classes such as subprocess.Popen, which can lead to OS command execution during JSON parsing. This also affects the loading of JSON files. This vulnerability is fixed in 0.16.1.
CVE-2026-34938CVSS 10PraisonAI is a multi-agent teams system. Prior to version 1.5.90, execute_code() in praisonai-agents runs attacker-controlled Python inside a three-layer sandbox that can be fully bypassed by passing a str subclass with an overridden startswith() method to the _safe_getattr wrapper, achieving arbitrary OS command execution on the host. This issue has been patched in version 1.5.90.
CVE-2026-33054CVSS 10Mesop is a Python-based UI framework that allows users to build web applications. Versions 1.2.2 and below contain a Path Traversal vulnerability that allows any user supplying an untrusted state_token through the UI stream payload to arbitrarily target files on the disk under the standard file-based runtime backend. This can result in application denial of service (via crash loops when reading non-msgpack target files as configurations), or arbitrary file manipulation. This vulnerability heavily exposes systems hosted utilizing FileStateSessionBackend. Unauthorized malicious actors could interact with arbitrary payloads overwriting or explicitly removing underlying service resources natively outside the application bounds. This issue has been fixed in version 1.2.3.
CVE-2026-25115CVSS 9.9n8n is an open source workflow automation platform. Prior to version 2.4.8, a vulnerability in the Python Code node allows authenticated users to break out of the Python sandbox environment and execute code outside the intended security boundary. This issue has been patched in version 2.4.8.

References

Track CVEs across your fleet automatically

Defensia scans your Linux servers and tells you exactly which ones are running vulnerable versions — including CVE-2026-44660. Free for 1 server.

Get started free