CVE-2025-13836

When reading an HTTP response from a server, if no read amount is specified, the default behavior will be to use Content-Length. This allows a malicious server to cause the client to read large amounts of data into memory, potentially causing OOM or other DoS.

What this means for your business

It affects Python. It matters if your company, or a supplier that handles your data, runs it.
An attacker can use it remotely, over a network, without a login, and without anyone at your company clicking anything.
FIRST's prediction model gives it a 2% chance of attack attempts being seen in the next 30 days, ranking above 74% of all known flaws.

What to do

1Check whether your company or your suppliers run Python, and which version. The affected versions are listed further down this page.
2If you do, apply the vendor's fix. A patch or vendor advisory has been published.

Not sure if your company is exposed?

Fastnexa’s certified penetration testers can check whether attackers could use this flaw, or others like it, against your websites, apps and network. The full test is free for our first 10 founding clients until 31 December 2026.

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Scoring

CVSS: 7.5 (v3.1)
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS v4: 6.3
Weakness: CWE-400
Assigned by: cna@python.org

Dates

Published: 2025-12-01
Last modified: 2026-09-03
Sources: NVD

Affected products

Python Python- 3.10.20, 3.11.0 - 3.11.15, 3.12.0 - 3.12.13, 3.13.0 - 3.13.11, 3.14.0, 3.15.0

As listed in the NVD configuration data. Not a statement about your estate.