CyberSecBulletin
CVE-2025-13836NVD status: Analyzed

CPython: Uncontrolled Resource Consumption

Published Updated By the CyberSecBulletin desk

CVE-2025-13836 is a high-severity uncontrolled resource consumption vulnerability in CPython from Python Software Foundation, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions 3.10.20, 3.11.15, 3.12.13 as the first without the flaw, so updating CPython to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 1.75% chance of exploitation within 30 days, higher than 78% of scored CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update CPython to 3.10.20 or 3.11.15 or 3.12.13 or 3.13.11, whichever matches your release line, or a later version.
  2. Update Python to 3.10.20 or 3.11.15 or 3.12.13 or 3.13.11, whichever matches your release line, or a later version.
  3. Read the advisory on mail.python.org for workarounds and exact fixed builds.
  4. Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.

Affected products and versions

VendorProductAffected versionsFixed in
Python Software FoundationCPythonbefore 3.10.20; 3.11.0 up to, but not including, 3.11.15; 3.12.0 up to, but not including, 3.12.13; 3.13.0 up to, but not including, 3.13.11; 3.14.0 up to, but not including, 3.14.1; 3.15.0a1 up to, but not including, 3.15.0a33.10.20, 3.11.15, 3.12.13, 3.13.11, 3.14.1, 3.15.0a3
PythonPythonbefore 3.10.20; 3.11.0 up to, but not including, 3.11.15; 3.12.0 up to, but not including, 3.12.13; 3.13.0 up to, but not including, 3.13.11; 3.14.0; 3.15.03.10.20, 3.11.15, 3.12.13, 3.13.11

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
NetworkCan be exploited remotely over a network, including the internet.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
NoneNo account or login is needed.
User interaction
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
NoneNo data is disclosed.
Integrity
NoneNothing can be modified.
Availability
HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. Scored by NVD.

Scoring systemScoreSeverityScored by
CVSS 4.06.3MediumCNA (python.org)
CVSS 3.17.5HighNVD

Official description

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.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Uncontrolled Resource Consumption

The product does not properly control the allocation and maintenance of a limited resource.

How developers prevent this class of flaw

  • Ensure that protocols have specific limits of scale placed on them.
  • Ensure that all failures in resource allocation place the system into a safe posture.

More Uncontrolled Resource Consumption vulnerabilities (CWE-400)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: partial).
  3. Record last changed materially (score, affected products, status or references).

References

Other vulnerabilities in CPython

All CPython vulnerabilities

Recent Uncontrolled Resource Consumption vulnerabilities

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