What’s Vulnerable › Vulnerabilities

CVE-2025-13836: Excessive read buffering DoS in http.client

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-12-01 · updated 2026-09-03
• Weakness: CWE-400

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.

Affected products

• Python: before 3.10.20; from 3.11.0 before 3.11.15; from 3.12.0 before 3.12.13; from 3.13.0 before 3.13.11; 3.14.0, 3.15.0-alpha1, 3.15.0-alpha2 — fixed in 3.10.20, 3.11.15, 3.12.13, 3.13.11

How to fix

Upgrade to a fixed version: Python 3.10.20, 3.11.15, 3.12.13, 3.13.11. Check the vendor advisory for mitigations.

References

• https://github.com/python/cpython/commit/14b1fdb0a94b96f86fc7b86671ea9582b8676628
• https://github.com/python/cpython/commit/289f29b0fe38baf2d7cb5854f4bb573cc34a6a15
• https://github.com/python/cpython/commit/4ce27904b597c77d74dd93f2c912676021a99155
• https://github.com/python/cpython/commit/5a4c4a033a4a54481be6870aa1896fad732555b5
• https://github.com/python/cpython/commit/5dc101675fd22918facbbe0fecdc821502beaaf0
• https://github.com/python/cpython/commit/afc40bdd3dd71f343fd9016f6d8eebbacbd6587c
• https://github.com/python/cpython/issues/119451
• https://github.com/python/cpython/pull/119454
• https://mail.python.org/archives/list/security-announce@python.org/thread/OQ6G7MKRQIS3OAREC3HNG3D2DPOU34XO/

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