Client memory exhaustion via oversized Content-Length
Published Dec 1, 2025 · Updated Mar 3, 2026
Denial of service in Python Software Foundation CPython allows remote attackers to exhaust client memory through a malicious HTTP response. HTTPResponse.read() without an amount trusts the server's Content-Length and allocates that full size before receiving the response body. Exploitation requires a CPython application to read an attacker-controlled server response without a byte limit, causing swapping, out-of-memory termination, or another service interruption.
Summary
What happened
Denial of service in Python Software Foundation CPython allows remote attackers to exhaust client memory through a malicious HTTP response. HTTPResponse.read() without an amount trusts the server's Content-Length and allocates that full size before receiving the response body. Exploitation requires a CPython application to read an attacker-controlled server response without a byte limit, causing swapping, out-of-memory termination, or another service interruption.
The record
- CVE
- CVE-2025-13836
- Published
- Dec 1, 2025
- Updated
- Mar 3, 2026
- Vendor
- Python Software Foundation
- Product
- CPython
- Classifications
- CWE-400, T1499.004
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Dec 1, 2025CVE publishedPublication date reported by the CVE source.
- Mar 3, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
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- Affected versionversion=0 <3.10.20
- Affected versionversion=3.11.0 <3.11.15
- Affected versionversion=3.12.0 <3.12.13
- Affected versionversion=3.13.0 <3.13.11
- Affected versionversion=3.14.0 <3.14.1
- Affected versionversion=3.15.0a1 <3.15.0a3
What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
What attackers are doing with it
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Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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