Description
Starting in Python 3.12.0, the asyncio._SelectorSocketTransport.writelines() method would not "pause" writing and signal to the Protocol to drain the buffer to the wire once the write buffer reached the "high-water mark". Because of this, Protocols would not periodically drain the write buffer potentially leading to memory exhaustion. This vulnerability likely impacts a small number of users, you must be using Python 3.12.0 or later, on macOS or Linux, using the asyncio module with protocols, and using .writelines() method which had new zero-copy-on-write behavior in Python 3.12.0 and later. If not all of these factors are true then your usage of Python is unaffected.
CVSS breakdown
CVSS 4.0
Attack Vector
Network
Attack Complexity
Low
Attack Requirements
None
Privileges Required
None
User Interaction
None
Confidentiality (Vulnerable System)
None
Integrity (Vulnerable System)
None
Availability (Vulnerable System)
High
Confidentiality (Subsequent System)
None
Integrity (Subsequent System)
None
Availability (Subsequent System)
None
CVSS 3.1
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High
Affected products
- Python Software Foundation / CPython3.12.0 – 3.12.9
- Python Software Foundation / CPython3.13.0 – 3.13.2
- Python Software Foundation / CPython3.14.0a1 – 3.14.0a3
References
- MISChttps://github.com/python/cpython/issues/127655
- PATCHhttps://github.com/python/cpython/pull/127656
- MISChttps://mail.python.org/archives/list/security-announce@python.org/thread/H4O3UBAOAQQXGT4RE3E4XQYR5XLROORB/
- PATCHhttps://github.com/python/cpython/commit/71e8429ac8e2adc10084ab5ec29a62f4b6671a82
- PATCHhttps://github.com/python/cpython/commit/9aa0deb2eef2655a1029ba228527b152353135b5
- PATCHhttps://github.com/python/cpython/commit/e991ac8f2037d78140e417cc9a9486223eb3e786