Unbounded memory buffering in SelectorSocketTransport.writelines()
Summary
| CVE | CVE-2024-12254 |
|---|---|
| State | PUBLISHED |
| Assigner | PSF |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2024-12-06 16:15:20 UTC |
| Updated | 2026-07-31 15:16:26 UTC |
| 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. |
Risk And Classification
Primary CVSS: v4.0 8.7 HIGH from [email protected]
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
EPSS: 0.018800000 probability, percentile 0.773930000 (date 2026-08-03)
Problem Types: CWE-400 | CWE-770 | CWE-400 CWE-400 Uncontrolled Resource Consumption | CWE-770 CWE-770 Allocation of Resources Without Limits or Throttling
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 4.0 | [email protected] | Secondary | 8.7 | HIGH | CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/C... |
| 4.0 | CNA | CVSS | 8.7 | HIGH | CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N |
| 3.1 | ADP | DECLARED | 7.5 | HIGH | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
| 3.1 | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | Secondary | 7.5 | HIGH | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
CVSS v4.0 Breakdown
Attack Vector
NetworkAttack Complexity
LowAttack Requirements
NonePrivileges Required
NoneUser Interaction
NoneConfidentiality
NoneIntegrity
NoneAvailability
HighSub Conf.
NoneSub Integrity
NoneSub Availability
NoneCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
CVSS v3.1 Breakdown
Attack Vector
NetworkAttack Complexity
LowPrivileges Required
NoneUser Interaction
NoneScope
UnchangedConfidentiality
NoneIntegrity
NoneAvailability
HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Python Software Foundation | CPython | affected 3.12.9 python | MacOS, Linux |
| CNA | Python Software Foundation | CPython | affected 3.13.0 3.13.2 python | MacOS, Linux |
| CNA | Python Software Foundation | CPython | affected 3.14.0a1 3.14.0a3 python | MacOS, Linux |
| ADP | Python Software Foundation | Cpython | affected 3.12.0 3.14.0a1 python | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| www.openwall.com/lists/oss-security/2024/12/06/1 | af854a3a-2127-422b-91ae-364da2661108 | www.openwall.com | |
| github.com/python/cpython/pull/127656 | [email protected] | github.com | |
| github.com/python/cpython/commit/9aa0deb2eef2655a1029ba228527b152353135b5 | [email protected] | github.com | |
| mail.python.org/archives/list/[email protected]/thread/H4O3UBAOAQQ... | [email protected] | mail.python.org | |
| github.com/python/cpython/commit/71e8429ac8e2adc10084ab5ec29a62f4b6671a82 | [email protected] | github.com | |
| security.netapp.com/advisory/ntap-20250404-0010 | af854a3a-2127-422b-91ae-364da2661108 | security.netapp.com | |
| github.com/python/cpython/issues/127655 | [email protected] | github.com | |
| github.com/python/cpython/commit/e991ac8f2037d78140e417cc9a9486223eb3e786 | [email protected] | github.com | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
Vendor Comments And Credit
Discovery Credit
CNA: J. Nick Koston (en)
CNA: Seth Larson (en)
There are currently no legacy QID mappings associated with this CVE.