CVE-2026-3298: Out-of-bounds write in Windows asyncio.ProacterEventLoop.sock_recvfrom_into() when using nbytes
Noroxi assessment
Priority: Monitor (action score 35/100)
- The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
- Probability of exploitation in the next 30 days: 0.39% (FIRST EPSS).
- Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
- Fixed version: Python Software Foundation CPython 3.11.16, 3.12.14, 3.13.14.
Low priority for now. Upgrade to Python Software Foundation CPython 3.11.16, 3.12.14, 3.13.14 or later.
Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it
Primary sources: NVD · CVE.org · FIRST EPSS
The method "sock_recvfrom_into()" of "asyncio.ProacterEventLoop" (Windows only) was missing a boundary check for the data buffer when using nbytes parameter. This allowed for an out-of-bounds buffer write if data was larger than the buffer size. Non-Windows platforms are not affected.
- Published
- Apr 21, 2026
- Updated
- Oct 26, 2026
- EPSS
- 0.3% · 33th percentile
- CWE
- CWE-787
Report tools
Action score
35
Monitor
Low priority for now.
- CVSS
- 35 / 40 · 8.8 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 0 / 30 · 0.3%
CISA SSVC decision
- Exploitation
- none
- Automatable
- no
- Technical impact
- partial
Vulnrichment: CISA's decision-tree inputs.
CNA vs NVD score
- NVD
- —
- CNA · PSF
- 8.8
- NVD has not scored this yet; the score shown is the CNA’s.
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:H/SC:N/SI:N/SA:N
The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.
Get told when this record changes
- Not in KEV: no record of exploitation in the wild
- No public exploit code on record
- A fix has been released
If any of these changes, we'll tell you in the daily email digest.
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Noroxi analysis
What does it mean in your environment?
The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.
We use this product, ask for helpAffected systems
Is your version affected?
Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.
—
Versions reported by the vendor
Affected version ranges reported by the assigning authority (PSF). Independent of NVD's CPE analysis and usually ahead of it.
Python Software Foundation CPython
- before 3.11.16affected · python
- 3.12.0 and later · before 3.12.14affected · python
- 3.13.0 and later · before 3.13.14affected · python
- 3.14.0a1 and later · before 3.14.5rc1affected · python
- 3.15.0a1 and later · before 3.15.0b1affected · python
Same product
python software foundation: all recordsOther highest-scoring records for the same primary product.
- CVE-2026-115557Distrust compromised intermediate certificates in ssl module37Monitor
- CVE-2025-4517Arbitrary writes via tarfile realpath overflow37Monitor
- CVE-2026-19445Use-after-free of a server-side SSLContext when sni_callback switches contexts36Monitor
Published before and after this one in the same product
- ← EarlierCVE-2026-4786Apr 13, 2026 · Incomplete mitigation of CVE-2026-4519, %action expansion for command injection to webbrowser.open()28Monitor
- ← EarlierCVE-2026-5713Apr 14, 2026 · Out-of-bounds read/write during remote profiling and asyncio process introspection when connecting to malicious target21Monitor
- Later →CVE-2026-8328May 13, 2026 · FTP PASV SSRF, ftpcp() does not use actual peer address, trusts server-supplied PASV host address23Monitor
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
| Product / package | Fixed version | Source |
|---|---|---|
| Python Software Foundation CPython | 3.11.16 | Vendor (CNA) |
| Python Software Foundation CPython | 3.12.14 | Vendor (CNA) |
| Python Software Foundation CPython | 3.13.14 | Vendor (CNA) |
| Python Software Foundation CPython | 3.14.5rc1 | Vendor (CNA) |
| Python Software Foundation CPython | 3.15.0b1 | Vendor (CNA) |
Exploit status
No known public exploit
No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
No dated events beyond publication.
No history yet (it accumulates with the daily EPSS job).
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
- Seth Larson (https://github.com/sethmlarson)coordinator
- GGAutomaton (https://github.com/GGAutomaton)reporter
- Victor Stinner (https://github.com/vstinner)remediation reviewer
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
No nightly-computed relations.
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
—
Bug bounty scope
No known public program.
Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).
Technical details
Attack conditions
- Anyone who can reach it over the internet can trigger it.
- No account or password is required.
- No user action is required.
- No special conditions are required; it is repeatable.
If successful
- Confidentiality
- Integrity
- Availability
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- X
Weakness class (CWE)
CWE-787 · Out-of-bounds WriteCVSS vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/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
nvd-secondary
Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
MITRE has no CAPEC/ATT&CK mapping for this CWE.
Change log
- Fix✗ → ✓
For records you follow, these changes also arrive as notifications. →
References
Show all references (7 more)Show less
- github.com/python/cpython/commit/27522b7d6e6588f03e61099dd858cd5a9314e2f2
- github.com/python/cpython/commit/6c8b85b3f1d83d5697ec19880960e1eacee56688
- github.com/python/cpython/commit/95633d2aad4721e25e4dfd9f43dfb6e1edcbd741
- github.com/python/cpython/commit/f5ca38739241fe7a40a4b116d5a8a1364dd6fea7
- github.com/python/cpython/issues/148808
- github.com/python/cpython/pull/148809
- mail.python.org/archives/list/security-announce@python.org/thread/KWTPIQBOOOUNQP7UFSLBI437NJDFLA3F/
Vendor advisories and official records. Exploit/PoC links are deliberately left out.