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CVE Record

CVE-2026-3298: Out-of-bounds write in Windows asyncio.ProacterEventLoop.sock_recvfrom_into() when using nbytes

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.

HighCVSS 8.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A Windows-only CPython networking flaw can write beyond an application's memory buffer when affected asyncio code receives more data than the buffer allows. A reachable service using this specific API pattern could crash or suffer memory corruption. Linux and other non-Windows systems are not affected.

Executive priority

Treat as a high-priority, targeted remediation rather than an enterprise-wide emergency. Quickly identify Windows Python network services using the affected asyncio method, prioritize externally reachable instances, and apply vendor-fixed builds. The absence of documented active exploitation lowers immediate crisis urgency but does not reduce the memory-corruption risk.

Technical view

asyncio.ProacterEventLoop.sock_recvfrom_into() lacked a boundary check when the nbytes parameter exceeded the supplied buffer capacity. An oversized received datagram could therefore cause a CWE-787 out-of-bounds write. CVSS 4.0 rates it 8.8: network-reachable, low complexity, no privileges or user interaction, with high availability impact and limited confidentiality and integrity impact.

Likely exposure

Exposure requires Windows CPython software that calls sock_recvfrom_into() with nbytes and can receive attacker-controlled network data larger than the destination buffer. The supplied record lists CPython 3.12.0, 3.13.0, 3.14.0a1, and 3.15.0a1, but does not establish complete affected version ranges. Inventory actual runtime versions and application call paths.

Exploitation context

The CVSS vector indicates potential remote, low-complexity exploitation without privileges or user interaction. However, the bundle provides no evidence of exploitation in the wild, and the CVE is not listed as KEV. Practical reachability depends on an application using the vulnerable Windows asyncio API with unsafe nbytes handling.

Researcher notes

The vulnerable condition is narrower than merely running Python on Windows: the application must use ProactorEventLoop.sock_recvfrom_into() with nbytes and an undersized buffer. The source bundle links multiple CPython patches, but does not specify complete vulnerable or fixed release ranges. Validate fixes against the vendor advisory and referenced commits without extrapolating unsupported versions.

Mitigation direction

  • Follow the Python security advisory and install an official release containing the referenced boundary-check patches.
  • Prioritize internet-facing Windows services using asyncio datagram receive operations.
  • Until updated, avoid passing nbytes values greater than the destination buffer capacity.
  • Restrict untrusted network access to affected services where operationally feasible.

Validation and detection

  • Confirm affected applications run CPython on Windows; exclude non-Windows deployments.
  • Search application and dependency code for sock_recvfrom_into() calls using nbytes.
  • Verify nbytes never exceeds the writable destination buffer size.
  • Confirm the installed CPython build includes the vendor's referenced fix.
  • Re-test affected network receive paths after updating.
Prepared
Confidence
high
Sources
10

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

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cwe · low confidence lookup

CWE-787: Exact CWE lookup

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cve · low confidence lookup

CVE-2026-3298 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
8.8 (4.0)
Known Exploited
No
Published

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

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
3Timeline events
1ADP providers
9Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: partial

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
8.8CVSS 4.0HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:H/SC:N/SI:N/SA:N——PSF

Vulnerability scoring details

Base CVSS 4.0 score

8.8High
CVSS 4.0 vector shape for CVE-2026-3298Attack VectorAttack ComplexityAttack RequirementsPrivileges RequiredUser InteractionVS ConfidentialityVS IntegrityVS AvailabilitySS ConfidentialitySS IntegritySS Availability

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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Attack Requirements
NonePresent
Privileges Required
NoneLowHigh
User Interaction
NonePassiveActive
VS Confidentiality
HighLowNone
VS Integrity
HighLowNone
VS Availability
HighLowNone
SS Confidentiality
HighLowNone
SS Integrity
HighLowNone
SS Availability
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
other:ssvc

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
Python Software FoundationCPython0, 3.12.0, 3.13.0, 3.14.0a1, 3.15.0a1unaffected
Weakness

CWE details

CWE-787

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-787 · source CWE mapping

Out-of-bounds Write

Out-of-bounds Write represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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