CVE-2026-43678Public exploitNetwork attack vector

Process crash via WebSocket length Int trap

Published Aug 20, 2026 · Updated Aug 20, 2026

Denial of service in Apple SwiftNIO before 2.101.0 allows remote attackers to crash NIOWebSocket-based servers via a crafted frame. In WebSocketFrameDecoder, the 8-byte extended payload length is converted with Swift's trapping Int(_:) initializer, so a 64-bit length with the high bit set aborts the process before maxFrameSize validation runs. The attack requires only a completed WebSocket handshake and one 11-byte frame from an unauthenticated remote peer, interrupting all active connections until the server restarts.

CVSS severity7.5
High
EPSS probability0.29%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Apple SwiftNIO before 2.101.0 allows remote attackers to crash NIOWebSocket-based servers via a crafted frame. In WebSocketFrameDecoder, the 8-byte extended payload length is converted with Swift's trapping Int(_:) initializer, so a 64-bit length with the high bit set aborts the process before maxFrameSize validation runs. The attack requires only a completed WebSocket handshake and one 11-byte frame from an unauthenticated remote peer, interrupting all active connections until the server restarts.

The record

CVE
CVE-2026-43678
Published
Aug 20, 2026
Updated
Aug 20, 2026
Vendor
Apple
Product
SwiftNIO
Classifications
CWE-770, CWE-20, CWE-190, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 20, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 20, 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <2.101.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Apple · SwiftNIOversion=0 <2.101.0

Published CVSS scores

7.5GitHub Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
5.3CISA ADP VulnrichmentCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-770Allocation of Resources Without Limits or Throttling
CWE-20Improper Input Validation
CWE-190Integer Overflow or Wraparound
T1499Endpoint Denial of Service

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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