CVE-2026-63495Public exploitNetwork attack vector

Memory exhaustion via fragmented frame buffering

Published Aug 20, 2026 · Updated Aug 20, 2026

Resource exhaustion in the WebSocket server in Libevent before 2.2.2-alpha allows remote attackers to interrupt service via fragmented frames. In ws.c, the INCOMPLETE_FRAME path appends each FIN=0 fragment to evws->incomplete_frames and enforces WS_MAX_RECV_FRAME_SZ only per frame, not across the reassembled message. Any client that can complete a WebSocket handshake can keep sending sublimit fragments until the process becomes unresponsive or the host exhausts memory.

CVSS severity7.5
High
EPSS probability0.52%
Next 30 days · Sep 17, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Resource exhaustion in the WebSocket server in Libevent before 2.2.2-alpha allows remote attackers to interrupt service via fragmented frames. In ws.c, the INCOMPLETE_FRAME path appends each FIN=0 fragment to evws->incomplete_frames and enforces WS_MAX_RECV_FRAME_SZ only per frame, not across the reassembled message. Any client that can complete a WebSocket handshake can keep sending sublimit fragments until the process becomes unresponsive or the host exhausts memory.

The record

CVE
CVE-2026-63495
Published
Aug 20, 2026
Updated
Aug 20, 2026
Vendor
Libevent
Product
Libevent
Classifications
CWE-770, CWE-400, T1499.003
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=>= 2.2.0-alpha-dev, < 2.2.2-alpha

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Libevent · Libeventversion=>= 2.2.0-alpha-dev, < 2.2.2-alpha

Published CVSS scores

7.5GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

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 11, 2026Sep 17, 2026
Latest reporting daySep 17, 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-400Uncontrolled Resource Consumption
T1499.003Application Exhaustion Flood

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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