CVE-2026-63075Network attack vector

Remote memory exhaustion via retained ACK metadata

Published Aug 25, 2026 · Updated Aug 25, 2026

Resource exhaustion in affected OpenSSL 3.4, 3.5, 3.6, and 4.0 releases allows remote attackers to exhaust memory via QUIC traffic. The QUIC transmit path retains ACK-only packet metadata for the connection lifetime even though peers need not acknowledge those packets. A peer that completes a QUIC handshake can force repeated ACK-only responses with PING frames and withhold later acknowledgments, causing a service interrupt through connection-scoped memory growth.

CVSS severity7.5
High
EPSS probability0.48%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Resource exhaustion in affected OpenSSL 3.4, 3.5, 3.6, and 4.0 releases allows remote attackers to exhaust memory via QUIC traffic. The QUIC transmit path retains ACK-only packet metadata for the connection lifetime even though peers need not acknowledge those packets. A peer that completes a QUIC handshake can force repeated ACK-only responses with PING frames and withhold later acknowledgments, causing a service interrupt through connection-scoped memory growth.

The record

CVE
CVE-2026-63075
Published
Aug 25, 2026
Updated
Aug 25, 2026
Vendor
OpenSSL Project
Product
OpenSSL
Classifications
CWE-770, T1499.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 25, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 25, 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=3.4.0 <3.4.7
  2. Affected versionversion=3.5.0 <3.5.8
  3. Affected versionversion=3.6.0 <3.6.4
  4. Affected versionversion=4.0.0 <4.0.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

OpenSSL Project · OpenSSLversion=3.4.0 <3.4.7; version=3.5.0 <3.5.8; version=3.6.0 <3.6.4; version=4.0.0 <4.0.2

Published CVSS scores

7.5CISA ADP VulnrichmentCVSS: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 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 exploitUnconfirmed

Weakness, pattern, technique

CWE-770Allocation of Resources Without Limits or Throttling
T1499.002Service Exhaustion Flood

Public exploit references

No public exploit references are available in this record.

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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