CVE-2026-63075 Details
Issue summary: When OpenSSL processes QUIC traffic from a peer that repeatedly
sends ack-eliciting packets while not acknowledging ACK-only responses, the
QUIC stack can retain ACK-only packet metadata for the lifetime of the
connection.

Impact summary: A remote peer that can complete a QUIC handshake can
cause connection-scoped memory growth which may lead to Denial of Service
through memory exhaustion, especially with sustained traffic or many concurrent
QUIC connections.

CWE: CWE-770: Allocation of Resources Without Limits or Throttling

Description: When the OpenSSL QUIC stack sends an ACK-only packet,
there is no requirement by the QUIC protocol that the peer will acknowledge
that ACK-only packet (i.e. it is itself not ack-eliciting). However, the OpenSSL
implementation stores the metadata about the ACK frames regardless.
In and of itself that's ok, but if a malicious peer establishes a connection, and
then drives the connection such that ACK-only packets are forced from the
OpenSSL implementation peer (i.e., by sending numerous PING frames),
and then withholding any subsequent acks for ack-eliciting data, like
legitimate data, said malicious peer can force inappropriate memory growth
on the OpenSSL peer, potentially leading to a Denial of Service.

The fix is to ensure that we account for the transmission of the ACK-only
packet in the packet histories high and low watermark without actually storing
the ACK-only packet metadata itself.

FIPS impact: no
The OpenSSL FIPS module is not affected as the QUIC code is
outside the FIPS module boundary.
View at NVD
Exploit prediction scoring system (EPSS) score for CVE-2026-63075
EPSS (Exploit Prediction Scoring System): EPSS predicts the likelihood that a vulnerability will be exploited in the wild. A higher percentage means a greater chance of an exploit occurring. The EPSS model produces a probability score between 0 and 1 (0 and 100%).
0.57 Probability of exploitation activity being observed over the next 30 days (46th percentile)
CVSS score for CVE-2026-63075
CVSS (Common Vulnerability Scoring System): An open framework owned and managed by FIRST.Org, Inc. that assigns a numerical score from 0 to 10 to software vulnerabilities to indicate their severity.
7.5 High
Products affected by CVE-2026-63075
OpenSSL 3.4.0
OpenSSL 3.4.1
OpenSSL 3.5.0
OpenSSL 3.6.2
OpenSSL 3.5.1
DVE Score by Bitsight AI
DVE scores complement traditional static scoring systems like CVSS with Bitsight AI powered real-time threat intelligence and underground cyber criminal activity so that security teams can reduce alert fatigue and focus on vulnerabilities most likely to be exploited.
Low
More on DVE scores

CVE-2026-63075 Global Footprint

Top 10 Identified Countries

Country Observations Percentage
US 48,001 34.62%
DE 14,668 10.58%
JP 12,051 8.69%
CA 5,190 3.74%
DK 4,934 3.56%
GB 4,774 3.44%
FR 4,010 2.89%
IN 3,873 2.79%
NL 3,671 2.65%
IE 3,504 2.53%

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CVE-2026-63075 Industry Footprint

Top 10 Identified Industries

*Service provider organizations (typically Technology and Telecommunications) are disproportionally represented in the results given their upstream ownership of end-user infrastructure. See our FAQs.

Industry* Observations Percentage
Technology 76,807 76.94%
Telecommunications 11,546 11.57%
Education 5,419 5.43%
Government/Politics 1,278 1.28%
Energy/Resources 1,107 1.11%
Media/Entertainment 694 0.70%
Business Services 515 0.52%
Manufacturing 394 0.39%
Finance 325 0.33%
Utilities 318 0.32%

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