CVE-2023-39321Network attack vector

Remote process crash via partial QUIC handshake

Published Sep 8, 2023 · Updated Feb 13, 2025

Denial of service in Go standard library crypto/tls 1.21.0 allows remote attackers to crash QUIC-based processes via partial messages. QUICConn.HandleData uses an incorrect buffered-message size check, passes incomplete data to handlePostHandshakeMessage, and panics when that function reads the missing remainder. The peer must complete a QUIC handshake before sending the fragment; the resulting panic interrupts the affected process without exposing or changing data.

CVSS severity7.5
High
EPSS probability1.36%
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 Go standard library crypto/tls 1.21.0 allows remote attackers to crash QUIC-based processes via partial messages. QUICConn.HandleData uses an incorrect buffered-message size check, passes incomplete data to handlePostHandshakeMessage, and panics when that function reads the missing remainder. The peer must complete a QUIC handshake before sending the fragment; the resulting panic interrupts the affected process without exposing or changing data.

The record

CVE
CVE-2023-39321
Published
Sep 8, 2023
Updated
Feb 13, 2025
Vendor
Go standard library
Product
crypto/tls
Classifications
CWE-400, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 8, 2023CVE publishedPublication date reported by the CVE source.
  2. Feb 13, 2025Record 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=1.21.0-0 <1.21.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Go standard library · crypto/tlsversion=1.21.0-0 <1.21.1

Published CVSS scores

7.5NIST NVDCVSS: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.

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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-400Uncontrolled Resource Consumption
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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