CVE-2021-20232Network attack vector

Client memory corruption via stale PSK binder pointer

Published Mar 12, 2021 · Updated Dec 3, 2025

Use-after-free in GnuTLS before 3.7.1 allows remote attackers to crash a TLS 1.3 client during a crafted resumed handshake. client_send_params keeps a pointer into extdata, then _gnutls_buffer_append_prefix can reallocate that buffer before compute_psk_binder dereferences the stale pointer. Triggering requires TLS 1.3, a large ClientHello, and a HelloRetryRequest in a resumed session previously negotiated with large FFDHE parameters; memory corruption can crash the client.

CVSS severity9.8
Critical
EPSS probability3.44%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Use-after-free in GnuTLS before 3.7.1 allows remote attackers to crash a TLS 1.3 client during a crafted resumed handshake. client_send_params keeps a pointer into extdata, then _gnutls_buffer_append_prefix can reallocate that buffer before compute_psk_binder dereferences the stale pointer. Triggering requires TLS 1.3, a large ClientHello, and a HelloRetryRequest in a resumed session previously negotiated with large FFDHE parameters; memory corruption can crash the client.

The record

CVE
CVE-2021-20232
Published
Mar 12, 2021
Updated
Dec 3, 2025
Vendor
GnuTLS Project
Product
GnuTLS
Classifications
CWE-416, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 12, 2021CVE publishedPublication date reported by the CVE source.
  2. Dec 3, 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?

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  1. Affected versionversion=gnutls 3.7.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

GnuTLS Project · GnuTLSversion=gnutls 3.7.1

Published CVSS scores

9.8UbuntuCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-416Use After Free
T1499Endpoint Denial of Service

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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