CVE-2020-12823Public exploit

Local client crash via reused certificate length

Published May 12, 2020 · Updated Aug 4, 2024

Buffer overflow in OpenConnect 8.09 allows local users to crash the VPN client through an overlong certificate distinguished name. In get_cert_name in gnutls.c, a failed name lookup replaces the 80-byte buffer length with a larger required size, which a subsequent lookup reuses to write past the buffer. The flaw is reachable only with a local certificate controlled by the same user, and the demonstrated consequence is process termination from stack corruption.

CVSS severity9.8
Critical
EPSS probability4.62%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Buffer overflow in OpenConnect 8.09 allows local users to crash the VPN client through an overlong certificate distinguished name. In get_cert_name in gnutls.c, a failed name lookup replaces the 80-byte buffer length with a larger required size, which a subsequent lookup reuses to write past the buffer. The flaw is reachable only with a local certificate controlled by the same user, and the demonstrated consequence is process termination from stack corruption.

The record

CVE
CVE-2020-12823
Published
May 12, 2020
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-120, T1499.004
Attack vector
local
Privileges
Unavailable

Timeline

How it unfolded

  1. May 12, 2020CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectorlocal
Required privilegesUnavailable in this record.

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
7.5NIST NVDAV:N/AC:L/Au:N/C:P/I:P/A:P

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

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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)
Vectorlocal
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
T1499.004Application or System Exploitation

Public exploit references

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Technologies

Your stack

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Your stack

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