CVE-2026-33307Network attack vector

Unauthenticated server crash via oversized certificate chain

Published Mar 24, 2026 · Updated Mar 24, 2026

Stack-based buffer overflow in mod_gnutls before 0.12.3 allows remote attackers to crash Apache HTTPD via a long client certificate chain. The mgs_cert_verify function passes an unchecked certificate count beyond the fixed x509 pointer array and calls gnutls_x509_crt_init on an out-of-bounds element. Exploitation requires client-certificate verification; the default GnuTLSClientVerify ignore configuration is unaffected, and the observed consequence is a segmentation fault rather than attacker-controlled stack data.

CVSS severity7.5
High
EPSS probability0.34%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stack-based buffer overflow in mod_gnutls before 0.12.3 allows remote attackers to crash Apache HTTPD via a long client certificate chain. The mgs_cert_verify function passes an unchecked certificate count beyond the fixed x509 pointer array and calls gnutls_x509_crt_init on an out-of-bounds element. Exploitation requires client-certificate verification; the default GnuTLSClientVerify ignore configuration is unaffected, and the observed consequence is a segmentation fault rather than attacker-controlled stack data.

The record

CVE
CVE-2026-33307
Published
Mar 24, 2026
Updated
Mar 24, 2026
Vendor
airtower-luna
Product
mod_gnutls
Classifications
CWE-121, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 24, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 24, 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=< 0.12.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

airtower-luna · mod_gnutlsversion=< 0.12.3

Published CVSS scores

7.5GitHub, Inc.CVSS: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-121Stack-based Buffer Overflow
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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