CVE-2026-84783Network attack vectorHinoki check available

Process crash via X.509 extension cache race

Published Sep 29, 2026 · Updated Sep 29, 2026

Use-after-free in OpenSSL 4.0.0 through 4.0.2 allows remote attackers to crash multithreaded TLS clients or client-authenticating servers. The X.509v3 extension cache in ossl_x509v3_cache_extensions() lets competing threads replace and free cached values after another thread receives pointers to them. The race requires simultaneous first-time chain verification against the same shared trusted CA certificate; peer-supplied certificates alone do not trigger it.

CVSS severityUnavailable
Unscored
EPSS probability0.23%
Next 30 days · Oct 19, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

Use-after-free in OpenSSL 4.0.0 through 4.0.2 allows remote attackers to crash multithreaded TLS clients or client-authenticating servers. The X.509v3 extension cache in ossl_x509v3_cache_extensions() lets competing threads replace and free cached values after another thread receives pointers to them. The race requires simultaneous first-time chain verification against the same shared trusted CA certificate; peer-supplied certificates alone do not trigger it.

The record

CVE
CVE-2026-84783
Published
Sep 29, 2026
Updated
Sep 29, 2026
Vendor
OpenSSL Project
Product
OpenSSL
Classifications
CWE-416, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 29, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 29, 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=4.0.0 <4.0.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

OpenSSL Project · OpenSSLversion=4.0.0 <4.0.3

Published CVSS scores

No CVSS assessment is available in this record.

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.

Activity data is delayed. The latest report is Sep 28, 2026.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 22, 2026Sep 28, 2026
Latest reporting daySep 28, 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
T1499.004Application or System Exploitation

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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