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CVE-2026-84783VulnerabilityPublished

Issue summary: The first concurrent use of the same X.509 certificate by several threads may cause its cached

Source GCVE Database

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Not known to be exploited · CVSS 7.5 High · fixed in 4.0.3 : patch use by another thread. soon.

Data as of 13 Nov 2026, 23:54 UTC

CVSS 3.1 base score
7.5High
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.2% chance of exploitation in 30 days – higher than 21% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Affects
use by another thread. prior to 4.0.3
Patch
Available – fixed in 4.0.3
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 29 Sep 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 14 Nov 2026.

What to do

AI-suggested

Users of OpenSSL 4.0 should upgrade to OpenSSL 4.0.3, where this issue is fixed. Earlier OpenSSL versions are not affected. No other mitigation is required.

Description

OpenSSL 4.0 has a use-after-free vulnerability triggered by concurrent decoding of the same X.509 certificate's extensions by multiple threads. This can cause a multi-threaded TLS client or server to crash, resulting in a denial of service. The issue arises because cached extension data is freed while still in use by another thread. Versions prior to 4.0.3 are affected, while earlier OpenSSL versions are not vulnerable.

References

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