Issue summary: The first concurrent use of the same X.509 certificate by several threads may cause its cached
Source GCVE Database
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
- 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:HExploitation evidence
Disclosed: evidence found.
CVE published 29 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by 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.