Medium severity · published Jun 9, 2026
CVE-2026-35188
Double-free When Checking OCSP Stapled Response
5.0
CVSS
0.3%
EPSS
No
On KEV
Description
Issue summary: A malicious server can exploit TLS OCSP stapling by delivering a crafted response through the status_request extension, triggering a double-free in the client's certificate verification path. Impact summary: Successful exploitation allows an attacker to corrupt heap memory via a double-free, potentially leading to a Denial of Service or possibly an attacker controlled code execution or other undefined behavior. If OCSP stapling is enabled and the TLS client connects to a malicious server, a crafted OCSP stapled response can trigger a double free in the TLS client when the stapled response is checked. The OCSP stapling is not enabled by default. Reliable code execution through a double-free is technically complex and highly environment-dependent but the Denial of Service impact is straightforward to achieve, warranting Moderate severity. No FIPS modules are affected by this issue as the affected code is outside the OpenSSL FIPS module boundary.
CVSS vector
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:L
Attack vector
Network
Complexity
High
Privileges
Low
User interaction
None
Confidentiality
Low
Integrity
Low
Availability
Low
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 23% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
OP
OpenSSL · OpenSSL
4.0.0 before 4.0.1; 3.6.0 before 3.6.3 · source: vendor, NVD
In the news
VulnerabilityHigh
ZDI-26-425: OpenSSL OCSP Stapling Verification Double Free Remote Code Execution Vulnerability
This vulnerability allows remote attackers to execute arbitrary code on affected installations of OpenSSL. User interaction is required to exploit this vulnerability in that the target must make a request to a malicious server. The ZDI has assigned a CVSS rating of 7.5. The following CVEs are assigned: CVE-2026-35188.
Jul 15, 2026·Zero Day Initiative
Affected product
OP
OpenSSL
OpenSSL
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