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
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-35188
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-35188
Patch
https://github.com/openssl/openssl/commit/131145d25659e8749a9ed1afb383484854cffb78
Patch
https://github.com/openssl/openssl/commit/78d0154cffda03aaaac63a087cc523a6b35fa8fd
Vendor Advisory
https://openssl-library.org/news/secadv/20260609.txt
More from OpenSSL
7.5
CVE-2014-0160
OpenSSL Information Disclosure Vulnerability
9.8
CVE-2026-63073
Untrusted Sender DN Used as Format String in CMP Response Validation
9.8
CVE-2026-31789
Heap Buffer Overflow in Hexadecimal Conversion
9.8
CVE-2022-2274
RSA implementation bug in AVX512IFMA instructions
9.8
CVE-2021-3711
SM2 Decryption Buffer Overflow
