CVE-2026-35188: Double-free When Checking OCSP Stapled Response

Severity: medium (CVSS 5.0 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-06-09 · updated 2026-07-23
Weakness: CWE-415

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.

Affected products

OpenSSL: from 3.6.0 before 3.6.3; 4.0.0 — fixed in 3.6.3

How to fix

Upgrade to a fixed version: OpenSSL 3.6.3. Check the vendor advisory for mitigations.

References

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