OpenSSL TLS Client Double-Free in OCSP Stapled Response Checking
CVE-2026-35188 is a double-free vulnerability in the OpenSSL TLS client certificate verification path when processing a crafted OCSP stapled response delivered by a server via the TLS status_request extension. When OCSP stapling is enabled on the client, a malicious server can send a specially crafted stapled OCSP response that triggers a double-free during stapled-response validation/checking. The flaw affects OpenSSL 4.0.0 before 4.0.1 and 3.6.0 before 3.6.3. The vulnerable code is outside the OpenSSL FIPS module boundary, and no FIPS modules are affected.
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Impact, mitigation & remediation
What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.
Impact
What an attacker gets, and what they’ve been doing with it.
Mitigation
If you can’t patch tonight, do this now.
Remediation
Patch, then assume compromise.
Exploits
No public exploits tracked yet. Mallory keeps watching.
No public exploit code observed for this vulnerability.
Affected products & vendors
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
Recent activity
3 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
An OpenSSL double-free vulnerability during OCSP stapling/certificate status evaluation that can be triggered by a malicious external server, leading primarily to application crash.
A moderate OpenSSL double-free vulnerability in TLS client OCSP stapling response handling that may cause denial of service and potentially code execution in complex environments.
The version that knows your environment.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.