CVE-2026-35188
CVE-2026-35188 is a medium-severity vulnerability in Openssl with a CVSS 3.x base score of 5.0. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-415.
Key facts
- Severity: Medium (CVSS 3.x base score 5.0)
- EPSS exploit prediction: 0% (16th percentile)
- Actively exploited: Not listed in CISA KEV
- EU (EUVD) id: EUVD-2026-35480
- Weakness: CWE-415
- Affected product: Openssl
- Published:
- Last modified:
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.
Frequently asked questions
- What is CVE-2026-35188?
- 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.
- How severe is CVE-2026-35188?
- CVE-2026-35188 has a CVSS 3.x base score of 5.0, rated medium severity. It is exploitable over network with high attack complexity, requires low privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability low.
- Is CVE-2026-35188 being actively exploited?
- It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (16th percentile), an estimate of the probability of exploitation in the next 30 days.
- What products are affected by CVE-2026-35188?
- CVE-2026-35188 primarily affects Openssl. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
- How do I fix CVE-2026-35188?
- Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
- Does CVE-2026-35188 have an EU (EUVD) identifier?
- Yes. CVE-2026-35188 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-35480.
- When was CVE-2026-35188 published?
- CVE-2026-35188 was published on 2026-06-09 and last updated on 2026-06-17.
References
- https://github.com/openssl/openssl/commit/131145d25659e8749a9ed1afb383484854cffb78
- https://github.com/openssl/openssl/commit/78d0154cffda03aaaac63a087cc523a6b35fa8fd
- https://openssl-library.org/news/secadv/20260609.txt
Affected products (2)
- cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:*
- cpe:2.3:a:openssl:openssl:4.0.0:-:*:*:*:*:*:*
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