Summary
rust-openssl has undefined behavior in X509Ref::ocsp_responders for certificates with non-UTF-8 OCSP URLs
X509Ref::ocsp_responders returns OCSP responder URLs from a certificate's AIA extension as OpensslString, whose Deref<Target = str> wraps the raw bytes with str::from_utf8_unchecked. OpenSSL does not enforce that the underlying IA5String is ASCII, so a certificate with non-UTF-8 bytes in its OCSP accessLocation causes safe Rust code to construct a &str that violates the UTF-8 invariant, resulting in undefined behavior.
Impact
The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths. Typical impact: varies by context: data corruption, logic bypass, or denial of service.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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Frequently Asked Questions
- What is CVE-2026-42327? CVE-2026-42327 is a high-severity improper input validation vulnerability in openssl (rust), affecting versions >= 0.9.7, < 0.10.79. It is fixed in 0.10.79. The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths.
- Which versions of openssl are affected by CVE-2026-42327? openssl (rust) versions >= 0.9.7, < 0.10.79 is affected.
- Is there a fix for CVE-2026-42327? Yes. CVE-2026-42327 is fixed in 0.10.79. Upgrade to this version or later.
- Is CVE-2026-42327 exploitable, and should I be worried? Whether CVE-2026-42327 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-42327 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-42327? Upgrade
opensslto 0.10.79 or later.