Summary
pyOpenSSL DTLS cookie callback buffer overflow
If a user provided callback to set_cookie_generate_callback returned a cookie value greater than 256 bytes, pyOpenSSL would overflow an OpenSSL provided buffer.
Cookie values that are too long are now rejected.
Impact
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.
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. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-27459? CVE-2026-27459 is a high-severity security vulnerability in pyopenssl (pip), affecting versions >= 22.0.0, < 26.0.0. It is fixed in 26.0.0.
- Which versions of pyopenssl are affected by CVE-2026-27459? pyopenssl (pip) versions >= 22.0.0, < 26.0.0 is affected.
- Is there a fix for CVE-2026-27459? Yes. CVE-2026-27459 is fixed in 26.0.0. Upgrade to this version or later.
- Is CVE-2026-27459 exploitable, and should I be worried? Whether CVE-2026-27459 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-2026-27459 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-2026-27459? Upgrade
pyopensslto 26.0.0 or later.