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CVE-2026-27459

Pyopenssl buffer overflow

9.8 CRITICALEPSS 0.88%
  1. Published17 Mar 2026

Description

pyOpenSSL is a Python wrapper around the OpenSSL library. Starting in version 22.0.0 and prior to version 26.0.0, 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. Starting in version 26.0.0, cookie values that are too long are now rejected.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

Pyopenssl≥ 22.0.0 < 26.0.0

Remediation

Fixed in
Pyopenssl≥ 26.0.0

References

and 16 more references

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Frequently asked

Is CVE-2026-27459 being actively exploited?

CVE-2026-27459 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.88%.

How severe is CVE-2026-27459?

CVE-2026-27459 has a CVSS 3.1 base score of 9.8, rated critical. EPSS estimates a 0.88% probability of exploitation.

Which products are affected by CVE-2026-27459?

Affected products include Pyopenssl.

How do I fix CVE-2026-27459?

Upgrade affected software to a fixed version, for example Pyopenssl 26.0.0 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-27459 against the real software inventory on every managed device, as each hourly inventory arrives. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.