Critical severity · published Mar 17, 2026
CVE-2026-27459
pyOpenSSL DTLS cookie callback buffer overflow
9.8
CVSS
0.7%
EPSS
No
On KEV
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 vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
High
Integrity
High
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.7% · higher than 54% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
PY
pyopenssl · pyca
>= 22.0.0, < 26.0.0 · source: vendor, NVD
EI
Exploit Intelligence · Red Hat
All versions, or not specified · source: CISA
R4
RHUI 4 for RHEL 8 · Red Hat
All versions, or not specified · source: CISA
RH
Red Hat Ansible Automation Platform 2 · Red Hat
All versions, or not specified · source: CISA
RH
Red Hat Ansible Automation Platform 2.5 · Red Hat
All versions, or not specified · source: CISA
RH
Red Hat Ansible Automation Platform 2.5 for RHEL 8 · Red Hat
All versions, or not specified · source: CISA
RH
Red Hat Ansible Automation Platform 2.5 for RHEL 9 · Red Hat
All versions, or not specified · source: CISA
RH
Red Hat Ansible Automation Platform 2.6 · Red Hat
All versions, or not specified · source: CISA
RH
Red Hat Ansible Automation Platform 2.6 for RHEL 9 · Red Hat
All versions, or not specified · source: CISA
RH
Red Hat Ansible Automation Platform 2.7 · Red Hat
All versions, or not specified · source: CISA
RH
Red Hat Ansible Automation Platform Ansible Core 2 · Red Hat
All versions, or not specified · source: CISA
RH
Red Hat Ceph Storage 7 · Red Hat
All versions, or not specified · source: CISA
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-27459
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-27459
Release Notes
https://github.com/pyca/pyopenssl/blob/358cbf29c4e364c59930e53a270116249581eaa3/CHANGELOG.rst
Patch
https://github.com/pyca/pyopenssl/commit/57f09bb4bb051d3bc2a1abd36e9525313d5cd408
Vendor Advisory
https://github.com/pyca/pyopenssl/security/advisories/GHSA-5pwr-322w-8jr4
access.redhat.com
https://access.redhat.com/errata/RHSA-2026:10754
access.redhat.com
https://access.redhat.com/errata/RHSA-2026:11856
access.redhat.com
https://access.redhat.com/errata/RHSA-2026:11916
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