pyOpenSSL CVE-2026-27459: Buffer Overflow via cookie callback (22.0.0-26.0.0)
CVE-2026-27459 Published on March 17, 2026

pyOpenSSL DTLS cookie callback buffer overflow
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.

NVD

Vulnerability Analysis

CVE-2026-27459 can be exploited with network access, and does not require authorization privileges or user interaction. This vulnerability is consided to have a high level of attack complexity. The potential impact of an exploit of this vulnerability is considered to be very high.

Attack Vector:
NETWORK
Attack Complexity:
HIGH
Privileges Required:
NONE
User Interaction:
NONE
Scope:
UNCHANGED
Confidentiality Impact:
HIGH
Integrity Impact:
HIGH
Availability Impact:
HIGH

Weakness Type

What is a Classic Buffer Overflow Vulnerability?

The program copies an input buffer to an output buffer without verifying that the size of the input buffer is less than the size of the output buffer, leading to a buffer overflow. A buffer overflow condition exists when a program attempts to put more data in a buffer than it can hold, or when a program attempts to put data in a memory area outside of the boundaries of a buffer. The simplest type of error, and the most common cause of buffer overflows, is the "classic" case in which the program copies the buffer without restricting how much is copied. Other variants exist, but the existence of a classic overflow strongly suggests that the programmer is not considering even the most basic of security protections.

CVE-2026-27459 has been classified to as a Classic Buffer Overflow vulnerability or weakness.


Products Associated with CVE-2026-27459

You can be notified by email with stack.watch whenever vulnerabilities like CVE-2026-27459 are published in these products:

Canonical Ubuntu Linux
 
Red Hat Ansible Automation Platform
 
Red Hat Ansible Automation Platform Developer
 
Red Hat Ansible Automation Platform Inside
 
Red Hat Rhui
 
Red Hat Satellite
 
Red Hat Satellite Capsule
 
Red Hat Satellite Utils
 
Red Hat Satellite Maintenance
 
Red Hat Hummingbird
 
Red Hat Quay
 
Red Hat Trusted Artifact Signer
 
Red Hat Ansible Core
 
Red Hat Openshift Ai
 
Red Hat Enterprise Linux (RHEL)
 
Red Hat Openshift
 
Red Hat Openstack
 

Affected Versions

pyca pyopenssl: Red Hat Ansible Automation Platform 2.5 for RHEL 8: Red Hat Ansible Automation Platform 2.5 for RHEL 9: Red Hat Ansible Automation Platform 2.6 for RHEL 9: Red Hat Ansible Automation Platform 2.6 for RHEL 9: Red Hat Satellite 6.16 for RHEL 8: Red Hat Satellite 6.16 for RHEL 9: Red Hat Satellite 6.17 for RHEL 9: Red Hat Satellite 6.18 for RHEL 9: Red Hat RHUI 4 for RHEL 8: Red Hat Ansible Automation Platform 2.5: Red Hat Ansible Automation Platform 2.5: Red Hat Ansible Automation Platform 2.6: Red Hat Ansible Automation Platform 2.6: Red Hat Ansible Automation Platform 2.6: Red Hat Ansible Automation Platform 2.6: Red Hat Ansible Automation Platform 2.6: Red Hat Ansible Automation Platform 2.6: Red Hat Hardened Images: Red Hat Quay 3.1: Red Hat Quay 3.12: Red Hat Quay 3.14: Red Hat Quay 3.15: Red Hat Quay 3.16: Red Hat Quay 3.17: Red Hat Quay 3.9: Red Hat Trusted Artifact Signer 1.4: Red Hat Ansible Automation Platform 2: Red Hat Ansible Automation Platform 2: Red Hat Ansible Automation Platform 2: Red Hat Ansible Automation Platform 2: Red Hat Ansible Automation Platform 2: Red Hat Ansible Automation Platform Ansible Core 2: Red Hat Ansible Automation Platform Ansible Core 2: Red Hat Ansible Automation Platform Ansible Core 2: Red Hat Ansible Automation Platform Ansible Core 2: Red Hat Enterprise Linux 6: Red Hat Enterprise Linux 7: Red Hat Enterprise Linux 8: Red Hat OpenShift AI (RHOAI): Red Hat OpenShift AI (RHOAI): Red Hat OpenShift Container Platform 4: Red Hat OpenStack Platform 17.1: Red Hat OpenStack Platform 18.0: Red Hat Satellite 6: Red Hat Satellite 6:

Exploit Probability

EPSS
0.50%
Percentile
38.80%

EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.