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9.8
CRITICAL CVSS 3.1
CVE-2026-27459
pyOpenSSL DTLS cookie callback buffer overflow
Overview
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.

Details
INFO

Published Date :

March 18, 2026, 12:16 a.m.

Last Modified :

March 25, 2026, 4:41 p.m.

Remotely Exploit :

Yes !

Source :

[email protected]
Impact
Affected Products

The following products are affected by CVE-2026-27459 vulnerability. Even if cvefeed.io is aware of the exact versions of the products that are affected, the information is not represented in the table below.

ID Vendor Product Action
1 Pyopenssl pyopenssl
: Total Affected Vendor : 1 | Products : 1
Scoring
CVSS Scores
The Common Vulnerability Scoring System is a standardized framework for assessing the severity of vulnerabilities in software and systems. We collect and displays CVSS scores from various sources for each CVE.
Score Version Severity Vector Exploitability Score Impact Score Source
CVSS 3.1 CRITICAL [email protected]
CVSS 4.0 HIGH [email protected]
Solution
Update pyOpenSSL to version 26.0.0 or later to fix buffer overflow.
  • Update pyOpenSSL to version 26.0.0 or later.
  • Ensure cookie values do not exceed 256 bytes.
Public PoC/Exploit Available at Github

CVE-2026-27459 has a 2 public PoC/Exploit available at Github. Go to the Public Exploits tab to see the list.

References
References to Advisories, Solutions, and Tools

Here, you will find a curated list of external links that provide in-depth information, practical solutions, and valuable tools related to CVE-2026-27459.

URL Resource
https://github.com/pyca/pyopenssl/blob/358cbf29c4e364c59930e53a270116249581eaa3/CHANGELOG.rst Release Notes
https://github.com/pyca/pyopenssl/commit/57f09bb4bb051d3bc2a1abd36e9525313d5cd408 Patch
https://github.com/pyca/pyopenssl/security/advisories/GHSA-5pwr-322w-8jr4 Vendor Advisory
CWE - Common Weakness Enumeration

While CVE identifies specific instances of vulnerabilities, CWE categorizes the common flaws or weaknesses that can lead to vulnerabilities. CVE-2026-27459 is associated with the following CWEs:

Common Attack Pattern Enumeration and Classification (CAPEC)

Common Attack Pattern Enumeration and Classification (CAPEC) stores attack patterns, which are descriptions of the common attributes and approaches employed by adversaries to exploit the CVE-2026-27459 weaknesses.

CAPEC-8: Buffer Overflow in an API Call Buffer Overflow in an API Call CAPEC-9: Buffer Overflow in Local Command-Line Utilities Buffer Overflow in Local Command-Line Utilities CAPEC-10: Buffer Overflow via Environment Variables Buffer Overflow via Environment Variables CAPEC-14: Client-side Injection-induced Buffer Overflow Client-side Injection-induced Buffer Overflow CAPEC-24: Filter Failure through Buffer Overflow Filter Failure through Buffer Overflow CAPEC-42: MIME Conversion MIME Conversion CAPEC-44: Overflow Binary Resource File Overflow Binary Resource File CAPEC-45: Buffer Overflow via Symbolic Links Buffer Overflow via Symbolic Links CAPEC-46: Overflow Variables and Tags Overflow Variables and Tags CAPEC-47: Buffer Overflow via Parameter Expansion Buffer Overflow via Parameter Expansion CAPEC-67: String Format Overflow in syslog() String Format Overflow in syslog() CAPEC-92: Forced Integer Overflow Forced Integer Overflow CAPEC-100: Overflow Buffers Overflow Buffers

We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).

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Results are limited to the first 15 repositories due to potential performance issues.

The following list is the news that have been mention CVE-2026-27459 vulnerability anywhere in the article.

Results are limited to the first 20 news articles due to potential performance issues.

The following table lists the changes that have been made to the CVE-2026-27459 vulnerability over time.

Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.

  • Reanalysis by [email protected]

    Mar. 25, 2026

    Action Type Old Value New Value
    Changed CPE Configuration OR *cpe:2.3:a:pyopenssl:pyopenssl:*:*:*:*:*:*:*:* versions from (including) 22.0.0 up to (including) 26.0.0 OR *cpe:2.3:a:pyopenssl:pyopenssl:*:*:*:*:*:*:*:* versions from (including) 22.0.0 up to (excluding) 26.0.0
  • Initial Analysis by [email protected]

    Mar. 23, 2026

    Action Type Old Value New Value
    Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
    Added CPE Configuration OR *cpe:2.3:a:pyopenssl:pyopenssl:*:*:*:*:*:*:*:* versions from (including) 22.0.0 up to (including) 26.0.0
    Added Reference Type GitHub, Inc.: https://github.com/pyca/pyopenssl/blob/358cbf29c4e364c59930e53a270116249581eaa3/CHANGELOG.rst Types: Release Notes
    Added Reference Type GitHub, Inc.: https://github.com/pyca/pyopenssl/commit/57f09bb4bb051d3bc2a1abd36e9525313d5cd408 Types: Patch
    Added Reference Type GitHub, Inc.: https://github.com/pyca/pyopenssl/security/advisories/GHSA-5pwr-322w-8jr4 Types: Vendor Advisory
  • New CVE Received by [email protected]

    Mar. 18, 2026

    Action Type Old Value New Value
    Added 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.
    Added CVSS V4.0 AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:U/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
    Added CWE CWE-120
    Added Reference https://github.com/pyca/pyopenssl/blob/358cbf29c4e364c59930e53a270116249581eaa3/CHANGELOG.rst
    Added Reference https://github.com/pyca/pyopenssl/commit/57f09bb4bb051d3bc2a1abd36e9525313d5cd408
    Added Reference https://github.com/pyca/pyopenssl/security/advisories/GHSA-5pwr-322w-8jr4
EPSS is a daily estimate of the probability of exploitation activity being observed over the next 30 days. Following chart shows the EPSS score history of the vulnerability.
CVSS
Vulnerability Scoring Details
Base CVSS Score: 7.2
Attack Vector
Attack Complexity
Attack Requirements
Privileges Required
User Interaction
VS Confidentiality
VS Integrity
VS Availability
SS Confidentiality
SS Integrity
SS Availability
Base CVSS Score: 9.8
Attack Vector
Attack Complexity
Privileges Required
User Interaction
Scope
Confidentiality Impact
Integrity Impact
Availability Impact