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CVE-2026-27459

pyOpenSSL DTLS cookie callback buffer overflow

Published: Mar 17, 2026Updated: Mar 25, 2026 Sources: CVE List NVD GHSACWE-120
NVD MITRE
9.8CVSSCRITICAL
EPSS Score
0.5%
Top 61.2%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Patch Available

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 Breakdown

AV:NAC:LPR:NUI:NS:UC:HI:HA:H
Exploitability
AV:NAttack Vector
Network
AC:LAttack Complexity
Low
PR:NPrivileges Required
None
UI:NUser Interaction
None
Scope
S:UScope
Unchanged
Impact
C:HConfidentiality
High
I:HIntegrity
High
A:HAvailability
High
Open in CVSS calculator →

Weaknesses

CWE-120

Affected Products

pyopensslpyopenssl
Library
OSS Libraries / generic-library
pyopensslpyca
Library
OSS Libraries / pypi
pyopensslPyPIOSS Libraries
pyopenssloss-projectOSS Librariesaka pyopenssl, pyopenssl
pycaoss-projectGBOSS Librariesaka pyca/cryptography, py ca, pyca
pypipackage-ecosystemOSS Libraries

Attack Graph

Products CVE Techniques Tactics

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Exploitability

Official Patch Available

MITRE ATT&CK

2 techniques
Initial Access
Privilege Escalation
View detailed technique mapping

References

https://github.com/pyca/pyopenssl/blob/358cbf29c4e364c59930e53a270116249581eaa3/CHANGELOG.rst
github.com
https://github.com/pyca/pyopenssl/commit/57f09bb4bb051d3bc2a1abd36e9525313d5cd408
github.com
https://github.com/pyca/pyopenssl/security/advisories/GHSA-5pwr-322w-8jr4
github.com
and 2 more references View all →

Timeline

Published
Mar 17, 2026
Last Updated
Mar 25, 2026

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