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CVE-2026-27459— pyOpenSSL DTLS cookie callback buffer overflow

Quick assessment

Affected
pyca pyopenssl
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

pyOpenSSL是Python Cryptographic Authority开源的一个Python的OpenSSL库封装工具。 pyOpenSSL 22.0.0至26.0.0之前版本存在安全漏洞，该漏洞源于set_cookie_generate_callback返回的cookie值过长导致缓冲区溢出。

CVSS 7.2 · High EPSS 0.75% · P55

Possible ATT&CK Techniques 1 AI

T1203 · Exploitation for Client Execution

Affected Version Matrix 1

VendorProduct Version RangeStatus
pyca pyopenssl >= 22.0.0, < 26.0.0 affected
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I. Basic Information for CVE-2026-27459

Vulnerability Information
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Vulnerability Title
pyOpenSSL DTLS cookie callback buffer overflow
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:U
Source: CVE Program / CVE List V5
Vulnerability Type
未进行输入大小检查的缓冲区拷贝(传统缓冲区溢出)
Source: CVE Program / CVE List V5
Vulnerability Title
pyOpenSSL 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
pyOpenSSL是Python Cryptographic Authority开源的一个Python的OpenSSL库封装工具。 pyOpenSSL 22.0.0至26.0.0之前版本存在安全漏洞，该漏洞源于set_cookie_generate_callback返回的cookie值过长导致缓冲区溢出。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
pyca pyopenssl >= 22.0.0, < 26.0.0 -

II. Public POCs for CVE-2026-27459

# POC Description Source Link Shenlong Link
AI-Generated POC Verified env Premium
Qwen3.6-35B-A3B · 7975 chars
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Vulnerability reproduction recording (real sandbox build + trigger, exclusive)
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Trigger conditions & impact
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III. Intelligence Information for CVE-2026-27459

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Patches & Fixes for CVE-2026-27459 (1)

Vendor Advisories for CVE-2026-27459 (1)

Other References for CVE-2026-27459 (1)

IV. Related Vulnerabilities

Same product: pyopenssl
Same vendor: pyca
Same weakness: CWE-120