Buffer overflow in pyopenssl - CVE-2026-27459

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Main Vulnerability Database Vulnerabilities #VU144104

Buffer overflow in pyopenssl - CVE-2026-27459

Published: August 18, 2026


Vulnerability identifier: #VU144104
CSH Severity: High
CVSS v4: 9.3 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-27459
CWE-ID: CWE-120
Exploitation vector: Remote access
Exploit availability: No public exploit available

Vulnerability details

The vulnerability allows a remote attacker to execute arbitrary code on the target system.

The vulnerability exists because the callback provided to `set_cookie_generate_callback` returned a cookie value greater than 256 bytes, causing pyOpenSSL to overflow an OpenSSL-provided buffer. A remote attacker can pass specially crafted data to the application, trigger a buffer overflow and execute arbitrary code on the target system.


Affected software

pyopenssl
Fedora
rust-cryptoki-sys
rust-wycheproof
rust-cryptoki
rust-asn1
rust-asn1_derive
kryoptic
pyOpenSSL
python-cryptography

How to mitigate CVE-2026-27459

Install updates from vendor's website.

pyopenssl - update to 26.1.0
rust-cryptoki-sys - update to 0.5.0-2.fc43
rust-wycheproof - update to 0.6.0-1.fc43
rust-cryptoki - update to 0.12.0-2.fc43
rust-asn1 - update to 0.22.0-1.fc43
rust-asn1_derive - update to 0.22.0-1.fc43
kryoptic - update to 1.5.0-2.fc43
pyOpenSSL - update to 26.0.0-1.fc43
python-cryptography - update to 46.0.5-1.fc43

External References

Related Security Bulletins