Improper Certificate Validation in cURL - CVE-2026-87866
Published: October 14, 2026
Vulnerability identifier: #VU155680
CSH Severity: Medium
CVSS v4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-87866
CWE-ID: CWE-295
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to bypass public-key pinning.
The vulnerability exists due to improper certificate validation in libcurl's public-key pinning certificate parser when re-parsing a TLS peer certificate after the handshake. A remote attacker can present a malformed certificate with a manipulated validity length field to bypass public-key pinning.
Exploitation requires libcurl to be built with wolfSSL and relies on a wolfSSL bug that accepts the malformed certificate. The curl command-line tool is not affected.
Affected software
cURL
How to mitigate CVE-2026-87866
Install security update from vendor's website.
cURL - update to 8.23.0