NewsSecurity Vulnerabilities

cURL and libcurl verify_certificate Function Improper Certificate Validation Vulnerability [CVE-2016-9952]

CVE Number – CVE-2016-9952

A vulnerability in cURL and libcurl could allow an unauthenticated, remote attacker to bypass security restrictions on a targeted system. The vulnerability is due to improper certificate validation by the verify_certificate function, as defined in the lib/vtls/schannel.c source code file of the affected software. An attacker could exploit this vulnerability by supplying a server certificate that contains a malicious wildcard Subject Alternative Name (SAN) to the targeted system. A successful exploit could allow the attacker to conduct a man-in-the-middle attack. The cURL Project has confirmed the vulnerability and released software updates. 


  • To exploit this vulnerability and conduct a man-in-the-middle attack, the attacker must be positioned between a remote server and the targeted system. The attacker would likely need to be on the same network as the two systems, which may reduce the likelihood of a successful exploit.


  • Administrators are advised to apply the appropriate updates.

    Administrators are advised to allow only trusted users to have network access.

    Administrators are advised to run both firewall and antivirus applications to minimize the potential of inbound and outbound threats.

    Administrators may consider using IP-based access control lists (ACLs) to allow only trusted systems to access the affected systems.

    Administrators can help protect affected systems from external attacks by using a solid firewall strategy.

    Administrators are advised to monitor affected systems.

Vendor Announcements

  • The cURL Project released a security advisory at the following link: CVE-2016-9952

Fixed Software

  • The cURL Project has released a software update at the following link: curl 7.52.0


Duncan is a technology professional with over 20 years experience of working in various IT roles. He has a interest in cyber security, and has a wide range of other skills in radio, electronics and telecommunications.

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