cURL and libcurl verify_certificate Function Out-of-Bounds Read Vulnerability [CVE-2016-9953]

CVE Number – CVE-2016-9953

A vulnerability in cURL and libcurl could allow an unauthenticated, remote attacker to completely compromise 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 trigger an out-of-bounds read condition, resulting in a complete system compromise.The cURL Project has confirmed the vulnerability and released software updates.


  • To exploit this vulnerability, the attacker must supply a server certificate that contains a malicious wildcard SAN to the targeted system, making exploitation more difficult in environments that restrict network access from untrusted sources.


  • 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-2016-9953

Fixed Software

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

Duncan Newell

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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