A security vulnerability has been identified in all supported versions of OpenSSL related to the verification of X.509 certificate chains that include policy constraints. Attackers may be able to exploit this vulnerability by creating a malicious certificate chain that triggers exponential use of computational resources, leading to a denial-of-service (DoS) attack on affected systems.

Policy processing is disabled by default but can be enabled by passing the -policy argument to the command line utilities or by calling the X509_VERIFY_PARAM_set1_policies() function.

Applications that use a non-default option when verifying certificates may be vulnerable to an attack from a malicious CA to circumvent certain checks.

Invalid certificate policies in leaf certificates are silently ignored by OpenSSL and other certificate policy checks are skipped for that certificate. A malicious CA could use this to deliberately assert invalid certificate policies in order to circumvent policy checking on the certificate altogether.

Policy processing is disabled by default but can be enabled by passing the -policy argument to the command line utilities or by calling the X509_VERIFY_PARAM_set1_policies() function.

The function X509_VERIFY_PARAM_add0_policy() is documented to implicitly enable the certificate policy check when doing certificate verification. However the implementation of the function does not enable the check which allows certificates with invalid or incorrect policies to pass the certificate verification.

As suddenly enabling the policy check could break existing deployments it was decided to keep the existing behavior of the X509_VERIFY_PARAM_add0_policy() function.

Instead the applications that require OpenSSL to perform certificate policy check need to use X509_VERIFY_PARAM_set1_policies() or explicitly enable the policy check by calling X509_VERIFY_PARAM_set_flags() with the X509_V_FLAG_POLICY_CHECK flag argument.

Certificate policy checks are disabled by default in OpenSSL and are not commonly used by applications.

The webserver implementation of the affected products does not correctly release allocated memory after it has been used.

An attacker with network access could use this vulnerability to cause a denial-of-service condition in the webserver of the affected product.

The web server of affected products, if configured to allow the import of PKCS12 containers, could end up in an infinite loop when processing incomplete certificate chains.

This could allow an authenticated remote attacker to create a denial of service condition by importing specially crafted PKCS12 containers.