Software Engineering Institute

Included in X.509 certificates are public keys used for digital signature verification. Choosing very large values for the public exponent and public modulus associated with an RSA public key may cause the verification of that key to require large amounts of system resources. According to NISCC:

...by choosing much larger values for [the public exponent and the public modulus], it may be possible to cause the verification process to consume large amounts of system resources and hence result in a denial-of-service condition.
This vulnerability can be triggered by sending a message signed using specially crafted RSA keys to affected products. A number of different products that verify RSA signatures may be vulnerable to this issue. Please see the Systems Affected section of this document for specific product information.

A remote, unauthenticated attacker could consume large amounts of system resources on an affected device, thereby creating a denial of service.

Upgrade or apply a patch from the vendor
Patches have been released to address this issue. See the systems affected section of this document for information about specific vendors.