| Name |
Regular Expression Exponential Blowup |
|
| Likelyhood of attack |
Typical severity |
| Medium |
High |
|
| Summary |
An adversary may execute an attack on a program that uses a poor Regular Expression(Regex) implementation by choosing input that results in an extreme situation for the Regex. A typical extreme situation operates at exponential time compared to the input size. This is due to most implementations using a Nondeterministic Finite Automaton(NFA) state machine to be built by the Regex algorithm since NFA allows backtracking and thus more complex regular expressions. |
| Prerequisites |
This type of an attack requires the ability to identify hosts running a poorly implemented Regex, and the ability to send crafted input to exploit the regular expression. |
| Solutions | Test custom written Regex with fuzzing to determine if the Regex is a poor one. Add timeouts to processes that handle the Regex logic. If an evil Regex is found rewrite it as a good Regex. |
| Related Weaknesses |
|
CWE ID
|
Description
|
| CWE-400 |
Uncontrolled Resource Consumption |
| CWE-1333 |
Inefficient Regular Expression Complexity |
|
| Related CAPECS |
|
CAPEC ID
|
Description
|
| CAPEC-130 |
An adversary causes the target to allocate excessive resources to servicing the attackers' request, thereby reducing the resources available for legitimate services and degrading or denying services. Usually, this attack focuses on memory allocation, but any finite resource on the target could be the attacked, including bandwidth, processing cycles, or other resources. This attack does not attempt to force this allocation through a large number of requests (that would be Resource Depletion through Flooding) but instead uses one or a small number of requests that are carefully formatted to force the target to allocate excessive resources to service this request(s). Often this attack takes advantage of a bug in the target to cause the target to allocate resources vastly beyond what would be needed for a normal request. |
|
| Taxonomy: OWASP Attacks |
|
Entry ID
|
Entry Name
|
| Link |
Regular expression Denial of Service - ReDoS |
|