Inefficient regular expression (js/redos)

[alensiljak]

A security code scanner reports the following issue in the moxie.js v1.5.8 code:

Finding details
Tool
CodeQL
Rule ID
js/redos
Weaknesses
CWE-1333
CWE-730
CWE-400

Description

Some regular expressions take a long time to match certain input strings to the point where the time it takes to match a string of length n is proportional to nk or even 2n. Such regular expressions can negatively affect performance, or even allow a malicious user to perform a Denial of Service ("DoS") attack by crafting an expensive input string for the regular expression to match.

The regular expression engines provided by many popular JavaScript platforms use backtracking non-deterministic finite automata to implement regular expression matching. While this approach is space-efficient and allows supporting advanced features like capture groups, it is not time-efficient in general. The worst-case time complexity of such an automaton can be polynomial or even exponential, meaning that for strings of a certain shape, increasing the input length by ten characters may make the automaton about 1000 times slower.

Typically, a regular expression is affected by this problem if it contains a repetition of the form r* or r+ where the sub-expression r is ambiguous in the sense that it can match some string in multiple ways. More information about the precise circumstances can be found in the references.

Recommendation

Modify the regular expression to remove the ambiguity, or ensure that the strings matched with the regular expression are short enough that the time-complexity does not matter.