Kaprica Security (KPRCA)
This service implements a command line evaluation engine for a programming language referred to as SLUR. The service takes in a SLUR expression and evaluates it, returning the evaluated expression back to the user. The SLUR language is based off of lists. Each expression is itself a list, expressions are written usually to modify or build lists in some interesting way. The SLUR evaluation engine we provide supports of series of primitive functions which the user can use to build their programs. In addition to functions and lists, SLUR also has the concept of atoms which are strings of characters and numbers that aren't the names of functions. Formally, a list is a parenthesis pair, enclosing zero or more atoms or lists.
The built in functions are as follow: * (quote e) returns e * (cons e1 e2) returns the list formed by prepending e1 onto e2 * (car e) returns the first element of the list e * (cdr e) returns all the elements of the list e minus the first one * (atom e) returns
t if e is an atom else returns
nil * (cond (p1 e1) ... (pn en)) returns the first e whose p is
t * (equal e1 e2) returns
t if e1 = e2 else returns
nil * ((lambda (v1 ... vn) e) e1 ... en) returns e evaluated in the environment where v1 -> e1, ... vn -> en.
Our SLUR machine also implements CAKE reduction functionality in the lambda function. If the result of our evaluated lambda is a list consisting of the atom "CAKE" repeated 4 times it appends the atom "That's a lot of CAKE!" to the list.
The first vulnerability is trigged in the CAKE reduction functionality. The reduction functionality has a flaw (eval.c:328) where it incorrectly appends to the internal list structure representing a SLUR list. It is possible for an attacker to trigger a null pointer dereference in cases where the CAKE reduction is being performed at the end of the list, i.e. where the tail of the list is NULL.
The second vulnerability is triggered the lambda functionality. When substituting symbols in the enclosing lambda, the substitution code does correctly validate that the object it is attempting to compare to the symbol it is substituting for which can result in a NULL pointer dereference due to assumptions the code makes about the state of values in the struct representing the object.
Null Pointer Dereference Type Confusion
CWE-476: Null Pointer Dereference CWE-843: Access of Resource Using Incompatible Type ('Type Confusion')
In order to trigger the vulnerability, the attacker must be able to successful build a program that triggers the CAKE reduction functionality. This requires the attacker to understand how the internal structure of the SLUR lists are used, how the lambda function evaluates its arguments, and that 4 CAKE atoms must be present for the vulnerability to the triggered.
Curated by Lunge Technology, LLC. Questions or comments? Send us email