Outline for November 3, 2025

Reading: text, §18.2, 24.3–24.4
Assignments: Homework 3, due November 5; Project selection, due November 7

1. Greetings and Felicitations!

2. Example flaws
   1. fingerd buffer overflow
   2. xterm race condition

3. RISOS
   1. Goal: Aid managers, others in understanding security issues in OSes, and work required to make them more secure
   2. Incomplete parameter validation — failing to check that a parameter used as an array index is in the range of the array;
   3. Inconsistent parameter validation — if a routine allowing shared access to files accepts blanks in a file name, but no other file manipulation routine (such as a routine to revoke shared access) will accept them;
   4. Implicit sharing of privileged/confidential data — sending information by modulating the load average of the system;
   5. Asynchronous validation/Inadequate serialization — checking a file for access permission and opening it non-atomically, thereby allowing another process to change the binding of the name to the data between the check and the open;
   6. Inadequate identification/authentication/authorization — running a system program identified only by name, and having a different program with the same name executed;
   7. Violable prohibition/limit — being able to manipulate data outside one’s protection domain; and
   8. Exploitable logic error — preventing a program from opening a critical file, causing the program to execute an error routine that gives the user unauthorized rights.

4. PA Model (Neumann’s organization)
   1. Goal: develop techniques to search for vulnerabilities that less experienced people could use
   2. Improper protection (initialization and enforcement)
      1. Improper choice of initial protection domain — incorrect initial assignment of security or integrity level at system initialization or generation; a security critical function manipulating critical data directly accessible to the user;
      2. Improper isolation of implementation detail — allowing users to bypass operating system controls and write to absolute input/output addresses; direct manipulation of a hidden data structure such as a directory file being written to as if it were a regular file; drawing inferences from paging activity
      3. Improper change — the time-of-check to time-of-use flaw; changing a parameter unexpectedly;
      4. Improper naming — allowing two different objects to have the same name, resulting in confusion over which is referenced;
      5. Improper deallocation or deletion — leaving old data in memory deallocated by one process and reallocated to another process, enabling the second process to access the information used by the first; failing to end a session properly
   3. Improper validation — not checking critical conditions and parameters, so a process addresses memory not in its memory space by referencing through an out-of-bounds pointer value; allowing type clashes; overflows
   4. Improper synchronization
      1. Improper indivisibility — interrupting atomic operations (e.g. locking); cache inconsistency
      2. Improper sequencing — allowing actions in an incorrect order (e.g. reading during writing)
   5. Improper choice of operand or operation — using unfair scheduling algorithms that block certain processes or users from running; using the wrong function or wrong arguments.

5. NRL
   1. Goal: Find out how vulnerabilities enter the system, when they enter the system, and where they are
   2. Axis 1: inadvertent (RISOS classes) vs. intentional (malicious/nonmalicious)
   3. Axis 2: time of introduction (development, maintenance, operation)
   4. Axis 3: location (hardware, software: OS, support utilities, applications)

6. Aslam
   1. Goal: Treat vulnerabilities as faults
   2. Coding faults — introduced during software development
      1. Synchronization errors
      2. Validation errors
   3. Emergent faults — introduced by incorrect initialization, use, or application
      1. Configuration errors
      2. Environment faults
   4. Introduced decision procedure to classify vulnerabilities in exactly one category

Matt Bishop Office: 2209 Watershed Sciences Phone: +1 (530) 752-8060 Email: mabishop@ucdavis.edu

ECS 235A, Computer and Information Security Version of October 31, 2025 at 2:47PM

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