Is the log4j vulnerability issue affect springboot 1.5.6 starter logging?

No, spring-boot is not affected "per se", neither springboot-starter-logging: 1.5.6.

• Proof#1: https://spring.io/blog/2021/12/10/log4j2-vulnerability-and-spring-boot

• Proof#2:

>mvn dependency:tree

---------------------< com.example:mavenproject1 >----------------------
Building mavenproject1 1.0.0-SNAPSHOT
--------------------------------[ jar ]---------------------------------

--- maven-dependency-plugin:2.10:tree (default-cli) @ mavenproject1 ---
com.example:mavenproject1:jar:1.0.0-SNAPSHOT
+- org.springframework.boot:spring-boot-starter-logging:jar:1.5.6.RELEASE:compile
|  +- ch.qos.logback:logback-classic:jar:1.1.11:compile
|  |  +- ch.qos.logback:logback-core:jar:1.1.11:compile
|  |  \- org.slf4j:slf4j-api:jar:1.7.25:compile
|  +- org.slf4j:jcl-over-slf4j:jar:1.7.25:compile
|  +- org.slf4j:jul-to-slf4j:jar:1.7.25:compile
|  \- org.slf4j:log4j-over-slf4j:jar:1.7.25:compile
+- junit:junit:jar:4.12:test
|  \- org.hamcrest:hamcrest-core:jar:1.3:test
+- org.assertj:assertj-core:jar:2.6.0:test
+- org.mockito:mockito-core:jar:1.10.19:test
|  \- org.objenesis:objenesis:jar:2.1:test
+- org.hamcrest:hamcrest-library:jar:1.3:test
\- org.springframework:spring-test:jar:4.3.10.RELEASE:test
   \- org.springframework:spring-core:jar:4.3.10.RELEASE:test
------------------------------------------------------------------------
BUILD SUCCESS
------------------------------------------------------------------------
Total time:  1.179 s
Finished at: 2022-01-08T08:32:43+01:00
------------------------------------------------------------------------

We have/had/will become a problem, when we have:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-log4j2</artifactId>
</dependency>