Is Logback’s CVE‑2021‑42550 a Real Threat? How to Safely Upgrade
Logback’s CVE‑2021‑42550 affects versions below 1.2.9, allowing attackers with write access to the configuration file to execute arbitrary code via LDAP, but its severity is rated Medium; upgrading to 1.2.9 or newer, setting config files read‑only, and aligning Spring Boot versions can mitigate the risk.
Early this morning I saw a headline about a Logback issue that caught my attention.
Visiting the official Logback news page at https://logback.qos.ch/news.html reveals that versions below 1.2.9 are affected.
The vulnerability, identified as CVE‑2021‑42550, allows an attacker who can edit the Logback configuration file to craft a malicious configuration that loads arbitrary code from an LDAP server.
Although the description sounds severe, the official rating is MEDIUM . The issue differs from the Log4j2 “log4Shell” exploit because it requires the attacker to have write permission to the Logback configuration.
To mitigate the risk, the Logback team recommends setting the configuration file to read‑only and, if possible, upgrading to Logback 1.2.9 or newer.
For Spring Boot users, versions 2.6.2 and 2.5.8 already include Logback 1.2.9; earlier Spring Boot releases can be updated by adding logback.version in the properties section, as shown in the example image.
In summary, the vulnerability is not as critical as Log4j2, but upgrading and securing the configuration file are prudent steps.
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Programmer DD
A tinkering programmer and author of "Spring Cloud Microservices in Action"
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