CVE-2021-42550 — logback-core
MEDIUMCVE-2021-42550 is a medium-severity (CVSS 6.6) Deserialization of Untrusted Data vulnerability in ch.qos.logback:logback-core. 3 public exploit references exist, so weaponization risk is real. A fix is available for ch.qos.logback:logback-core — see the affected versions and patch details below.
Deserialization of Untrusted Data in logback
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2021-42550 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,333 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
ch.qos.logback:logback-coreReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.
Description
In logback version 1.2.7 and prior versions, an attacker with the required privileges to edit configurations files could craft a malicious configuration allowing to execute arbitrary code loaded from LDAP servers.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | ch.qos.logback:logback-core | all versions | 1.2.9ch.qos.logback:logback-core:1.2.9 |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for ch.qos.logback:logback-core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update ch.qos.logback:logback-core to 1.2.9 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-42550 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2021-42550 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2021-42550. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
Red Hat Satellite shipped affected versions, however, it is not vulnerable because the product doesn't meet the conditions needed to perform the attack.
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Fuse 7.11 | logback-classic | RHSA-2022:5532 |
| Red Hat Satellite 6.11 for RHEL 7 | candlepin-0:4.1.13-1.el7sat | RHSA-2022:5498 |
| RHDM 7.12.1 | logback-classic | RHSA-2022:1110 |
| RHPAM 7.12.1 | logback-classic | RHSA-2022:1108 |
Frequently Asked Questions
Is CVE-2021-42550 in your dependencies?
O3 Security finds CVE-2021-42550 across Maven dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.