How severe is CVE-2021-42550?

CVE-2021-42550 has a CVSS score of 6.6/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2021-42550?

CVE-2021-42550 affects the following packages: ch.qos.logback:logback-core (Maven). Ecosystems affected: Maven.

How do I fix CVE-2021-42550?

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.

How do I detect CVE-2021-42550 in my Maven dependencies?

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.

How do I mitigate CVE-2021-42550 if there is no patch (or I can't update yet)?

Do not deserialise data from untrusted sources: where the format allows it, restrict deserialisation to an explicit allowlist of expected types, and prefer a data-only format (JSON, Protobuf) over one that can reconstruct arbitrary objects until you can upgrade.

Is CVE-2021-42550 actively exploited in the wild?

Yes. There are 3 known exploit references for CVE-2021-42550, including 3 in-the-wild exploitations observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-42550?

CVE-2021-42550 has an EPSS (Exploit Prediction Scoring System) score of 4.8%, placing it in the 92th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2021-42550?

CVE-2021-42550 is classified as Deserialization of Untrusted Data (CWE-502). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

When was CVE-2021-42550 published, and has it been updated?

CVE-2021-42550 was published on December 16, 2021 and was last updated on October 24, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

☕

☕ Maven

Not in CISA KEV

MEDIUM severity

CVE-2021-42550 — logback-core

MEDIUMFix: qos-ch/logback@8729107

CVE-2021-42550 is a medium-severity (CVSS 6.6) Deserialization of Untrusted Data vulnerability in ch.qos.logback:logback-core. 3 public exploit or proof-of-concept references are indexed, 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

Also known asGHSA-668q-qrv7-99fm

Published

Dec 16, 2021

Updated

Oct 24, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

3 known

Exploitation data as of Nov 2, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

4.8%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs92th percentile — riskier than 92% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected

☕ch.qos.logback:logback-core

Real-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

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
☕Maven	`ch.qos.logback:logback-core`	all versions	1.2.9`ch.qos.logback:logback-core:1.2.9`

Affected Products

6 products · 17 configurations

Application

cloud managernetapp

all

Application

service level managernetapp

all

Application

snap creator frameworknetapp

all

Application

logbackqos

≤ 1.2.7

1 version

1.3.0

Application

satelliteredhat

1 version

6.0

Application

sinec nmssiemens

< 1.0.3

range

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

In logback version 1.2.7 and prior versions, an attacker with the requir…

github.comNVDDec 2021

Report on jira.qos.ch

jira.qos.chNVDDec 2021

Report on packetstormsecurity.com

packetstormsecurity.comNVDOct 2022

Detection & mitigation playbook

Open-source dependency

Detect
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
Do not deserialise data from untrusted sources: where the format allows it, restrict deserialisation to an explicit allowlist of expected types, and prefer a data-only format (JSON, Protobuf) over one that can reconstruct arbitrary objects until you can upgrade.

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 HatModerate

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

O3 Security · Impact-Aware SCA

Is CVE-2021-42550 in your dependencies?

Find it across Maven, including transitive dependencies.

Scan my dependencies How O3 SCA works

CVE-2021-42550 — logback-core

EPSS Exploitation Probability

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

Description

Affected Packages

Affected Products

Detection & mitigation playbook

Detect

Fix

Workarounds

Fixing This On Your OS

Frequently Asked Questions

Is CVE-2021-42550 in your dependencies?