How severe is CVE-2021-45105?

CVE-2021-45105 has a CVSS score of 5.9/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2021-45105?

CVE-2021-45105 affects the following packages: org.apache.logging.log4j:log4j-core (Maven), org.apache.logging.log4j:log4j-core (Maven), org.apache.logging.log4j:log4j-core (Maven), org.ops4j.pax.logging:pax-logging-log4j2 (Maven), org.ops4j.pax.logging:pax-logging-log4j2 (Maven), org.ops4j.pax.logging:pax-logging-log4j2 (Maven), org.ops4j.pax.logging:pax-logging-log4j2 (Maven). Ecosystems affected: Maven.

How do I fix CVE-2021-45105?

Update org.apache.logging.log4j:log4j-core to 2.12.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-45105 is resolved across your whole dependency graph.

How do I detect CVE-2021-45105 in my Maven dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.apache.logging.log4j:log4j-core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2021-45105 if there is no patch (or I can't update yet)?

Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Is CVE-2021-45105 actively exploited in the wild?

Yes. There are 4 known exploit references for CVE-2021-45105, including 2 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-2021-45105?

CVE-2021-45105 has an EPSS (Exploit Prediction Scoring System) score of 100.0%, placing it in the 100th 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. A score above 50% indicates significantly elevated exploitation risk — immediate patching is strongly recommended.

What type of vulnerability is CVE-2021-45105?

CVE-2021-45105 is classified as Improper Input Validation (CWE-20), CWE-674 (CWE-674). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2021-45105 published, and has it been updated?

CVE-2021-45105 was published on December 18, 2021 and was last updated on October 20, 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-2021-45105 — log4j-core

MEDIUM

CVE-2021-45105 is a medium-severity (CVSS 5.9) Improper Input Validation vulnerability in org.apache.logging.log4j:log4j-core. 4 public exploit references exist, so weaponization risk is real. A fix is available for org.apache.logging.log4j:log4j-core — see the affected versions and patch details below.

Apache Log4j2 vulnerable to Improper Input Validation and Uncontrolled Recursion

Also known asGHSA-p6xc-xr62-6r2g

Published

Dec 18, 2021

Updated

Oct 20, 2026

Affected

7 pkgs

Patched

7 / 7

Exploits

4 known

Exploitation data as of Oct 21, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2021-45105.

EPSS Exploitation Probability

via FIRST.org ↗

100.0%probability of exploitation in next 30 days

Very High Risk0.00%

Lower risk than most CVEs100th percentile — riskier than 100% of all scored CVEsHighest risk

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

How urgent is this, really

CVE-2021-45105 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 394,415 CVEs with a current EPSS score, this one falls in the ≥ 90% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

7 pkgs affected

☕org.apache.logging.log4j:log4j-core☕org.apache.logging.log4j:log4j-core☕org.apache.logging.log4j:log4j-core☕org.ops4j.pax.logging:pax-logging-log4j2☕org.ops4j.pax.logging:pax-logging-log4j2☕org.ops4j.pax.logging:pax-logging-log4j2☕org.ops4j.pax.logging:pax-logging-log4j2

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

Affected packages

Only the org.apache.logging.log4j:log4j-core package is directly affected by this vulnerability. The org.apache.logging.log4j:log4j-api should be kept at the same version as the org.apache.logging.log4j:log4j-core package to ensure compatability if in use.

Affected Packages

7 total 7 fixed

Ecosystem	Package	Vulnerable range	Fix
☕Maven	`org.apache.logging.log4j:log4j-core`	≥ 2.4.0&&< 2.12.3	2.12.3`org.apache.logging.log4j:log4j-core:2.12.3`
☕Maven	`org.apache.logging.log4j:log4j-core`	≥ 2.13.0&&< 2.17.0	2.17.0`org.apache.logging.log4j:log4j-core:2.17.0`
☕Maven	`org.apache.logging.log4j:log4j-core`	all versions	2.3.1`org.apache.logging.log4j:log4j-core:2.3.1`
☕Maven	`org.ops4j.pax.logging:pax-logging-log4j2`	≥ 1.8.0&&< 1.9.2	1.9.2`org.ops4j.pax.logging:pax-logging-log4j2:1.9.2`
☕Maven	`org.ops4j.pax.logging:pax-logging-log4j2`	≥ 1.10.0&&< 1.10.9	1.10.9`org.ops4j.pax.logging:pax-logging-log4j2:1.10.9`
☕Maven	`org.ops4j.pax.logging:pax-logging-log4j2`	≥ 1.11.0&&< 1.11.12	1.11.12`org.ops4j.pax.logging:pax-logging-log4j2:1.11.12`

Affected Products

116 products · 208 configurations

Application

log4japache

≥ 2.13.0 && ≤ 2.16.0

range

debian linuxdebian

2 versions

10.011.0

Application

cloud managernetapp

all

Application

agile engineering data managementoracle

1 version

6.2.1.0

Application

agile plm mcad connectororacle

1 version

3.6

Application

agile product lifecycle managementoracle

1 version

9.3.6

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.

Apache Log4j2 versions 2.0-alpha1 through 2.16.0 (excluding 2.12.3 and 2…

github.comGithubDec 2021

Apache Log4j2 versions 2.0-alpha1 through 2.16.0 (excluding 2.12.3 and 2…

github.comGithubDec 2021

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.apache.logging.log4j:log4j-core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update org.apache.logging.log4j:log4j-core to 2.12.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-45105 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

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 Product Security has performed an analysis of this flaw and has classified the Attack Complexity(AC) as High because there are multiple factors involved which are beyond attacker's control: - The application has to use the logging configuration using a Context Map Lookup (for example, $${ctx:loginId}) which is…

Workaround published by Red Hat

For Log4j 2 versions up to and including 2.16.0, this flaw can be mitigated by: - In PatternLayout in the Log4j logging configuration, replace Context Lookups like ${ctx:loginId} or $${ctx:loginId} with Thread Context Map patterns (%X, %mdc, or %MDC) like %X{loginId}. - Otherwise, in the Log4j logging configuration, remove references to Context Lookups like ${ctx:loginId} or $${ctx:loginId} where they originate from sources external to the application such as HTTP headers or user input.

Source: Red Hat security advisory for CVE-2021-45105 (CC BY 4.0)

Product	Fixed in	Advisory
OpenShift Logging 5.0	`openshift-logging/elasticsearch6-rhel8:v5.0.11-2`	RHSA-2022:0047
OpenShift Logging 5.1	`openshift-logging/elasticsearch6-rhel8:v6.8.1-82`	RHSA-2022:0042
OpenShift Logging 5.2	`openshift-logging/elasticsearch6-rhel8:v6.8.1-83`	RHSA-2022:0043
OpenShift Logging 5.3	`openshift-logging/elasticsearch6-rhel8:v6.8.1-84`	RHSA-2022:0044
Red Hat AMQ Streams 1.6.6	see advisory	RHSA-2022:0219
Red Hat Data Grid 8.2.3	`log4j-core`	RHSA-2022:0205
Red Hat Fuse 7.8.2, 7.9.1, 7.10.1	`log4j-core`	RHSA-2022:0203
Red Hat Integration Camel Extensions for Quarkus 2.2	see advisory	RHSA-2022:0222

UbuntuMEDIUM

USN-5203-1Ubuntu USN-5222-1Ubuntu

Frequently Asked Questions

Apache Log4j2 versions 2.0-alpha1 through 2.16.0 (excluding 2.12.3) did not protect from uncontrolled recursion from self-referential lookups. This allows an attacker with control over Thread Context Map data to cause a denial of service when a crafted string is interpreted. This issue was fixed in Log4j 2.17.0 and 2.12.3. # Affected packages Only the `org.apache.logging.log4j:log4j-core` package is directly affected by this vulnerability. The `org.apache.logging.log4j:log4j-api` should be kept at the same version as the `org.apache.logging.log4j:log4j-core` package to ensure compatability i

O3 Security · Impact-Aware SCA

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Find it across Maven, including transitive dependencies.

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CVSS Score

5.9/10CVSS v3 base

Vector breakdown

Attack Vector

Network

Attack Complexity

High

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

Raw vector

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

CWE Classification

CWE-20Improper Input Validation CWE-674CWE-674

Weaponization

No known public exploit tooling found.

Timeline

Disclosed

Dec 18, 2021

First exploit

Dec 18, 2021

Same day as disclosure — rapid exploitation

Last updated

Oct 20, 2026

Identifiers

CVE-2021-45105

GHSA-p6xc-xr62-6r2g

Related vulnerabilities

This CVE is medium severity; 8 of 8 other CVEs affecting log4j-core are rated as high or higher (top: critical).

CVE-2026-34480CVE-2026-34478CVE-2026-34477CVE-2025-68161CVE-2023-26464CVE-2021-44832CVE-2021-45046CVE-2021-44228

Provenance

Sources

OSV.devNVDFIRST.org (EPSS)

Last verifiedOct 20, 2026

CVE-2021-45105 — log4j-core

Exploitation Status

No confirmed exploitation observed yet

EPSS Exploitation Probability

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

Description

Affected packages

Affected Packages

Affected Products

Detection & mitigation playbook

Detect

Fix

Workarounds

Fixing This On Your OS

Frequently Asked Questions

Is CVE-2021-45105 in your dependencies?