Apache Log4j2 vulnerable to Improper Input Validation and Uncontrolled Recursion

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

8.6 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H

EPSS

• CVE-2021-45105: 100.00% estimated exploitation activity in the next 30 days; percentile 99.99 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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 if in use.

Published by the source

18 Dec 2021, 18:00 UTC

Last modified by the source

9 Jun 2026, 10:26 UTC

Source last checked

26 Oct 2026, 16:45 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-p6xc-xr62-6r2g

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# Patch Next advisory brief: CVE-2021-45105

Advisory: Apache Log4j2 vulnerable to Improper Input Validation and Uncontrolled Recursion
IDs: CVE-2021-45105, GHSA-p6xc-xr62-6r2g
Record: https://patchnext.com/advisories/cve-2021-45105 (revision 1, source checked 26 Oct 2026, 16:45 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.6)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: org.ops4j.pax.logging:pax-logging-log4j2 2.0.13, 1.11.12, 1.10.9, 1.9.2; org.apache.logging.log4j:log4j-core 2.17.0, 2.12.3, 2.3.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven org.ops4j.pax.logging:pax-logging-log4j2: affected >= 1.8.0, < 1.9.2; >= 1.10.0, < 1.10.9; >= 1.11.0, < 1.11.12; >= 2.0.0, < 2.0.13; fixed in 2.0.13, 1.9.2, 1.10.9, 1.11.12
- Maven org.apache.logging.log4j:log4j-core: affected >= 2.4.0, < 2.12.3; >= 2.13.0, < 2.17.0; < 2.3.1; fixed in 2.17.0, 2.12.3, 2.3.1

## Suggested inspection (read-only)
- Maven org.ops4j.pax.logging:pax-logging-log4j2: check the installed version with your package manager.
- Maven org.apache.logging.log4j:log4j-core: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on org.ops4j.pax.logging:pax-logging-log4j2, org.apache.logging.log4j:log4j-core.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-p6xc-xr62-6r2g (GitHub-reviewed advisory GHSA-p6xc-xr62-6r2g lists affected ranges: Maven org.apache.logging.log4j:log4j-core >=2.4.0 =2.13.0 =0 =1.8.0 =1.10.0 =1.11.0 =2.0.0 <2.0.13)

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