CVE-2021-45105

Apache Log4j2 does not always protect from infinite recursion in lookup evaluation

Description

Apache Log4j2 versions 2.0-alpha1 through 2.16.0 (excluding 2.12.3 and 2.3.1) 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, 2.12.3, and 2.3.1.

Remediation

Workaround:

  • Implement one of the following mitigation techniques: * Java 8 (or later) users should upgrade to release 2.17.0. Alternatively, this can be mitigated in configuration: * In PatternLayout in the logging configuration, replace Context Lookups like `${ctx:loginId}` or `$${ctx:loginId}` with Thread Context Map patterns (%X, %mdc, or %MDC). * Otherwise, in the configuration, remove references to Context Lookups like `${ctx:loginId}` or `$${ctx:loginId}` where they originate from sources external to the application such as HTTP headers or user input.

Category

5.9
CVSS
Severity: Medium
CVSS 3.1 •
CVSS 2.0 •
EPSS 72.18% Top 5%
Vendor Advisory cisco.com Vendor Advisory debian.org Vendor Advisory apache.org
Affected: Apache Software Foundation Apache Log4j2
Published at:
Updated at:

References

Link Tags
https://logging.apache.org/log4j/2.x/security.html release notes vendor advisory
https://psirt.global.sonicwall.com/vuln-detail/SNWLID-2021-0032 third party advisory
https://www.kb.cert.org/vuls/id/930724 third party advisory us government resource
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-apache-log4j-qRuKNEbd third party advisory vendor advisory
http://www.openwall.com/lists/oss-security/2021/12/19/1 mailing list third party advisory mitigation
https://www.debian.org/security/2021/dsa-5024 third party advisory vendor advisory
https://cert-portal.siemens.com/productcert/pdf/ssa-479842.pdf third party advisory
https://security.netapp.com/advisory/ntap-20211218-0001/ third party advisory
https://www.zerodayinitiative.com/advisories/ZDI-21-1541/ vdb entry third party advisory
https://cert-portal.siemens.com/productcert/pdf/ssa-501673.pdf third party advisory
https://www.oracle.com/security-alerts/cpujan2022.html third party advisory patch
https://www.oracle.com/security-alerts/cpuapr2022.html third party advisory patch
https://www.oracle.com/security-alerts/cpujul2022.html third party advisory

Frequently Asked Questions

What is the severity of CVE-2021-45105?
CVE-2021-45105 has been scored as a medium severity vulnerability.
How to fix CVE-2021-45105?
As a workaround for remediating CVE-2021-45105: Implement one of the following mitigation techniques: * Java 8 (or later) users should upgrade to release 2.17.0. Alternatively, this can be mitigated in configuration: * In PatternLayout in the logging configuration, replace Context Lookups like `${ctx:loginId}` or `$${ctx:loginId}` with Thread Context Map patterns (%X, %mdc, or %MDC). * Otherwise, in the configuration, remove references to Context Lookups like `${ctx:loginId}` or `$${ctx:loginId}` where they originate from sources external to the application such as HTTP headers or user input.
Is CVE-2021-45105 being actively exploited in the wild?
It is possible that CVE-2021-45105 is being exploited or will be exploited in a near future based on public information. According to its EPSS score, there is a ~72% probability that this vulnerability will be exploited by malicious actors in the next 30 days.
What software or system is affected by CVE-2021-45105?
CVE-2021-45105 affects Apache Software Foundation Apache Log4j2.
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