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:cve-url-prefix: https://nvd.nist.gov/vuln/detail

= Security

The Apache Log4j Security Team takes security seriously.
This allows our users to place their trust in Log4j for protecting their mission-critical data.
In this page we will help you find guidance on security-related issues and access to known vulnerabilities.

include::_log4j1-eol.adoc[]

[#support]
== Getting support

If you need help on building or configuring Log4j or other help on following the instructions to mitigate the known vulnerabilities listed here, please use our xref:support.adoc#discussions[user support channels].

[TIP]
====
If you need to apply a source code patch, use the building instructions for the Log4j version that you are using.
These instructions can be found in `BUILDING.adoc` distributed with the sources.
====

[#reporting]
== Reporting vulnerabilities

If you have encountered an unlisted security vulnerability or other unexpected behaviour that has a security impact, or if the descriptions here are incomplete, please report them **privately** to mailto:security@logging.apache.org[the Log4j Security Team].

[WARNING]
====
The threat model that Log4j uses considers configuration files as safe input controlled by the programmer; **potential vulnerabilities that require the ability to modify a configuration are not considered vulnerabilities** as the required access to do so implies the attacker can execute arbitrary code.
====

[#policy]
== Vulnerability handling policy

The Apache Log4j Security Team follows the https://www.apache.org/security/committers.html[ASF Project Security] guide for handling security vulnerabilities.

Reported security vulnerabilities are subject to voting (by means of https://logging.apache.org/guidelines.html[_lazy approval_], preferably) in the private mailto:security@logging.apache.org[security mailing list] before creating a CVE and populating its associated content.
This procedure involves only the creation of CVEs and blocks neither (vulnerability) fixes, nor releases.

[#vdr]
== Vulnerability Disclosure Report (VDR)

Starting with version `2.22.0`, Log4j distributes https://cyclonedx.org/capabilities/vdr[CycloneDX Software Bill of Materials (SBOM)] along with each deployed artifact.
Produced SBOMs contain BOM-links referring to a https://cyclonedx.org/capabilities/vdr[CycloneDX Vulnerability Disclosure Report (VDR)] that Apache Logging Services uses for all projects it maintains.
All this is streamlined by `logging-parent`, see https://logging.apache.org/logging-parent/latest/#cyclonedx-sbom[its website] for details.

[#vulnerabilities]
== Known vulnerabilities

The Log4j Security Team believes that accuracy, completeness and availability of security information is essential for our users.
We choose to pool all information on this one page, allowing easy searching for security vulnerabilities over a range of criteria.

[NOTE]
====
We adhere to https://maven.apache.org/enforcer/enforcer-rules/versionRanges.html[the Maven version range syntax] while sharing versions of affected components.
We only extend this mathematical notation with set union operator (i.e., `∪`) to denote union of multiple ranges.
====

[#CVE-2021-44832]
=== {cve-url-prefix}/CVE-2021-44832[CVE-2021-44832]

[cols="1h,5"]
|===
|Summary |JDBC appender is vulnerable to remote code execution in certain configurations
|CVSS 3.x Score & Vector |6.6 MEDIUM (CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H)
|Components affected |`log4j-core`
|Versions affected |`[2.0-beta7, 2.3.2) ∪ [2.4, 2.12.4) ∪ [2.13.0, 2.17.1)`
|Versions fixed |`2.3.2` (for Java 6), `2.12.4` (for Java 7), or `2.17.1` (for Java 8 and later)
|===

[#CVE-2021-44832-description]
==== Description

An attacker with write access to the logging configuration can construct a malicious configuration using a JDBC Appender with a data source referencing a JNDI URI which can execute remote code.
This issue is fixed by limiting JNDI data source names to the `java` protocol.

[#CVE-2021-44832-mitigation]
==== Mitigation

Upgrade to `2.3.2` (for Java 6), `2.12.4` (for Java 7), or `2.17.1` (for Java 8 and later).

In prior releases confirm that if the JDBC Appender is being used it is not configured to use any protocol other than `java`.

[#CVE-2021-44832-references]
==== References
- {cve-url-prefix}/CVE-2021-44832[CVE-2021-44832]

[#CVE-2021-45105]
=== {cve-url-prefix}/CVE-2021-45105[CVE-2021-45105]

[cols="1h,5"]
|===
|Summary |Infinite recursion in lookup evaluation
|CVSS 3.x Score & Vector |5.9 MEDIUM (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H)
|Components affected |`log4j-core`
|Versions affected |`[2.0-alpha1, 2.3.1) ∪ [2.4, 2.12.3) ∪ [2.13.0, 2.17.0)`
|Versions fixed |`2.3.1` (for Java 6), `2.12.3` (for Java 7), and `2.17.0` (for Java 8 and later)
|===

[#CVE-2021-45105-description]
==== Description

Log4j versions `2.0-alpha1` through `2.16.0` (excluding `2.3.1` and `2.12.3`), did not protect from uncontrolled recursion that can be implemented using self-referential lookups.
When the logging configuration uses a non-default Pattern Layout with a Context Lookup (for example, `$${ctx:loginId}`), attackers with control over Thread Context Map (MDC) input data can craft malicious input data that contains a recursive lookup, resulting in a `StackOverflowError` that will terminate the process.
This is also known as a _DoS (Denial-of-Service)_ attack.

[#CVE-2021-45105-mitigation]
==== Mitigation

Upgrade to `2.3.1` (for Java 6), `2.12.3` (for Java 7), or `2.17.0` (for Java 8 and later).

Alternatively, this infinite recursion issue 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.
Note that this mitigation is insufficient in releases older than `2.12.2` (for Java 7), and `2.16.0` (for Java 8 and later) as the issues fixed in those releases will still be present.

Note that only the `log4j-core` JAR file is impacted by this vulnerability.
Applications using only the `log4j-api` JAR file without the `log4j-core` JAR file are not impacted by this vulnerability.

[#CVE-2021-45105-credits]
==== Credits

Independently discovered by Hideki Okamoto of Akamai Technologies, Guy Lederfein of Trend Micro Research working with Trend Micro's Zero Day Initiative, and another anonymous vulnerability researcher.

[#CVE-2021-45105-references]
==== References

- {cve-url-prefix}/CVE-2021-45105[CVE-2021-45105]
- https://issues.apache.org/jira/browse/LOG4J2-3230[LOG4J2-3230]

[#CVE-2021-45046]
=== {cve-url-prefix}/CVE-2021-45046[CVE-2021-45046]

[cols="1h,5"]
|===
|Summary |Thread Context Lookup is vulnerable to remote code execution in certain configurations
|CVSS 3.x Score & Vector |9.0 CRITICAL (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H)
|Components affected |`log4j-core`
|Versions affected |`[2.0-beta9, 2.3.1) ∪ [2.4, 2.12.3) ∪ [2.13.0, 2.17.0)`
|Versions fixed |`2.3.1` (for Java 6), `2.12.3` (for Java 7), and `2.17.0` (for Java 8 and later)
|===

[#CVE-2021-45046-description]
==== Description

It was found that the fix to address <<CVE-2021-44228>> in Log4j `2.15.0` was incomplete in certain non-default configurations.
When the logging configuration uses a non-default Pattern Layout with a Thread Context Lookup (for example, `$${ctx:loginId}`), attackers with control over Thread Context Map (MDC) can craft malicious input data using a JNDI Lookup pattern, resulting in an information leak and remote code execution in some environments and local code execution in all environments.
Remote code execution has been demonstrated on macOS, Fedora, Arch Linux, and Alpine Linux.

Note that this vulnerability is not limited to just the JNDI lookup.
Any other Lookup could also be included in a Thread Context Map variable and possibly have private details exposed to anyone with access to the logs.

Note that only the `log4j-core` JAR file is impacted by this vulnerability.
Applications using only the `log4j-api` JAR file without the `log4j-core` JAR file are not impacted by this vulnerability.

[#CVE-2021-45046-mitigation]
==== Mitigation

Upgrade to Log4j `2.3.1` (for Java 6), `2.12.3` (for Java 7), or `2.17.0` (for Java 8 and later).

[#CVE-2021-45046-credits]
==== Credits

This issue was discovered by Kai Mindermann of iC Consult and separately by 4ra1n.

Additional vulnerability details discovered independently by Ash Fox of Google, Alvaro Muñoz and Tony Torralba from GitHub, Anthony Weems of Praetorian, and RyotaK (@ryotkak).

[#CVE-2021-45046-references]
==== References

- {cve-url-prefix}/CVE-2021-45046[CVE-2021-45046]
- https://issues.apache.org/jira/browse/LOG4J2-3221[LOG4J2-3221]

[#CVE-2021-44228]
=== {cve-url-prefix}/CVE-2021-44228[CVE-2021-44228]

[cols="1h,5"]
|===
|Summary |JNDI lookup can be exploited to execute arbitrary code loaded from an LDAP server
|CVSS 3.x Score & Vector |10.0 CRITICAL (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H)
|Components affected |`log4j-core`
|Versions affected |`[2.0-beta9, 2.3.1) ∪ [2.4, 2.12.3) ∪ [2.13.0, 2.17.0)`
|Versions fixed |`2.3.1` (for Java 6), `2.12.3` (for Java 7), and `2.17.0` (for Java 8 and later)
|===

[#CVE-2021-44228-description]
==== Description

In Log4j, the JNDI features used in configurations, log messages, and parameters do not protect against attacker-controlled LDAP and other JNDI related endpoints.
An attacker who can control log messages or log message parameters can execute arbitrary code loaded from LDAP servers.

Note that only the `log4j-core` JAR file is impacted by this vulnerability.
Applications using only the `log4j-api` JAR file without the `log4j-core` JAR file are not impacted by this vulnerability.

[#CVE-2021-44228-mitigation]
==== Mitigation

[#CVE-2021-44228-mitigation-log4j1]
===== Log4j 1 mitigation

include::_log4j1-eol.adoc[]

Log4j 1 does not have Lookups, so the risk is lower.
Applications using Log4j 1 are only vulnerable to this attack when they use JNDI in their configuration.
A separate CVE ({cve-url-prefix}/CVE-2021-4104[CVE-2021-4104]) has been filed for this vulnerability.
To mitigate, audit your logging configuration to ensure it has no `JMSAppender` configured.
Log4j 1 configurations without `JMSAppender` are not impacted by this vulnerability.

[#CVE-2021-44228-mitigation-log4j2]
===== Log4j 2 mitigation

Upgrade to Log4j `2.3.1` (for Java 6), `2.12.3` (for Java 7), or `2.17.0` (for Java 8 and later).

[#CVE-2021-44228-credits]
==== Credits

This issue was discovered by Chen Zhaojun of Alibaba Cloud Security Team.

[#CVE-2021-44228-references]
==== References

- {cve-url-prefix}/CVE-2021-44228[CVE-2021-44228]
- https://issues.apache.org/jira/browse/LOG4J2-3198[LOG4J2-3198]
- https://issues.apache.org/jira/browse/LOG4J2-3201[LOG4J2-3201]

[#CVE-2020-9488]
=== {cve-url-prefix}/CVE-2020-9488[CVE-2020-9488]

[cols="1h,5"]
|===
|Summary |Improper validation of certificate with host mismatch in SMTP appender
|CVSS 3.x Score & Vector |3.7 LOW (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N)
|Components affected |`log4j-core`
|Versions affected |`[2.0-beta1, 2.12.3) ∪ [2.13.1, 2.13.2)`
|Versions fixed |`2.12.3` (Java 7) and `2.13.2` (Java 8 and later)
|===

[#CVE-2020-9488-description]
==== Description

Improper validation of certificate with host mismatch in SMTP appender.
This could allow an SMTPS connection to be intercepted by a man-in-the-middle attack which could leak any log
messages sent through that appender.

The reported issue was caused by an error in `SslConfiguration`.
Any element using `SslConfiguration` in the Log4j `Configuration` is also affected by this issue.
This includes `HttpAppender`, `SocketAppender`, and `SyslogAppender`.
Usages of `SslConfiguration` that are configured via system properties are not affected.

[#CVE-2020-9488-mitigation]
==== Mitigation

Upgrade to `2.12.3` (Java 7) or `2.13.2` (Java 8 and later).

Alternatively, users can set the `mail.smtp.ssl.checkserveridentity` system property to `true` to enable SMTPS hostname verification for all SMTPS mail sessions.

[#CVE-2020-9488-credits]
==== Credits

This issue was discovered by Peter Stöckli.

[#CVE-2020-9488-references]
==== References

- {cve-url-prefix}/CVE-2020-9488[CVE-2020-9488]
- https://issues.apache.org/jira/browse/LOG4J2-2819[LOG4J2-2819]

[#CVE-2017-5645]
=== {cve-url-prefix}/CVE-2017-5645[CVE-2017-5645]

[cols="1h,5"]
|===
|Summary |TCP/UDP socket servers can be exploited to execute arbitrary code
|CVSS 2.0 Score & Vector |7.5 HIGH (AV:N/AC:L/Au:N/C:P/I:P/A:P)
|Components affected |`log4j-core`
|Versions affected |`[2.0-alpha1, 2.8.2)`
|Versions fixed |`2.8.2` (Java 7)
|===

[#CVE-2017-5645-description]
==== Description

When using the TCP socket server or UDP socket server to receive serialized log events from another application, a specially crafted binary payload can be sent that, when deserialized, can execute arbitrary code.

[#CVE-2017-5645-mitigation]
==== Mitigation

Java 7 and above users should migrate to version `2.8.2` or avoid using the socket server classes.
Java 6 users should avoid using the TCP or UDP socket server classes, or they can manually backport https://github.com/apache/logging-log4j2/commit/5dcc192[the security fix commit] from `2.8.2`.

[#CVE-2017-5645-credits]
==== Credits

This issue was discovered by Marcio Almeida de Macedo of Red Team at Telstra.

[#CVE-2017-5645-references]
==== References

- {cve-url-prefix}/CVE-2017-5645[CVE-2017-5645]
- https://issues.apache.org/jira/browse/LOG4J2-1863[LOG4J2-1863]
- https://github.com/apache/logging-log4j2/commit/5dcc192[Security fix commit]
