CVE-2021-4104

CVE-2021-4104 is a high-severity vulnerability in Apache Log4j with a CVSS 3.x base score of 7.5. Its EPSS exploit-prediction score of 81% places it in the 100th percentile, indicating an elevated likelihood of exploitation. The underlying weakness is classified as CWE-502.

Key facts

Description

JMSAppender in Log4j 1.2 is vulnerable to deserialization of untrusted data when the attacker has write access to the Log4j configuration. The attacker can provide TopicBindingName and TopicConnectionFactoryBindingName configurations causing JMSAppender to perform JNDI requests that result in remote code execution in a similar fashion to CVE-2021-44228. Note this issue only affects Log4j 1.2 when specifically configured to use JMSAppender, which is not the default. Apache Log4j 1.2 reached end of life in August 2015. Users should upgrade to Log4j 2 as it addresses numerous other issues from the previous versions.

Frequently asked questions

What is CVE-2021-4104?
JMSAppender in Log4j 1.2 is vulnerable to deserialization of untrusted data when the attacker has write access to the Log4j configuration. The attacker can provide TopicBindingName and TopicConnectionFactoryBindingName configurations causing JMSAppender to perform JNDI requests that result in remote code execution in a similar fashion to CVE-2021-44228. Note this issue only affects Log4j 1.2 when specifically configured to use JMSAppender, which is not the default. Apache Log4j 1.2 reached end of life in August 2015. Users should upgrade to Log4j 2 as it addresses numerous other issues from the previous versions.
How severe is CVE-2021-4104?
CVE-2021-4104 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with high attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-4104 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 81% (100th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-4104?
CVE-2021-4104 primarily affects Apache Log4j. In total, 72 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-4104?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-4104 published?
CVE-2021-4104 was published on 2021-12-14 and last updated on 2026-06-17.

References

Affected products (72)

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