CVE-2021-45046Known exploitationPublic exploitNetwork attack vector

Remote code execution via recursive Thread Context lookup

Published Dec 14, 2021 · Updated Oct 21, 2025

Expression-language injection in Apache Log4j Core before 2.16.0 allows remote attackers to execute code through crafted Thread Context data. In a non-default Pattern Layout, recursive substitution evaluates attacker-controlled MDC values as Lookup expressions, allowing a JNDI pattern to reach an external naming service. Exploitation requires control of data placed in the Thread Context Map and the vulnerable layout configuration; successful attacks can disclose data or execute code in the application process.

CVSS severity9.0
Critical
EPSS probability99.98%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Expression-language injection in Apache Log4j Core before 2.16.0 allows remote attackers to execute code through crafted Thread Context data. In a non-default Pattern Layout, recursive substitution evaluates attacker-controlled MDC values as Lookup expressions, allowing a JNDI pattern to reach an external naming service. Exploitation requires control of data placed in the Thread Context Map and the vulnerable layout configuration; successful attacks can disclose data or execute code in the application process.

The record

CVE
CVE-2021-45046
Published
Dec 14, 2021
Updated
Oct 21, 2025
Vendor
The Apache Software Foundation
Product
Apache Log4j
Classifications
CWE-917
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 14, 2021CVE publishedPublication date reported by the CVE source.
  2. May 1, 2023Exploitation reportedCISA Known Exploited Vulnerabilities Catalog listing
  3. Oct 21, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=Apache Log4j2 <2.16.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Apache Software Foundation · Apache Log4jversion=Apache Log4j2 <2.16.0

Published CVSS scores

9.0NIST NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H
9.0CISA-ADPCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H
5.1NIST NVDAV:N/AC:H/Au:N/C:P/I:P/A:P
9.0Apache Software FoundationCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationReported
Public exploitPublished

Weakness, pattern, technique

CWE-917Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection')

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Reported exploitation

Technologies

Your stack

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Your stack

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