CVE-2021-45105Network attack vector

Process termination via self-referential Context Lookups

Published Dec 18, 2021 · Updated May 29, 2026

Uncontrolled recursion in Apache Log4j 2 allows remote attackers to terminate affected Java processes via crafted Thread Context data. In log4j-core, lookup substitution repeatedly re-expands a self-referential value from the Thread Context Map until the Java stack overflows. Reachability requires a non-default PatternLayout Context Lookup and attacker control of the referenced MDC value; the bounded consequence is process termination.

CVSS severity5.9
Medium
EPSS probability100.00%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Uncontrolled recursion in Apache Log4j 2 allows remote attackers to terminate affected Java processes via crafted Thread Context data. In log4j-core, lookup substitution repeatedly re-expands a self-referential value from the Thread Context Map until the Java stack overflows. Reachability requires a non-default PatternLayout Context Lookup and attacker control of the referenced MDC value; the bounded consequence is process termination.

The record

CVE
CVE-2021-45105
Published
Dec 18, 2021
Updated
May 29, 2026
Vendor
Apache Software Foundation
Product
Apache Log4j 2
Classifications
CWE-674, CWE-20, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 18, 2021CVE publishedPublication date reported by the CVE source.
  2. May 29, 2026Record 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=log4j-core <2.17.0 changes=[{"at":"2.13.0","status":"affected"},{"at":"2.12.3","status":"unaffected"},{"at":"2.4","status":"affected"},{"at":"2.3.1","status":"unaffected"},{"at":"2.0-alpha1","status":"affected"}]

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Apache Software Foundation · Apache Log4j 2version=log4j-core <2.17.0 changes=[{"at":"2.13.0","status":"affected"},{"at":"2.12.3","status":"unaffected"},{"at":"2.4","status":"affected"},{"at":"2.3.1","status":"unaffected"},{"at":"2.0-alpha1","status":"affected"}]

Published CVSS scores

8.6GitHubCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
5.9Apache Software FoundationCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/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 exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-674Uncontrolled Recursion
CWE-20Improper Input Validation
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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

Technologies

Your stack

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Your stack

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