CVE-2021-45105
Apache Log4j2 does not always protect from infinite recursion in lookup evaluation
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
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.
Official description from the CVE record, published by apache. Copyright © 1999-2026 The MITRE Corporation. See /security/cve/legal for the CVE license. View the record on cve.org
Key data
CVSS 3.1 Medium 5.9
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack vector: Network
The vulnerable component can be reached over a network, possibly from the Internet.
Attack complexity: High
The attack depends on conditions outside the attacker's control, so it takes preparation.
Privileges required: None
No account or privileges are needed.
User interaction: None
No action from any user is needed.
Scope: Unchanged
The impact stays within the vulnerable component.
Confidentiality impact: None
No effect on the secrecy of data.
Integrity impact: None
No effect on the trustworthiness of data.
Availability impact: High
Serious or total effect on availability.
| Metric | Value | What it means |
|---|---|---|
| Attack vector | Network | The vulnerable component can be reached over a network, possibly from the Internet. |
| Attack complexity | High | The attack depends on conditions outside the attacker's control, so it takes preparation. |
| Privileges required | None | No account or privileges are needed. |
| User interaction | None | No action from any user is needed. |
| Scope | Unchanged | The impact stays within the vulnerable component. |
| Confidentiality impact | None | No effect on the secrecy of data. |
| Integrity impact | None | No effect on the trustworthiness of data. |
| Availability impact | High | Serious or total effect on availability. |
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EPSS
- Score
- 0.99999 (99.99% probability)
- Percentile
- 99.99%
- Scores of
- Nov 10, 2026
- Model
- v2026.06.15
CISA assessment as of May 29, 2026
- Automatable
- no
- Technical impact
- partial
Weakness (CWE)
Affected products
Apache Log4j2
- affected: log4j-core up to before 2.17.0
References
- logging.apache.org/log4j/2.x/security.html
- psirt.global.sonicwall.com/vuln-detail/SNWLID-2021-0032
- VU#930724 (kb.cert.org)third-party-advisory
- 20211210 Vulnerabilities in Apache Log4j Library Affecting Cisco Products: December 2021 (tools.cisco.com)vendor-advisory
- [oss-security] 20211218 CVE-2021-45105: Apache Log4j2 does not always protect from infinite recursion in lookup evaluation (openwall.com)mailing-list
- DSA-5024 (debian.org)vendor-advisory
- cert-portal.siemens.com/productcert/pdf/ssa-479842.pdf
- security.netapp.com/advisory/ntap-20211218-0001
- zerodayinitiative.com/advisories/ZDI-21-1541
- cert-portal.siemens.com/productcert/pdf/ssa-501673.pdf
- oracle.com/security-alerts/cpujan2022.html
- oracle.com/security-alerts/cpuapr2022.html
- oracle.com/security-alerts/cpujul2022.html
Timeline
- ID reserved
- Record published
- Record last updated
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Data from the CVE Program (MITRE), CISA KEV and FIRST EPSS. CVSS is owned by FIRST and used by permission. Not affiliated with or endorsed by MITRE, CISA or FIRST. Data as of Nov 10, 2026, 19:52 UTC. Sources and licenses