#VU59051 Infinite loop in Apache Log4j - CVE-2021-45105

Vulnerability identifier: #VU59051

Vulnerability risk: Medium

CVSSv4.0: 7.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:P/U:Green]

CVE-ID: CVE-2021-45105

CWE-ID: CWE-835

Exploitation vector: Network

Exploit availability: Yes

Vulnerable software:
Apache Log4j
Universal components / Libraries / Libraries used by multiple products

Vendor: Apache Foundation

Description

The vulnerability allows a remote attacker to perform a denial of service (DoS) attack.

The vulnerability exists due to infinite loop within the StrSubstitutor class. A remote attacker can pass specially crafted input to the application, consume all available system resources and cause denial of service conditions.

Payload example: ${${::-${::-$${::-j}}}}

Mitigation
Install updates from vendor's website.

Vulnerable software versions

Apache Log4j: 2.8 - 2.16.0

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External links
https://issues.apache.org/jira/browse/LOG4J2-3230
https://logging.apache.org/log4j/2.x/security.html
https://www.zerodayinitiative.com/advisories/ZDI-21-1541/

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Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability. However, proof of concept for this vulnerability is available.