Infinite recursion in Apache Log4j



Published: 2021-12-18 | Updated: 2021-12-23
Risk Medium
Patch available YES
Number of vulnerabilities 1
CVE-ID CVE-2021-45105
CWE-ID CWE-835
Exploitation vector Network
Public exploit Public exploit code for vulnerability #1 is available.
Vulnerable software
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Apache Log4j
Universal components / Libraries / Libraries used by multiple products

Vendor Apache Foundation

Security Bulletin

This security bulletin contains one medium risk vulnerability.

1) Infinite loop

EUVDB-ID: #VU59051

Risk: Medium

CVSSv3.1: 6.7 [CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:P/RL:O/RC:C]

CVE-ID: CVE-2021-45105

CWE-ID: CWE-835 - Loop with Unreachable Exit Condition ('Infinite Loop')

Exploit availability: Yes

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


CPE2.3 External links

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

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.



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