12月9日晚,互联网上公开了Apache log4j2的一个严重级别的远程代码执行漏洞。由于Apache log4j2某些功能存在递归解析功能,攻击者可直接构造恶意请求触发远程代码执行漏洞,而无需特殊配置。Apache Struts2、Apache Solr、Apache Druid、Apache Flink等均受此漏洞影响。鉴于该框架应用范围极广,且漏洞利用代码已在互联网上公开,请各单位及时采取有效防护措施,防止安全事件发生。
一、漏洞描述
Apache log4j2是一款优秀的Java日志框架。该日志框架被大量用于业务系统开发时记录日志信息。大多数情况下,开发者可能会将用户输入导致的错误信息写入日志中。但由于Apache log4j2中的某些功能允许进行递归解析,攻击者可以构造恶意代码,触发错误并将恶意代码作为错误信息写入日志,进而利用递归解析执行。该漏洞对当前几乎全部的Apache log4j2版本生效,且无需系统进行任何特殊配置,威胁性极高。
二、漏洞影响版本
Apache Log4j 2.x < 2.15.0-rc2
三、检测方法与修复建议
检测方法
排查Java应用是否存在引入log4j-api、log4j-core的情况。若存在引入,则大概率存在漏洞。漏洞本地验证POC参考地址如下:
https://github.com/tangxiaofeng7/apache-log4j-poc
修复建议
1.及时更新补丁。在漏洞曝出后,Apache官方公开了修复补丁2.15.0-rc1,但该补丁只修复了ldap利用方式,未修复rmi利用方式,不可用;后续官方再次公开修复补丁2.15.0-rc2,修复后目前无直接利用方式,但疑似未完全完成修复。采用此方法进行修复时,请后续跟进官方的相应更新进展。
补丁下载地址:
https://github.com/apache/logging-log4j2/releases/tag/log4j-2.15.0-rc2
2.在因故不能更新版本的情况下,需采用各种临时防护措施进行加固:
(1)修改jvm参数 -Dlog4j2.formatMsgNoLookups=true
(2)在应用classpath下添加 log4j2.component.properties 配置文件,其内容为log4j2.formatMsgNoLookups=true
(3)将系统环境变量
FORMAT_MESSAGES_PATTERN_DISABLE_LOOKUPS
设置为true
3.该漏洞公开的验证脚本中,均以dnslog.cn等部分dnslog平台作为命令执行情况验证。对于非许可范围内的访问情况提高风险防控意识。部分公共dnslog平台域名列举如下:
ceye.io
dnslog.link
dnslog.cn
dnslog.io
tu4.org
awvsscan119.autoverify.cn
burpcollaborator.net
s0x.cn
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