Cisco IOS 12.2
Cisco IOS 12.1
Cisco IOS 12.0

描述：

Cisco互联网操作系统（IOS）是Cisco设备所使用的操作系统。

Cisco Systems IOS在解析包含有GRE源路由信息的GRE报文时存在漏洞，远程攻击者可能导致设备处理报文出错。

如果收到了特制的GRE报文的话，IOS设备没有验证偏移字段是否指向报文内，如果偏移值被设置为负值，IOS直接从包含有IP报文全长的整数中减去了偏移，导致缓冲区访问越界溢出。这可能导致将报文环缓冲区（ring buffer）的其他内存内容解释为负载IP报文并以很大的长度信息重新注入到路由队列中：

        GRE decapsulated IP 0.3.74.0->0.0.1.30 (len=65407, ttl=39)
        GRE decapsulated IP 176.94.8.0->0.0.0.0 (len=64904, ttl=0)
        GRE decapsulated IP 0.15.31.193->176.94.8.0 (len=64894, ttl=237)
        GRE decapsulated IP 128.42.131.220->128.0.3.74 (len=64884, ttl=128)

如果能够使用在适当的偏移处包含有IP头的合法通讯精心填充环缓冲区的话，攻击者就可以在IOS中创建有很大长度值的IP报文。

<*来源：FX （fx@phenoelit.de）
  
  链接：http://marc.theaimsgroup.com/?l=bugtraq&m=115756581129301&w=2
        http://www.cisco.com/en/US/tech/tk827/tk369/tsd_technology_security_response09186a008072cd7b.html
*>

测试方法：

Internet Protocol,
                Src Addr: 85.158.1.110 (85.158.1.110),
                Dst Addr: 198.133.219.25 (198.133.219.25)
            Version: 4
            Header length: 20 bytes
            Differentiated Services Field: 0x00
            Total Length: 28
            Identification: 0xaffe (45054)
            Flags: 0x00
            Fragment offset: 0
            Time to live: 30
            Protocol: GRE (0x2f)
            Header checksum: 0xf409 (correct)
            Source: 85.158.1.110 (85.158.1.110)
            Destination: 198.133.219.25 (198.133.219.25)
        Generic Routing Encapsulation (IP)
            Flags and version: 0x4000
                0... .... .... .... = No checksum
                .1.. .... .... .... = Routing
                ..0. .... .... .... = No key
                ...0 .... .... .... = No sequence number
                .... 0... .... .... = No strict source route
                .... .000 .... .... = Recursion control: 0
                .... .... 0000 0... = Flags: 0
                .... .... .... .000 = Version: 0
            Protocol Type: IP (0x0800)
            Checksum: 0x0000
            Offset: 99

建议：

厂商补丁：

Cisco
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目前厂商已经发布了升级补丁以修复这个安全问题，请到厂商的主页下载：

http://www.cisco.com/en/US/tech/tk827/tk369/tsd_technology_security_response09186a008072cd7b.html