From: SecuriTeam <support@securiteam.com.>
To: list@securiteam.com
Date: 7 Jun 2006 10:25:46 +0200
Subject: [UNIX] Linux Kernel NetFilter DoS
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Linux Kernel NetFilter DoS
------------------------------------------------------------------------
SUMMARY
Improper handling of memory with Linux SNMP allows attackers to crash
NetFilter.
DETAILS
Vulnerable Systems:
* Linux kernel version 2.6.16.17 and prior
Immune Systems:
* Linux Kernel version 2.6.16.18
The corruption can be triggered remotely when the ip_nat_snmp_basic module
is loaded and traffic on port 161 or 162 is NATed.
The vulnerability will happen when:
* When snmp_trap_decode fails before the id and address are allocated,
the pointers contain random memory, but are freed by the caller
(snmp_parse_mangle).
* When snmp_trap_decode fails after allocating just the ID, it tries to
free both address and ID, but the address pointer still contains random
memory. The caller frees both ID and random memory again.
* When snmp_trap_decode fails after allocating both, it frees both, and
the callers frees both again.
Vulnerable Code:
--- net/ipv4/netfilter/ip_nat_snmp_basic.c+ net/ipv4/netfilter/ip_nat_snmp_basic.c
@@ -1000,12 +1000,12 @@ static unsigned char snmp_trap_decode(st
return 1;
+err_addr_free:
+ kfree((unsigned long *)trap->ip_address);
+
err_id_free:
kfree(trap->id);
-err_addr_free:
- kfree((unsigned long *)trap->ip_address);
-
return 0;
}
@@ -1123,11 +1123,10 @@ static int snmp_parse_mangle(unsigned ch
struct snmp_v1_trap trap;
unsigned char ret = snmp_trap_decode(&ctx, &trap, map, check);
- /* Discard trap allocations regardless */
- kfree(trap.id);
- kfree((unsigned long *)trap.ip_address);
-
- if (!ret)
+ if (ret) {
+ kfree(trap.id);
+ kfree((unsigned long *)trap.ip_address);
+ } else
return ret;
} else {
Vendor Status:
The vendor has issued a fix in Kernel 2.6.16.18
CVE Information:
<http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2006-2444>;
CVE-2006-2444
ADDITIONAL INFORMATION
The information has been provided by <mailto:alex@ecl-labs.org.> ECL Labs.
The original article can be found at: <http://ecl-labs.org/>;
http://ecl-labs.org/
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