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Antivirus: bypassing SSDT Hooking
Synthesis of the vulnerability
When an antivirus redirects the SSDT to detect viruses, a local attacker can use an atomicity error, in order to bypass this protection.
Impacted products: Avast AV, CA Antivirus, F-Secure AV, AVG AntiVirus, Kaspersky AV, VirusScan, Norton Antivirus, Norton Internet Security, Panda AV, Panda Internet Security, Symantec AV.
Severity of this bulletin: 2/4.
Consequences of an intrusion: administrator access/rights, data flow.
Hacker's origin: user shell.
Number of vulnerabilities in this bulletin: 13.
Creation date: 10/05/2010.
Revision date: 11/05/2010.
Références of this threat: CVE-2010-5151, CVE-2010-5152, CVE-2010-5154, CVE-2010-5156, CVE-2010-5161, CVE-2010-5163, CVE-2010-5166, CVE-2010-5167, CVE-2010-5168, CVE-2010-5171, CVE-2010-5172, CVE-2010-5177, CVE-2010-5179, VIGILANCE-VUL-9633.
Description of the vulnerability
The SSDT table (System Service Descriptor Table) contains references of system calls:
- NtCreateKey : create a key in registry
- NtCreateThread : create a thread
- NtDeleteFile : delete a file
Antiviruses redirect entries of this table to verification functions. Several implementations check parameters, and then call the origin system call. However, between these two operations, a local attacker can change parameters of the system call. A attacker can therefore create a program using legitimate parameters, and then change them just before the system call.
When an antivirus redirects the SSDT to detect viruses, a local attacker can therefore use an atomicity error, in order to bypass this protection.
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