Exploitalert - Database of Exploits

Linux Kernel XFRM Privilege Escalation

CVE	Category	Price	Severity
CVE-2017-7184	CWE-264	$10,000	High

Author	Risk	Exploitation Type	Date
Qualys	High	Local	2017-11-24

CVSS	EPSS	EPSSP
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H	0.02192	0.50148

CVSS vector description

Metric	Value	Metric Description	Value Description
Attack vector	Local	AV	The vulnerable system is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Either: the attacker exploits the vulnerability by accessing the target system locally (e.g., keyboard, console), or through terminal emulation (e.g., SSH); or the attacker relies on User Interaction by another person to perform actions required to exploit the vulnerability (e.g., using social engineering techniques to trick a legitimate user into opening a malicious document).
Attack Complexity	Low	AC	The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Privileges Required	Low	PR	The attacker requires privileges that provide basic capabilities that are typically limited to settings and resources owned by a single low-privileged user. Alternatively, an attacker with Low privileges has the ability to access only non-sensitive resources.
User Interaction	None	UI	The vulnerable system can be exploited without interaction from any human user, other than the attacker. Examples include: a remote attacker is able to send packets to a target system a locally authenticated attacker executes code to elevate privileges
Scope		S	An exploited vulnerability can affect resources beyond the security scope managed by the security authority that is managing the vulnerable component. This is often referred to as a 'privilege escalation,' where the attacker can use the exploited vulnerability to gain control of resources that were not intended or authorized.
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.

https://cxsecurity.com/ascii/WLB-2017110137

Linux Kernel XFRM Privilege Escalation

SSD Advisory Linux Kernel XFRM Privilege Escalation Full report: https://blogs.securiteam.com/index.php/archives/3535 Twitter: @SecuriTeam_SSD Weibo: SecuriTeam_SSD Vulnerability Summary The following advisory describes a Use-after-free vulnerability found in Linux kernel that can lead to privilege escalation. The vulnerability found in Netlink socket subsystem XFRM. Netlink is used to transfer information between the kernel and user-space processes. It consists of a standard sockets-based interface for user space processes and an internal kernel API for kernel modules. Credit An independent security researcher, Mohamed Ghannam, has reported this vulnerability to Beyond Securitys SecuriTeam Secure Disclosure program Vendor response The vulnerability has been addressed as part of 1137b5e (ipsec: Fix aborted xfrm policy dump crash) Vulnerability details An unprivileged user can change Netlink socket subsystem XFRM value sk->sk_rcvbuf (sk == struct sock object). The value can be changed into specific range via setsockopt(SO_RCVBUF). sk_rcvbuf is the total number of bytes of a buffer receiving data via recvmsg/recv/read. The sk_rcvbuf value is how many bytes the kernel should allocate for the skb (struct sk_buff objects). skb->trusize is a variable which keep track of how many bytes of memory are consumed, in order to not wasting and manage memory, the kernel can handle the skb size at run time. For example, if we allocate a large socket buffer (skb) and we only received 1-byte packet size, the kernel will adjust this by calling skb_set_owner_r. By calling skb_set_owner_r the sk->sk_rmem_alloc (refers to an atomic variable sk->sk_backlog.rmem_alloc) is modified. When we create a XFRM netlink socket, xfrm_dump_policy is called, when we close the socket xfrm_dump_policy_done is called. xfrm_dump_policy_done is called whenever cb_running for netlink_sock object is true. The xfrm_dump_policy_done tries to clean-up a xfrm walk entry which is managed by netlink_callback object. When netlink_skb_set_owner_r is called (like skb_set_owner_r) it updates the sk_rmem_alloc. netlink_dump(): In above snippet we can see that netlink_dump() check fails when sk->sk_rcvbuf is smaller than sk_rmem_alloc (notice that we can control sk->sk_rcvbuf via stockpot). When this condition fails, it jumps to the end of a function and quit with failure and the value of cb_running doesnt changed to false. nlk->cb_running is true, thus xfrm_dump_policy_done() is being called. nlk->cb.done points to xfrm_dump_policy_done, it worth noting that this function handles a doubly linked list, so if we can tweak this vulnerability to reference a controlled buffer, we could have a read/write what/where primitive. -- Thanks Maor Shwartz Beyond Security GPG Key ID: 6D273779F52A9FC2

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