CVE-2018-17182 Detail

CVE-2018-17182

Score / Severity

7.8

High

CVE Descriptions

An issue was discovered in the Linux kernel through 4.18.8. The vmacache_flush_all function in mm/vmacache.c mishandles sequence number overflows. An attacker can trigger a use-after-free (and possibly gain privileges) via certain thread creation, map, unmap, invalidation, and dereference operations.

CVE Informations

Related Weaknesses

CWE-ID	Weakness Name	Source
CWE-416	Use After Free The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.

Metrics

Metrics	Score	Severity	CVSS Vector	Source
V3.1	7.8	HIGH	CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H More informations Base: Exploitabilty Metrics The Exploitability metrics reflect the characteristics of the thing that is vulnerable, which we refer to formally as the vulnerable component. Attack Vector This metric reflects the context by which vulnerability exploitation is possible. Local The vulnerable component is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Attack Complexity This metric describes the conditions beyond the attacker’s control that must exist in order to exploit the vulnerability. Low Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success when attacking the vulnerable component. Privileges Required This metric describes the level of privileges an attacker must possess before successfully exploiting the vulnerability. Low The attacker requires privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges has the ability to access only non-sensitive resources. User Interaction This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable component. None The vulnerable system can be exploited without interaction from any user. Base: Scope Metrics The Scope metric captures whether a vulnerability in one vulnerable component impacts resources in components beyond its security scope. Scope Formally, a security authority is a mechanism (e.g., an application, an operating system, firmware, a sandbox environment) that defines and enforces access control in terms of how certain subjects/actors (e.g., human users, processes) can access certain restricted objects/resources (e.g., files, CPU, memory) in a controlled manner. All the subjects and objects under the jurisdiction of a single security authority are considered to be under one security scope. If a vulnerability in a vulnerable component can affect a component which is in a different security scope than the vulnerable component, a Scope change occurs. Intuitively, whenever the impact of a vulnerability breaches a security/trust boundary and impacts components outside the security scope in which vulnerable component resides, a Scope change occurs. Unchanged An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority. Base: Impact Metrics The Impact metrics capture the effects of a successfully exploited vulnerability on the component that suffers the worst outcome that is most directly and predictably associated with the attack. Analysts should constrain impacts to a reasonable, final outcome which they are confident an attacker is able to achieve. Confidentiality Impact This metric measures the impact to the confidentiality of the information resources managed by a software component due to a successfully exploited vulnerability. High There is a total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact. For example, an attacker steals the administrator's password, or private encryption keys of a web server. Integrity Impact This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. High There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component. Availability Impact This metric measures the impact to the availability of the impacted component resulting from a successfully exploited vulnerability. High There is a total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable). Temporal Metrics The Temporal metrics measure the current state of exploit techniques or code availability, the existence of any patches or workarounds, or the confidence in the description of a vulnerability. Environmental Metrics These metrics enable the analyst to customize the CVSS score depending on the importance of the affected IT asset to a user’s organization, measured in terms of Confidentiality, Integrity, and Availability.	[email protected]
V2	7.2		AV:L/AC:L/Au:N/C:C/I:C/A:C	[email protected]

EPSS

EPSS is a scoring model that predicts the likelihood of a vulnerability being exploited.

EPSS Score

The EPSS model produces a probability score between 0 and 1 (0 and 100%). The higher the score, the greater the probability that a vulnerability will be exploited.

EPSS Percentile

The percentile is used to rank CVE according to their EPSS score. For example, a CVE in the 95th percentile according to its EPSS score is more likely to be exploited than 95% of other CVE. Thus, the percentile is used to compare the EPSS score of a CVE with that of other CVE.

EPSS First.org

Exploit information

Exploit Database EDB-ID : 45497

Publication date : 2018-09-25 22h00 +00:00
Author : Google Security Research
EDB Verified : Yes

Since commit 615d6e8756c8 ("mm: per-thread vma caching", first in 3.15), Linux has per-task VMA caches that contain up to four VMA pointers for fast lookup. VMA caches are invalidated by bumping the 32-bit per-mm sequence number mm->vmacache_seqnum; when the sequence number wraps, vmacache_flush_all() scans through all running tasks and wipes the VMA caches of all tasks that share current's mm. In commit 6b4ebc3a9078 ("mm,vmacache: optimize overflow system-wide flushing", first in 3.16), a bogus fastpath was added that skips the invalidation on overflow if current->mm->mm_users==1. This means that the following sequence of events triggers a use-after-free: [A starts as a singlethreaded process] A: create mappings X and Y (in separate memory areas far away from other allocations) A: perform repeated invalidations until current->mm->vmacache_seqnum==0xffffffff and current->vmacache.seqnum==0xfffffffe A: dereference an address in mapping Y that is not paged in (thereby populating A's VMA cache with Y at seqnum 0xffffffff) A: unmap mapping X (thereby bumping current->mm->vmacache_seqnum to 0) A: without any more find_vma() calls (which could happen e.g. via pagefaults), create a thread B B: perform repeated invalidations until current->mm->vmacache_seqnum==0xfffffffe B: unmap mapping Y (thereby bumping current->mm->vmacache_seqnum to 0xffffffff) A: dereference an address in the freed mapping Y (or any address that isn't present in the pagetables and doesn't correspond to a valid VMA cache entry) A's VMA cache is still at sequence number 0xffffffff from before the overflow. The sequence number has wrapped around in the meantime, back to 0xffffffff, and A's outdated VMA cache is considered to be valid. I am attaching the following reproduction files: vmacache-debugging.patch: Kernel patch that adds some extra logging for VMA cache internals. vma_test.c: Reproducer code dmesg: dmesg output of running the reproducer in a VM In a Debian 9 VM, I've tested the reproducer against a 4.19.0-rc3+ kernel with vmacache-debugging.patch applied, configured with CONFIG_DEBUG_VM_VMACACHE=y. Usage: user@debian:~/vma_bug$ gcc -O2 -o vma_test vma_test.c -g && ./vma_test Segmentation fault Within around 40 minutes, I get the following warning in dmesg: ============================================= [ 2376.292518] WARNING: CPU: 0 PID: 1103 at mm/vmacache.c:157 vmacache_find+0xbb/0xd0 [ 2376.296813] Modules linked in: btrfs xor zstd_compress raid6_pq [ 2376.300095] CPU: 0 PID: 1103 Comm: vma_test Not tainted 4.19.0-rc3+ #161 [ 2376.303650] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014 [ 2376.305796] RIP: 0010:vmacache_find+0xbb/0xd0 [ 2376.306963] Code: 48 85 c0 74 11 48 39 78 40 75 1f 48 39 30 77 06 48 39 70 08 77 19 83 c2 01 83 fa 04 41 0f 44 d1 83 e9 01 75 c7 31 c0 c3 f3 c3 <0f> 0b 31 c0 c3 65 48 ff 05 98 97 9b 6a c3 90 90 90 90 90 90 90 0f [ 2376.311881] RSP: 0000:ffffa934c1e3bec0 EFLAGS: 00010283 [ 2376.313258] RAX: ffff8ac7eaf997d0 RBX: 0000133700204000 RCX: 0000000000000004 [ 2376.315165] RDX: 0000000000000001 RSI: 0000133700204000 RDI: ffff8ac7f3820dc0 [ 2376.316998] RBP: ffff8ac7f3820dc0 R08: 0000000000000001 R09: 0000000000000000 [ 2376.318789] R10: 0000000000000000 R11: 0000000000000000 R12: ffffa934c1e3bf58 [ 2376.320590] R13: ffff8ac7f3820dc0 R14: 0000000000000055 R15: ffff8ac7e9355140 [ 2376.322481] FS: 00007f96165ca700(0000) GS:ffff8ac7f3c00000(0000) knlGS:0000000000000000 [ 2376.324620] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 2376.326101] CR2: 0000133700204000 CR3: 0000000229d28001 CR4: 00000000003606f0 [ 2376.327906] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 2376.329819] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 2376.331571] Call Trace: [ 2376.332208] find_vma+0x16/0x70 [ 2376.332991] ? vfs_read+0x10f/0x130 [ 2376.333852] __do_page_fault+0x191/0x470 [ 2376.334816] ? async_page_fault+0x8/0x30 [ 2376.335776] async_page_fault+0x1e/0x30 [ 2376.336746] RIP: 0033:0x555e2a2b4c37 [ 2376.337600] Code: 05 80 e8 9c fc ff ff 83 f8 ff 0f 84 ad 00 00 00 8b 3d 81 14 20 00 e8 48 02 00 00 48 b8 00 40 20 00 37 13 00 00 bf 37 13 37 13 <c6> 00 01 31 c0 e8 cf fc ff ff 48 83 ec 80 31 c0 5b 5d 41 5c c3 48 [ 2376.342085] RSP: 002b:00007ffd505e8d30 EFLAGS: 00010206 [ 2376.343334] RAX: 0000133700204000 RBX: 0000000100000000 RCX: 00007f9616102700 [ 2376.345133] RDX: 0000000000000008 RSI: 00007ffd505e8d18 RDI: 0000000013371337 [ 2376.346834] RBP: 00007f96165e4000 R08: 0000000000000000 R09: 0000000000000000 [ 2376.348889] R10: 0000000000000001 R11: 0000000000000246 R12: 0000000100000000 [ 2376.350570] R13: 00007ffd505e8ea0 R14: 0000000000000000 R15: 0000000000000000 [ 2376.352246] ---[ end trace 995fa641c5115cfb ]--- [ 2376.353406] vma_test[1103]: segfault at 133700204000 ip 0000555e2a2b4c37 sp 00007ffd505e8d30 error 6 in vma_test[555e2a2b4000+2000] ============================================= The source code corresponding to the warning, which is triggered because the VMA cache references a VMA struct that has been reallocated to another process in the meantime: #ifdef CONFIG_DEBUG_VM_VMACACHE if (WARN_ON_ONCE(vma->vm_mm != mm)) break; #endif ################################################################################ Attaching an ugly exploit for Ubuntu 18.04, kernel linux-image-4.15.0-34-generic at version 4.15.0-34.37. It takes about an hour to run before popping a root shell. Usage: First compile with ./compile.sh, then run ./puppeteer. Example run: user@ubuntu-18-04-vm:~/vmacache$ ./puppeteer Do Sep 20 23:55:11 CEST 2018 puppeteer: old kmsg consumed got map from child! got WARNING got RSP line: 0xffff9e0bc2263c60 got RAX line: 0xffff8c7caf1d61a0 got RDI line: 0xffff8c7c214c7380 reached WARNING part 2 got R8 line: 0xffffffffa7243680 trace consumed offset: 0x110 fake vma pushed suid file detected, launching rootshell... we have root privs now... Fr Sep 21 00:48:00 CEST 2018 root@ubuntu-18-04-vm:~/vmacache# Proof of Concept: https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/45497.zip