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CVE-2016-4558 : Detail

CVE-2016-4558

7
/
HIGH
0.06%V3
Local
2016-05-23 08:00 +00:00
2016-07-25 14:57 +00:00
CVE.org
NVD

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Descriptions

The BPF subsystem in the Linux kernel before 4.5.5 mishandles reference counts, which allows local users to cause a denial of service (use-after-free) or possibly have unspecified other impact via a crafted application on (1) a system with more than 32 Gb of memory, related to the program reference count or (2) a 1 Tb system, related to the map reference count.

Informations

Metrics

Metric Score Severity CVSS Vector Source
V3.1 7 HIGH CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

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.

High

successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected.

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 6.9 AV:L/AC:M/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 : 39773

Publication date : 2016-05-03 22:00 +00:00
Author : Google Security Research
EDB Verified : Yes

Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=809 Most things in the kernel use 32-bit reference counters, relying on the fact that the memory constraints of real computers make it impossible to create enough references to overflow the counters. There are exceptions for things like `struct file` because it is possible to create references to them with relatively little memory usage. Using BPF_MAP_TYPE_PROG_ARRAY maps, it is possible to create references to BPF programs that only need sizeof(void*) bytes each (8 bytes on amd64), permitting an overflow after filling ~32GB of memory that is subject to RLIMIT_MEMLOCK restrictions. The requirement for more than 32GB of RAM is relatively high, but not impossible. The requirement that the allocations need to be below RLIMIT_MEMLOCK is probably the bigger obstacle for exploitation: On most Linux systems, every user is only permitted to allocate up to 64KiB of RAM. However: - There are systems where RLIMIT_MEMLOCK is disabled administratively. - On systems with containers (e.g. LXC containers), usually every container's root user has access to 2^16 different UIDs. If an attacker has control over 9 containers and can share file descriptors between them or has control over one container with a relatively high number of mapped UIDs, he should be able to trigger the overflow. The attached PoC, when run in a Ubuntu 16.04 VM with 40GB RAM and the RLIMIT_MEMLOCK limit disabled, needs 25 minutes to execute and causes the following oops: [ 1850.676543] BUG: unable to handle kernel paging request at ffffc900069c5010 [ 1850.676550] IP: [<ffffffff81173525>] bpf_prog_put_rcu+0x5/0x30 [ 1850.676556] PGD 9bc094067 PUD 9bc095067 PMD 9b4d2b067 PTE 0 [ 1850.676558] Oops: 0000 [#1] SMP [ 1850.676561] Modules linked in: nls_utf8 isofs vboxsf(OE) snd_intel8x0 snd_ac97_codec ac97_bus snd_pcm snd_seq_midi snd_seq_midi_event joydev snd_rawmidi snd_seq snd_seq_device snd_timer input_leds snd serio_raw soundcore vboxvideo(OE) 8250_fintek drm i2c_piix4 vboxguest(OE) mac_hid parport_pc ppdev lp parport autofs4 hid_generic usbhid hid psmouse ahci libahci fjes video e1000 pata_acpi [ 1850.676579] CPU: 0 PID: 1861 Comm: overflow Tainted: G OE 4.4.0-21-generic #37-Ubuntu [ 1850.676581] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006 [ 1850.676582] task: ffff8809b2fe4b00 ti: ffff8809b2f3c000 task.ti: ffff8809b2f3c000 [ 1850.676583] RIP: 0010:[<ffffffff81173525>] [<ffffffff81173525>] bpf_prog_put_rcu+0x5/0x30 [ 1850.676585] RSP: 0018:ffff8809b2f3fdb8 EFLAGS: 00010286 [ 1850.676586] RAX: ffffffff81a24f20 RBX: 0000000000000000 RCX: 0000000000000001 [ 1850.676587] RDX: ffff880230ebc110 RSI: ffff880230ebc100 RDI: ffffc900069c5000 [ 1850.676588] RBP: ffff8809b2f3fdc0 R08: 0000000000000000 R09: 0000000000000000 [ 1850.676589] R10: ffff8809b55468e0 R11: ffff880230ebc110 R12: ffffc90814ce6060 [ 1850.676590] R13: ffffc90814ce6000 R14: ffff8809b5a9d1a0 R15: ffff8809b29cf480 [ 1850.676592] FS: 00007fbe54cf5700(0000) GS:ffff8809e3c00000(0000) knlGS:0000000000000000 [ 1850.676593] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b [ 1850.676594] CR2: ffffc900069c5010 CR3: 00000009ae9ce000 CR4: 00000000000006f0 [ 1850.676598] Stack: [ 1850.676599] ffffffff8117810e ffff8809b2f3fde8 ffffffff811783c6 ffffc90814ce6000 [ 1850.676600] 0000000000000008 ffff8809b55468e0 ffff8809b2f3fdf8 ffffffff811729bd [ 1850.676602] ffff8809b2f3fe10 ffffffff811733b9 ffff880230ebc100 ffff8809b2f3fe58 [ 1850.676603] Call Trace: [ 1850.676607] [<ffffffff8117810e>] ? prog_fd_array_put_ptr+0xe/0x10 [ 1850.676609] [<ffffffff811783c6>] bpf_fd_array_map_clear+0x36/0x50 [ 1850.676611] [<ffffffff811729bd>] bpf_map_put_uref+0x1d/0x20 [ 1850.676612] [<ffffffff811733b9>] bpf_map_release+0x19/0x30 [ 1850.676616] [<ffffffff8120e514>] __fput+0xe4/0x220 [ 1850.676617] [<ffffffff8120e68e>] ____fput+0xe/0x10 [ 1850.676621] [<ffffffff8109e943>] task_work_run+0x73/0x90 [ 1850.676625] [<ffffffff81083ba4>] do_exit+0x2e4/0xae0 [ 1850.676626] [<ffffffff81084423>] do_group_exit+0x43/0xb0 [ 1850.676628] [<ffffffff810844a4>] SyS_exit_group+0x14/0x20 [ 1850.676632] [<ffffffff818244f2>] entry_SYSCALL_64_fastpath+0x16/0x71 [ 1850.676633] Code: cf 00 55 48 89 e5 48 89 78 08 48 89 07 48 c7 47 08 60 55 e6 81 48 89 3d 4a 20 cf 00 5d c3 0f 1f 84 00 00 00 00 00 66 66 66 66 90 <48> 8b 47 10 3e ff 08 74 01 c3 55 48 8b 7f 10 48 c7 c6 20 2f 17 [ 1850.676649] RIP [<ffffffff81173525>] bpf_prog_put_rcu+0x5/0x30 [ 1850.676650] RSP <ffff8809b2f3fdb8> [ 1850.676651] CR2: ffffc900069c5010 [ 1850.676653] ---[ end trace 90333448b9273067 ]--- [ 1850.676655] Fixing recursive fault but reboot is needed! I believe that this issue illustrates that reference count hardening makes sense, even without reference leaks. A suggested patch (compile-tested) is attached. Fixed in https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/kernel/bpf?id=92117d8443bc5afacc8d5ba82e541946310f106e Proof of Concept: https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/39773.zip

Products Mentioned

Configuraton 0

Linux>>Linux_kernel >> Version From (including) 4.4 To (excluding) 4.4.11

Linux>>Linux_kernel >> Version From (including) 4.5 To (excluding) 4.5.5

Configuraton 0

Canonical>>Ubuntu_linux >> Version 14.04

Canonical>>Ubuntu_linux >> Version 16.04

References

http://www.ubuntu.com/usn/USN-3006-1
Tags : vendor-advisory, x_refsource_UBUNTU
http://www.ubuntu.com/usn/USN-3005-1
Tags : vendor-advisory, x_refsource_UBUNTU
http://www.ubuntu.com/usn/USN-3007-1
Tags : vendor-advisory, x_refsource_UBUNTU
http://www.openwall.com/lists/oss-security/2016/05/06/4
Tags : mailing-list, x_refsource_MLIST

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