Faiblesses connexes
| CWE-ID |
Nom de la faiblesse |
Source |
| CWE-787 |
Out-of-bounds Write
The product writes data past the end, or before the beginning, of the intended buffer. |
|
Métriques
| Métriques |
Score |
Gravité |
CVSS Vecteur |
Source |
| V3.0 |
7.8 |
HIGH |
CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Base: Exploitabilty MetricsThe 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. A vulnerability exploitable with Local access means that the vulnerable component is not bound to the network stack, and the attacker's path is via read/write/execute capabilities. In some cases, the attacker may be logged in locally in order to exploit the vulnerability, otherwise, she may rely on User Interaction to execute a malicious file. Attack Complexity This metric describes the conditions beyond the attacker's control that must exist in order to exploit the vulnerability. Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component. Privileges Required This metric describes the level of privileges an attacker must possess before successfully exploiting the vulnerability. The attacker is authorized with (i.e. 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 may have the ability to cause an impact only to non-sensitive resources. User Interaction This metric captures the requirement for a user, other than the attacker, to participate in the successful compromise of the vulnerable component. The vulnerable system can be exploited without interaction from any user. Base: Scope MetricsAn important property captured by CVSS v3.0 is the ability for a vulnerability in one software component to impact resources beyond its means, or privileges. Scope Formally, Scope refers to the collection of privileges defined by a computing authority (e.g. an application, an operating system, or a sandbox environment) when granting access to computing resources (e.g. files, CPU, memory, etc). These privileges are assigned based on some method of identification and authorization. In some cases, the authorization may be simple or loosely controlled based upon predefined rules or standards. For example, in the case of Ethernet traffic sent to a network switch, the switch accepts traffic that arrives on its ports and is an authority that controls the traffic flow to other switch ports. An exploited vulnerability can only affect resources managed by the same authority. In this case the vulnerable component and the impacted component are the same. Base: Impact MetricsThe Impact metrics refer to the properties of the impacted component. 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. There is 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. 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. There is 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 MetricsThe Temporal metrics measure the current state of exploit techniques or code availability, the existence of any patches or workarounds, or the confidence that one has in the description of a vulnerability. Environmental Metrics
|
[email protected] |
| V2 |
7.2 |
|
AV:L/AC:L/Au:N/C:C/I:C/A:C |
[email protected] |
EPSS
EPSS est un modèle de notation qui prédit la probabilité qu'une vulnérabilité soit exploitée.
Score EPSS
Le modèle EPSS produit un score de probabilité compris entre 0 et 1 (0 et 100 %). Plus la note est élevée, plus la probabilité qu'une vulnérabilité soit exploitée est grande.
Percentile EPSS
Le percentile est utilisé pour classer les CVE en fonction de leur score EPSS. Par exemple, une CVE dans le 95e percentile selon son score EPSS est plus susceptible d'être exploitée que 95 % des autres CVE. Ainsi, le percentile sert à comparer le score EPSS d'une CVE par rapport à d'autres CVE.
Informations sur l'Exploit
Exploit Database EDB-ID : 43464
Date de publication : 2018-01-07 23h00 +00:00
Auteur : Google Security Research
EDB Vérifié : Yes
The MemoryIntArray class allows processes to share an in-memory array of integers backed by an "ashmem" file descriptor. As the class implements the Parcelable interface, it can be inserted into a Parcel, and optionally placed in a Bundle and transferred via binder to remote processes.
Instead of directly tracking the size of the shared memory region, the MemoryIntArray class calls the ASHMEM_GET_SIZE ioctl on the ashmem descriptor to retrieve it on-demand. Previously, the code made a single call to ASHMEM_GET_SIZE in order to retrieve the region's size, both before mapping it, and before unmapping it. Since the region's size could be set via ASHMEM_SET_SIZE until the region has been mapped, this opened the possibility for race conditions where an attacker alters the size in-between the first size retrieval and the mapping operation.
This issue has since been addressed (CVE-2017-0412), using the following pattern:
(see http://androidxref.com/8.0.0_r4/xref/frameworks/base/core/jni/android_util_MemoryIntArray.cpp#69)
1. int ashmemSize = ashmem_get_size_region(fd);
2. if (ashmemSize <= 0) {
3. jniThrowException(env, "java/io/IOException", "bad ashmem size");
4. return -1;
5. }
6.
7. // IMPORTANT: Ashmem allows the caller to change its size until
8. // it is memory mapped for the first time which lazily creates
9. // the underlying VFS file. So the size we get above may not
10. // reflect the size of the underlying shared memory region. Therefore,
11. // we first memory map to set the size in stone an verify if
12. // the underlying ashmem region has the same size as the one we
13. // memory mapped. This is critical as we use the underlying
14. // ashmem size for boundary checks and memory unmapping.
15. int protMode = owner ? (PROT_READ | PROT_WRITE) : PROT_READ;
16. void* ashmemAddr = mmap(NULL, ashmemSize, protMode, MAP_SHARED, fd, 0);
17. if (ashmemAddr == MAP_FAILED) {
18. jniThrowException(env, "java/io/IOException", "cannot mmap ashmem");
19. return -1;
20. }
21.
22. // Check if the mapped size is the same as the ashmem region.
23. int mmapedSize = ashmem_get_size_region(fd);
24. if (mmapedSize != ashmemSize) {
25. munmap(reinterpret_cast<void *>(ashmemAddr), ashmemSize);
26. jniThrowException(env, "java/io/IOException", "bad file descriptor");
27. return -1;
28. }
As we can see above, the code verifies that the size retrieved prior to mapping and after performing the mapping operation are equal, thus attempting to eliminate the race condition. However, looking at the ashmem driver, the following code is used to implement the ASHMEM_SET_SIZE ioctl:
(see http://androidxref.com/kernel_3.18/xref/drivers/staging/android/ashmem.c#753)
a. case ASHMEM_SET_SIZE:
b. ret = -EINVAL;
c. if (!asma->file) {
d. ret = 0;
e. asma->size = (size_t) arg;
f. }
g. break;
The ioctl does not acquire the "ashmem_mutex" to perform the ioctl itself. Therefore, an "mmap" operation could be in-flight, while the ASHMEM_SET_SIZE ioctl is being processed. This opens up the possibility to the following schedule, triggering a race condition:
[Process A]:
1. Attacker sends a MemoryIntArray with a crafted ashmem file descriptor in a Bundle, and with a small size
[System Server]:
2. Target process (e.g., system_server) unparcels the bundle with the MemoryIntArray, instantiating it
3. This triggers the code path above, executing lines 1-16
[Process A]:
4. Attacker calls ASHMEM_SET_SIZE, either during or before the mmap call
4.1. Lines a-c are executed, asma->file is still NULL
[System Server]:
5. Target process continues executing lines 16-24
5.1. Target process sees the old size, as the ASHMEM_SET_SIZE operation didn't complete yet
5.2. Therefore, the condition at line 24 is not satisfied
[Process A]:
6. Lines d-f are executed, setting the size to a new value
[System Server]:
7. Some time later, target process runs the finalizer, which retrieves the new size, and uses it to munmap the descriptor
7.1. This causes an inter-process munmap with an attacker-controller size
This issue can be exploited similarly to the previous ashmem bugs -- once a larger "munmap" is performed in the target process, it can be used to "free" a data structure such as a thread's stack, allowing the attacker to replace it with their own controlled contents.
While the exploitable condition is present in MemoryIntArray, I believe a fix should also be applied to the kernel to prevent such conditions from occurring in other contexts. Namely, the ashmem driver should acquire the "ashmem_mutex" during the ASHMEM_SET_SIZE operation, in order to guarantee that no races with ongoing "mmap" operations are possible. In addition, MemoryIntArray should not rely on multiple calls to ASHMEM_GET_SIZE, but should rather perform a single ASHMEM_GET_SIZE operation and store the returned size for both the "mmap" and "munmap" operations.
To demonstrate the race condition, I've added a busy loop to the ashmem driver between lines c. and d., increasing the race window to allow for easier demonstration of the schedule above.
I've attached a PoC which triggers this race condition and causes system_server to call munmap on a large memory region. To reproduce the issue, apply the diff in "ashmem_delay.diff" to the ashmem driver, then run the attached program. Doing so should result in a large "munmap" operation in system_server, causing it to crash.
The issue can also be exploited from the "isolated_app" SELinux context (and perhaps from the Chrome sandbox?), as all that's required to leverage the attack is the ability to issue ashmem syscalls, and to interact with the ActivityManager service (which is exposed to "isolated_app").
Proof of Concept:
https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/43464.zip
Products Mentioned
Configuraton 0
Google>>Android >> Version -
Références
