CVE-2019-11487
Description
A flaw was found in the Linux kernel's implementation of the FUSE filesystem, where it allows a page reference counter overflow. If a page reference counter overflows into a negative value, it can be placed back into the "free" list for reuse by other applications. This flaw allows a local attacker who can manipulate memory page reference counters to cause memory corruption and possible privilege escalation by triggering a use-after-free condition.
The current attack requires the system to have approximately 140 GB of RAM for this attack to be performed. It may be possible that the attack can occur with fewer memory requirements.
Mitigation
Preventing loading of the 'fuse' kernel module will prevent attackers from using this exploit against the system; howeve the functionality of being able to access the filesystems that would be allowed by fuse would no longer be allowed . See “How do I blacklist a kernel module to prevent it from loading automatically?" ( https://access.redhat.com/solutions/41278) for instructions on how to disable the 'fuse' kernel module from autoloading. This mitigation may not be suitable if access to the functionality provided by fuse is required.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.8 | 7.8 | N/A |
| Attack Vector | Local | Local | N/A |
| Attack Complexity | High | Low | N/A |
| Privileges Required | Low | Low | N/A |
| User Interaction | None | None | N/A |
| Scope | Changed | Unchanged | N/A |
| Confidentiality | High | High | N/A |
| Integrity Impact | High | High | N/A |
| Availability Impact | High | High | N/A |
Vector
Red Hat: CVSS:3.0/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H
NVD: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Understanding the Weakness (CWE)
Integrity
Technical Impact: Modify Memory
The use of previously freed memory may corrupt valid data, if the memory area in question has been allocated and used properly elsewhere.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
If chunk consolidation occurs after the use of previously freed data, the process may crash when invalid data is used as chunk information.
Confidentiality
Technical Impact: Read Memory
Read operations on freed memory can sometimes leak sensitive information instead of causing a crash
Integrity,Confidentiality,Availability
Technical Impact: Execute Unauthorized Code or Commands
If malicious data is entered before chunk consolidation can take place, it may be possible to take advantage of a write-what-where primitive to execute arbitrary code. If the newly allocated data happens to hold a class, in C++ for example, various function pointers may be scattered within the heap data. If one of these function pointers is overwritten with an address to valid shellcode, execution of arbitrary code can be achieved.
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