CVE-2019-19768
Description
A use-after-free vulnerability was found in the Linux kernel’s implementation of blktrace in the __blk_add_trace function. A local attacker with permissions to run block trace instructions against a device can create a situation where the core block_trace object is used after it is freed. The attacker can pre-groom memory to race this use-after-free to create a condition where the memory is corrupted and cause privilege escalation.
The ability to create this condition requires elevated privileges, and it has been decided that this change in Red Hat Enterprise Linux 5 and 6 would risk introducing possible regressions and will not be backported.
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 | 6.7 | 7.5 | N/A |
| Attack Vector | Local | Network | N/A |
| Attack Complexity | Low | Low | N/A |
| Privileges Required | High | None | N/A |
| User Interaction | None | None | N/A |
| Scope | Unchanged | Unchanged | N/A |
| Confidentiality | High | None | N/A |
| Integrity Impact | High | None | N/A |
| Availability Impact | High | High | N/A |
Vector
Red Hat: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
NVD: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Red Hat CVSS v3 Score Explanation
The use-after-free looks to be able to be used shortly after in relay_reserve . The parameters to this can be attacker-controlled and then further allow for arbitrary memory writes via memcpy. Issuing working block trace requests against block devices require permissions to do so, which are not standard user permissions.
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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