CVE-2015-4700
Description
A flaw was found in the kernel's implementation of the Berkeley Packet Filter (BPF). A local attacker could craft BPF code to crash the system by creating a situation in which the JIT compiler would fail to correctly optimize the JIT image on the last pass. This would lead to the CPU executing instructions that were not part of the JIT code.
Statement
This issue does not affect the Linux kernels as shipped with Red Hat Enterprise Linux 5 and 6 as it does not contain the affected code. This does not affect the Red Hat Enterprise MRG 2 as it does not enable the affected code at compile time.
This issue affects the Linux kernels as shipped with Red Hat Enterprise Linux 7.
Mitigation
This issue does not affect most systems by default. An administrator would need to have enabled the BPF JIT to be affected.
It can be disabled immediately with the command:
# echo 0 > /proc/sys/net/core/bpf_jit_enable
Or it can be disabled for all subsequent boots of the system by setting a value in /etc/sysctl.d/44-bpf-jit-disable
## start file ##
net.core.bpf_jit_enable=0
## end file ##
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 v2 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.2 | 4.9 | N/A |
| Attack Vector | Local | Local | N/A |
| Access Complexity | Low | Low | N/A |
| Authentication | None | None | N/A |
| Confidentiality Impact | Complete | None | N/A |
| Integrity Impact | Complete | None | N/A |
| Availability Impact | Complete | Complete | N/A |
Vector
Red Hat: AV:L/AC:L/Au:N/C:C/I:C/A:C
NVD: AV:L/AC:L/Au:N/C:N/I:N/A:C
Understanding the Weakness (CWE)
Confidentiality
Technical Impact: Read Memory; Read Application Data
When reusing a resource such as memory or a program variable, the original contents of that resource may not be cleared before it is sent to an untrusted party.
Access Control
Technical Impact: Bypass Protection Mechanism
If security-critical decisions rely on a variable having a "0" or equivalent value, and the programming language performs this initialization on behalf of the programmer, then a bypass of security may occur.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
The uninitialized data may contain values that cause program flow to change in ways that the programmer did not intend. For example, if an uninitialized variable is used as an array index in C, then its previous contents may produce an index that is outside the range of the array, possibly causing a crash or an exit in other environments.
Acknowledgements
Red Hat would like to thank Daniel Borkmann for reporting this issue.
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