CVE-2017-8779
Description
It was found that due to the way rpcbind uses libtirpc (libntirpc), a memory leak can occur when parsing specially crafted XDR messages. An attacker sending thousands of messages to rpcbind could cause its memory usage to grow without bound, eventually causing it to be terminated by the OOM killer.
Statement
In the default system configuration, with the sysctl variable vm.overcommit_memory set to either 0 (the default) or 1, an attack would take a not-insignificant amount of time to exhaust the system's memory. If vm.overcommit_memory is set to a value of 2, the time required to exhaust system memory is sufficiently reduced. It was further noticed that, a 32-bit system would have its memory exhausted faster than a 64-bit system.
Mitigation
rpcbind should be protected by iptables so that only trusted hosts that require access can reach it (eg, nfs clients). Applying per-IP rate limits in iptables will also significantly limit the impact of this attack. The default iptables rules in the system-config-firewall or firewalld package deny all remote access to rpcbind.
If you elect to run your system with overcommit turned off, daemons should have memory limits enforced by the init system to ensure stability. With systemd, use directives such as LimitAS in unit files. With upstart, place ulimit commands in /etc/sysconfig/$daemon.
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 | 7.5 | 7.5 | N/A |
| Attack Vector | Network | Network | N/A |
| Attack Complexity | Low | Low | N/A |
| Privileges Required | None | None | N/A |
| User Interaction | None | None | N/A |
| Scope | Unchanged | Unchanged | N/A |
| Confidentiality | None | None | N/A |
| Integrity Impact | None | None | N/A |
| Availability Impact | High | High | N/A |
Vector
Red Hat: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Crash, Exit, or Restart; DoS: Resource Consumption (CPU); DoS: Resource Consumption (Memory); DoS: Resource Consumption (Other)
If an attacker can trigger the allocation of the limited resources, but the number or size of the resources is not controlled, then the most common result is denial of service. This would prevent valid users from accessing the product, and it could potentially have an impact on the surrounding environment, i.e., the product may slow down, crash due to unhandled errors, or lock out legitimate users. For example, a memory exhaustion attack against an application could slow down the application as well as its host operating system.
Access Control,Other
Technical Impact: Bypass Protection Mechanism; Other
In some cases it may be possible to force the product to "fail open" in the event of resource exhaustion. The state of the product -- and possibly the security functionality - may then be compromised.
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