CVE-2017-7543
Description
A race-condition flaw was discovered in openstack-neutron where, following a minor overcloud update, neutron security groups were disabled. Specifically, the following were reset to 0: net.bridge.bridge-nf-call-ip6tables and net.bridge.bridge-nf-call-iptables. The race was only triggered by an update, at which point an attacker could access exposed tenant VMs and network resources.
Mitigation
To determine whether your system is impacted, run:
$ sudo sysctl net.bridge.bridge-nf-call-ip6tables
$ sudo sysctl net.bridge.bridge-nf-call-iptables
Both should be set to 1
To reset security groups to '1':
1. Apply the following configuration modification:
$ sudo sed -i.back -e 's/reapply_sysctl = 0/reapply_sysctl = 1/' /etc/tuned/tuned-main.conf
2. Ensure the modification was successful:
$ grep reapply_sysctl /etc/tuned/tuned-main.conf
should be "reapply_sysctl = 1"
3. Check whether tuned is running:
$ sudo systemctl status tuned
4. Restart tuned to apply the new configuration:
$ sudo systemctl restart tuned
5. Recheck your security groups and the status of 'reapply_sysctl'.
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 | 5.3 | 5.9 | 5.3 |
| Attack Vector | Network | Network | Network |
| Attack Complexity | High | High | High |
| Privileges Required | None | None | None |
| User Interaction | Required | None | Required |
| Scope | Unchanged | Unchanged | Unchanged |
| Confidentiality | High | High | High |
| Integrity Impact | None | None | None |
| Availability Impact | None | None | None |
Vector
Red Hat: CVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:N/A:N
NVD: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
cve.org: CVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:N/A:N
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Resource Consumption (CPU); DoS: Resource Consumption (Memory); DoS: Resource Consumption (Other)
When a race condition makes it possible to bypass a resource cleanup routine or trigger multiple initialization routines, it may lead to resource exhaustion.
Availability
Technical Impact: DoS: Crash, Exit, or Restart; DoS: Instability
When a race condition allows multiple control flows to access a resource simultaneously, it might lead the product(s) into unexpected states, possibly resulting in a crash.
Confidentiality,Integrity
Technical Impact: Read Files or Directories; Read Application Data
When a race condition is combined with predictable resource names and loose permissions, it may be possible for an attacker to overwrite or access confidential data (CWE-59).
Access Control
Technical Impact: Execute Unauthorized Code or Commands; Gain Privileges or Assume Identity; Bypass Protection Mechanism
This can have security implications when the expected synchronization is in security-critical code, such as recording whether a user is authenticated or modifying important state information that should not be influenced by an outsider.
Acknowledgements
This issue was discovered by Paul Needle (Red Hat).
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