CVE-2020-25705
Description
A flaw in the way reply ICMP packets are limited in the Linux kernel functionality was found that allows to quickly scan open UDP ports. This flaw allows an off-path remote user to effectively bypassing source port UDP randomization. The highest threat from this vulnerability is to confidentiality and possibly integrity, because software that relies on UDP source port randomization are indirectly affected as well.
Statement
This issue is rated as having Moderate impact because of the attack scenario limitation. It is possible to harm the networking services only, but not for the overall system under attack, and impossible to get access to this remote system under attack.
Mitigation
The mitigation is to disable ICMP destination unreachable messages.
The commands to disable UDP port unreachable ICMP reply messages:
iptables -I OUTPUT -p icmp --icmp-type destination-unreachable -j DROP
service iptables save
For additional information about "service iptables save" please read https://access.redhat.com/solutions/1597703
It is not recommended to apply this rule if host being used as forwarder (router) of IP packets.
Or it is possible to use this firewall-cmd instead of iptables and the result is similar:
firewall-cmd --permanent --direct --add-rule ipv4 filter OUTPUT 0 -p icmp --icmp-type destination-unreachable -j DROP
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 | 7.4 | 7.4 | N/A |
| Attack Vector | Network | Network | N/A |
| Attack Complexity | High | High | N/A |
| Privileges Required | None | None | N/A |
| User Interaction | None | None | N/A |
| Scope | Unchanged | Unchanged | N/A |
| Confidentiality | High | High | N/A |
| Integrity Impact | High | High | N/A |
| Availability Impact | None | None | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
NVD: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
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