CVE-2020-25705

Public on

Last Modified: UTC

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.

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.

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

Additional information

  • Bugzilla 1894579: kernel: ICMP rate limiting can be used for DNS poisoning attack
  • CWE-330: Use of Insufficiently Random Values
  • FAQ: Frequently asked questions about CVE-2020-25705

Common Vulnerability Scoring System (CVSS) Score Details

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 HatNVD

CVSS v3 Base Score

7.4

7.4

Attack Vector

Network

Network

Attack Complexity

High

High

Privileges Required

None

None

User Interaction

None

None

Scope

Unchanged

Unchanged

Confidentiality Impact

High

High

Integrity Impact

High

High

Availability Impact

None

None

CVSS v3 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

Frequently Asked Questions

Why is Red Hat's CVSS v3 score or Impact different from other vendors?

My product is listed as "Under investigation" or "Affected", when will Red Hat release a fix for this vulnerability?

What can I do if my product is listed as "Will not fix"?

What can I do if my product is listed as "Fix deferred"?

What is a mitigation?

I have a Red Hat product but it is not in the above list, is it affected?

Why is my security scanner reporting my product as vulnerable to this vulnerability even though my product version is fixed or not affected?

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