CVE-2024-3661

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Moderate Moderate Impact What does this mean?
7.6 CVSS v3 Base Score

Description

DHCP can add routes to a client’s routing table via the classless static route option (121). VPN-based security solutions that rely on routes to redirect traffic can be forced to leak traffic over the physical interface. An attacker on the same local network can read, disrupt, or possibly modify network traffic expected to be protected by the VPN.

Statement

This vulnerability is also known as TunnelVision and it describes a technique to use DHCP configuration to manipulate hosts to send traffic to an attacker's host instead of through a VPN, as expected. According to MITRE it is reported as a vulnerability against DHCP. However, the DHCP protocol works as intended and as a protocol without cryptographic protection, attackers do not break a security boundary in the DHCP protocol by using the DHCP option 121. To prevent against the attack vector, users or VPN configuration software need to configure the VPN correctly or use other techniques to avoid that a DHCP configuration manipulates routing decisions for packets intended to be contained in the VPN.

This affects only situations where hosts use DHCP in a network and attackers can control a DHCP server. It affects full-tunnel and split-tunnel based VPNs. IPSec policy-based VPNs do not send unencrypted traffic to attackers as they encrypt traffic regardless of the routing decision.

Mitigation

The mitigation steps also ensure that the applications using the VPN cannot access local resources outside the VPN in full-tunnel mode. If access to local resources outside the VPN is needed, additional routing configuration is necessary.

The following steps demonstrate how to configure VPN profiles with NetworkManager to prioritize VPN routes over DHCP routes. This uses routing rules with a higher priority than the rule to lookup the main routing table. This means that the VPN routing table is consulted prior to the main routing table. Please note that a higher priority is configured by setting a lower priority value in the routing configuration.

1. There were two bugs in NetworkManager that prevented these steps from working with profiles using VPN plugins, such as libreswan. Therefore first update NetworkManager:
- On RHEL 8.10, use NetworkManager-1.40.16-18.el8_10 or later.
- On RHEL 9.5 and later, use NetworkManager-1.48.10-5.el9_5 or later.

2. In the next steps, you will assign the VPN routes to a dedicated routing table. By default, RHEL does not use the routing tables 1-252, and you can use one of them. If you configured the system to use some of these tables, identify a free routing table number. The following example uses the routing table 75.

3. Optional: Configure a name for the routing table by adding a line, such as the following, to the /etc/iproute2/rt_tables file:
75 vpn

This makes the output of ip commands easier to understand. Note that NetworkManager only supports using a table ID and not the table name.

4. Configure the VPN connection profile to place the VPN routes in a dedicated routing table:
# nmcli connection modify <VPN_connection_profile> ipv4.route-table <routing_table_number>

For example:
# nmcli connection modify "Company VPN" ipv4.route-table 75

5. Set a low priority value for the table you used in the previous command:
# nmcli connection modify <VPN_connection_profile> ipv4.routing-rules "priority <low_priority_value> from all table <routing_table_number>"

The priority value can be any value between 1 and 32766 but, the lower the value, the higher the priority!

For example:
# nmcli connection modify "Company VPN" ipv4.routing-rules "priority 32345 from all table 75"

6. Reconnect the VPN:
# nmcli connection down <VPN_connection_profile>
# nmcli connection up <VPN_connection_profile>

This only prevents the TunnelVision techniques and possibly related issues regarding IPv4. For IPv6 it might be necessary to repeat the steps for IPv6.
If other software than NetworkManager is used to configure a VPN, it might need similar configuration changes to mitigate against TunnelVision.

Additional Information

External References

Content from www.cve.org is not included.https://www.cve.org/CVERecord?id=CVE-2024-3661

Content from nvd.nist.gov is not included.https://nvd.nist.gov/vuln/detail/CVE-2024-3661

Content from arstechnica.com is not included.https://arstechnica.com/security/2024/05/novel-attack-against-virtually-all-vpn-apps-neuters-their-entire-purpose/

Content from bst.cisco.com is not included.https://bst.cisco.com/quickview/bug/CSCwk05814

Content from datatracker.ietf.org is not included.https://datatracker.ietf.org/doc/html/rfc2131#section-7

Content from datatracker.ietf.org is not included.https://datatracker.ietf.org/doc/html/rfc3442#section-7

Content from fortiguard.fortinet.com is not included.https://fortiguard.fortinet.com/psirt/FG-IR-24-170

Content from issuetracker.google.com is not included.https://issuetracker.google.com/issues/263721377

Content from krebsonsecurity.com is not included.https://krebsonsecurity.com/2024/05/why-your-vpn-may-not-be-as-secure-as-it-claims/

Content from lowendtalk.com is not included.https://lowendtalk.com/discussion/188857/a-rogue-dhcp-server-within-your-network-can-and-will-hijack-your-vpn-traffic

Content from mullvad.net is not included.https://mullvad.net/en/blog/evaluating-the-impact-of-tunnelvision

Content from my.f5.com is not included.https://my.f5.com/manage/s/article/K000139553

Content from news.ycombinator.com is not included.https://news.ycombinator.com/item?id=40279632

Content from news.ycombinator.com is not included.https://news.ycombinator.com/item?id=40284111

Content from security.paloaltonetworks.com is not included.https://security.paloaltonetworks.com/CVE-2024-3661

Content from support.citrix.com is not included.https://support.citrix.com/article/CTX677069/cloud-software-group-security-advisory-for-cve20243661

Content from tunnelvisionbug.com is not included.https://tunnelvisionbug.com/

Content from www.agwa.name is not included.https://www.agwa.name/blog/post/hardening_openvpn_for_def_con

Content from www.leviathansecurity.com is not included.https://www.leviathansecurity.com/research/tunnelvision

Content from www.theregister.com is not included.https://www.theregister.com/2024/05/07/vpn_tunnelvision_dhcp/

Content from www.watchguard.com is not included.https://www.watchguard.com/wgrd-psirt/advisory/wgsa-2024-00009

Content from www.zscaler.com is not included.https://www.zscaler.com/blogs/security-research/cve-2024-3661-k-tunnelvision-exposes-vpn-bypass-vulnerability

Affected Packages and Issued Red Hat Security Errata

Products / Services Components State Errata
Red Hat Enterprise Linux 10 NetworkManager Not affected
Red Hat Enterprise Linux 10 dhcpcd Not affected
Red Hat Enterprise Linux 6 dhcp Not affected
Red Hat Enterprise Linux 6 NetworkManager Will not fix
Red Hat Enterprise Linux 7 dhcp Not affected
Red Hat Enterprise Linux 7 NetworkManager Will not fix
Red Hat Enterprise Linux 8 NetworkManager Fixed RHSA-2025:0288
Red Hat Enterprise Linux 8 dhcp Not affected
Red Hat Enterprise Linux 9 NetworkManager Fixed RHSA-2025:0377
Red Hat Enterprise Linux 9 dhcp Not affected
Unless explicitly stated as not affected, all previous versions of packages in any minor update stream of a product listed here should be assumed vulnerable, although may not have been subject to full analysis.

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 Authorities (CNA) source for its products and services (see Red Hat classifications ).

CVSS v3 Score Breakdown Red Hat NVD
CVSS v3 Base Score 7.6
Attack Vector Adjacent Network
Attack Complexity Low
Privileges Required None
User Interaction None
Scope Unchanged
Confidentiality Impact High
Integrity Impact Low
Availability Impact Low

CVSS v3 Vector

Red Hat CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L

Frequently Asked Questions

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

 For open source software shipped by multiple vendors, the CVSS base scores may vary for each vendor's version depending on the version they ship, how they ship it, the platform, and even how the software is compiled. This makes scoring of vulnerabilities difficult for third-party vulnerability databases such as NVD that only provide a single CVSS base score for each vulnerability. Red Hat scores reflect how a vulnerability affects our products specifically.

For more information, see https://access.redhat.com/solutions/762393.

My product is listed as "Under investigation" or "Affected", when will Red Hat release a fix for this vulnerability?
  • "Under investigation" doesn't necessarily mean that the product is affected by this vulnerability. It only means that our Analysis Team is still working on determining whether the product is affected and how it is affected.
  • "Affected" means that our Analysis Team has determined that this product is affected by this vulnerability and might release a fix to address this in the near future.

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

 A "will not fix" status means that a fix for an affected product version is not planned or not possible due to complexity, which may create additional risk.

Available options depend mostly on the Impact of the vulnerability and the current Life Cycle phase of your product. Overall, you have the following options:
  • Upgrade to a supported product version that includes a fix for this vulnerability (recommended).
  • Apply a mitigation (if one exists).
  • Open a This content is not included.support case to request a prioritization of releasing a fix for this vulnerability.

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

 A deferred status means that a fix for an affected product version is not guaranteed due to higher-priority development work.

Available options depend mostly on the Impact of the vulnerability and the current Life Cycle phase of your product. Overall, you have the following options:
  • Apply a mitigation (if one exists).
  • Open a This content is not included.support case to request a prioritization of releasing a fix for this vulnerability.
  • Red Hat Engineering focuses on addressing high-priority issues based on their complexity or limited lifecycle support. Therefore, lower-priority issues will not receive immediate fixes.

What is a mitigation?

 A mitigation is an action that can be taken to reduce the impact of a security vulnerability, without deploying any fixes.

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

 The listed products were found to include one or more of the components that this vulnerability affects. These products underwent a thorough evaluation to determine their affectedness by this vulnerability. Note that layered products (such as container-based offerings) that consume affected components from any of the products listed in this table may be affected and are not represented.

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

 In order to maintain code stability and compatibility, Red Hat usually does not rebase packages to entirely new versions. Instead, we backport fixes and new features to an older version of the package we distribute. This can result in some security scanners that only consider the package version to report the package as vulnerable. To avoid this, we suggest that you use an approved vulnerability scanner from our This content is not included.Red Hat Vulnerability Scanner Certification program.