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Distribution-over-TLS LAN Allowlist is Silently Bypassed

High
IngelaAndin published GHSA-gp7x-mfv6-52cv Jun 10, 2026

Package

OTP

Affected versions

>= 26.0

Patched versions

29.0.2, 28.5.0.2, 27.3.4.13
ssl (OTP)
>= 11.0
11.7.2, 11.6.0.2,11.2.12.9

Description

Impact

Erlang distribution over TLS run with the kernel 'check_ip' flag to enforce connecting nodes to be on the same LAN
are impacted by this CVE.

The check_ip/1 function in lib/ssl/src/inet_tls_dist.erl (line 723) calls inet:sockname(Socket) to obtain the peer IP address instead of the correct inet:peername(Socket). This means both IP and PeerIP are always identical (both are the local address), so the LAN subnet mask comparison always passes. The undocumented check_ip operational safeguard — intended to restrict distribution connections to the local subnet — is completely ineffective for TLS distribution.The check_ip/1 function in lib/ssl/src/inet_tls_dist.erl (line 723) calls inet:sockname(Socket) to obtain the peer IP address instead of the correct inet:peername(Socket). This means both IP and PeerIP are always identical (both are the local address), so the LAN subnet mask comparison always passes. The undocumented check_ip operational safeguard — intended to restrict distribution connections to the local subnet — is completely ineffective for TLS distribution.

3.2 The Bug

check_ip(Socket) ->
    case application:get_env(check_ip) of
        {ok, true} ->
            maybe
                {ok, {IP, _}} ?= inet:sockname(Socket),       %% line 717: correct (local IP)
                ...
                {ok, Netmask} ?= find_netmask(IP, Ifaddrs),
                {ok, {PeerIP, _}} ?= inet:sockname(Socket),   %% line 723: BUG! should be peername
                ...
                mask(IP, Netmask) =:= mask(PeerIP, Netmask)   %% always true (IP == PeerIP)
                    orelse {false, PeerIP}
            ...
    end.

Since IP and PeerIP are both obtained from inet:sockname/1, they are always identical. The subnet mask comparison mask(IP, Netmask) =:= mask(PeerIP, Netmask) is trivially true for every connection.

3.3 Correct Implementation (kernel)

Both inet_tcp_dist.erl and inet_epmd_dist.erl correctly use inet:peername(Socket) to obtain the peer IP:

%% inet_epmd_dist.erl line 129
{ok, {PeerIp, _} = PeerAddress} ?= inet:peername(Socket),
check_ip(Ip, PeerIp),
```### 3.2 The Bug

```erlang
check_ip(Socket) ->
    case application:get_env(check_ip) of
        {ok, true} ->
            maybe
                {ok, {IP, _}} ?= inet:sockname(Socket),       %% line 717: correct (local IP)
                ...
                {ok, Netmask} ?= find_netmask(IP, Ifaddrs),
                {ok, {PeerIP, _}} ?= inet:sockname(Socket),   %% line 723: BUG! should be peername
                ...
                mask(IP, Netmask) =:= mask(PeerIP, Netmask)   %% always true (IP == PeerIP)
                    orelse {false, PeerIP}
            ...
    end.

Since IP and PeerIP are both obtained from inet:sockname/1, they are always identical. The subnet mask comparison mask(IP, Netmask) =:= mask(PeerIP, Netmask) is trivially true for every connection.

3.3 Correct Implementation (kernel)

Both inet_tcp_dist.erl and inet_epmd_dist.erl correctly use inet:peername(Socket) to obtain the peer IP:

%% inet_epmd_dist.erl line 129
{ok, {PeerIp, _} = PeerAddress} ?= inet:peername(Socket),
check_ip(Ip, PeerIp),

3.4 Trigger Conditions

For exploitation, all of the following must hold:

  1. Erlang distribution is configured to use TLS (-proto_dist inet_tls)
  2. Kernel env check_ip is set to true
  3. The cluster's TLS verification accepts certificates not exclusively issued to cluster members — i.e., the CA is shared with other services (web servers, VPN, other teams). If the cluster uses a dedicated CA that only signs cluster node certificates, then certificate verification alone already restricts access and check_ip adds no value even when working correctly.
  4. Attacker holds a valid certificate signed by that same CA (either legitimately — e.g., they run another service — or via compromise of a non-cluster certificate holder)

Workarounds

Implement ssl option verify_fun that performed the check correctly.

Affected/Unaffected Versions

A version larger than or equal to one of the listed patched versions is unaffected; otherwise, a version that satisfies an expression listed under affected versions is affected, and if it does not, it is unaffected.

The documentation of the OTP version scheme describes how versions should be compared. Note that versions used prior to OTP 17.0, when the new OTP version scheme was introduced, are never listed since it is not well defined how to compare those versions.

The vulnerability was introduced in OTP 26.0 (ssl 11.0). OTP versions before 26.0 does not implement this feature.

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Adjacent
Attack Complexity High
Attack Requirements Present
Privileges Required Low
User interaction None
Vulnerable System Impact Metrics
Confidentiality High
Integrity High
Availability High
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:A/AC:H/AT:P/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

CVE ID

CVE-2026-48860

Weaknesses

Incorrect Authorization

The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check. Learn more on MITRE.

Comparison Using Wrong Factors

The code performs a comparison between two entities, but the comparison examines the wrong factors or characteristics of the entities, which can lead to incorrect results and resultant weaknesses. Learn more on MITRE.

Credits