Skip to content

FTP Client PASV Response IP not Validated Against Control Peer, Enabling SSRF and FTP Bounce Attacks

Moderate
IngelaAndin published GHSA-24cv-hwgr-37fq Jun 10, 2026

Package

OTP

Affected versions

>= 17.4

Patched versions

29.0.2, 28.5.0.2, 27.3.4.13
ftp (otp)
>= 1.0
1.2.6, 1.2.4.1, 1.2.3.1
inets (otp)
>= 5.10.4
7.0

Description

Impact

The ftp OTP application provides an FTP client. It is deprecated and scheduled for removal in OTP-30.

ftp_internal:handle_command/3 supports two passive-mode data connection paths depending on the ftp_extension option. The ftp_extension=true path (EPSV) correctly derives the data connection IP from the control socket peer address via peername(CSock), ignoring the server-supplied value. The ftp_extension=false path (PASV, lines 1505-1531) parses the IP directly from the server's 227 response and passes it to gen_tcp:connect/4 without any validation against the control connection peer address.

The default configuration uses the vulnerable path: mode=passive, ipfamily=inet, and ftp_extension=false are all defaults.

A malicious or compromised FTP server can include an arbitrary IP address and port in its 227 response, causing the client to open its data connection to that target instead of back to the server. On ftp:ls/1,2, ftp:nlist/1,2, and ftp:recv/2,3 operations, data read from the redirected target is returned to the caller. On ftp:send/2,3 and ftp:append/2,3 operations, the file content is written to the redirected target. This enables server-side request forgery (SSRF) against internal hosts, cloud metadata endpoints, or other services reachable from the FTP client host, as well as FTP bounce attacks against third-party hosts.

RFC 2577 (FTP Security Considerations, 1999) section 3 explicitly recommends that clients verify the IP address in a PASV response matches the control connection peer. The EPSV handlers in the same module implement this correctly.

Workarounds

  • Pass {ftp_extension, true} to ftp:open/2 to use EPSV instead of PASV. EPSV does not include an IP in the server response and is not affected.
  • Pass {mode, active} to ftp:open/2 to use active mode, where the client listens and the server connects back.
  • Pass {ipfamily, inet6} to ftp:open/2 to force IPv6, which also selects the EPSV path.

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 17.4 (inets 5.10.4). In OTP 21.0 the ftp client was split out of inets into a standalone ftp OTP application (ftp 1.0). OTP versions before 17.4 are not affected.

Credits

Thanks to Jonatan Männchen for finding and responsibly disclosing this vulnerability to the Erlang/OTP project.

Severity

Moderate

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 Network
Attack Complexity Low
Attack Requirements Present
Privileges Required None
User interaction None
Vulnerable System Impact Metrics
Confidentiality Low
Integrity Low
Availability None
Subsequent System Impact Metrics
Confidentiality Low
Integrity Low
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:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N

CVE ID

CVE-2026-48858

Weaknesses

Server-Side Request Forgery (SSRF)

The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination. Learn more on MITRE.

Credits