Upstream information
Description
Loop with Unreachable Exit Condition ('Infinite Loop') vulnerability in Erlang OTP ssh (ssh_sftpd module) allows an authenticated SFTP user to render an SFTP channel permanently unresponsive.The handle_data/4 function in ssh_sftpd contains a catch-all clause that accepts channel data of any type. When channel data with a non-zero type code (SSH_MSG_CHANNEL_EXTENDED_DATA) arrives with an empty pending buffer and a payload at or below the SFTP packet size limit, the clause tail-calls itself with identical arguments, creating an infinite loop.
The SFTP protocol operates exclusively on normal channel data (type 0). Extended data (non-zero type) is meaningless for SFTP and is never sent by conforming clients. However, the SSH protocol permits any channel participant to send extended data on an open channel, so an authenticated SFTP client can trigger the loop by sending SSH_MSG_CHANNEL_EXTENDED_DATA with any data_type_code and any non-empty payload at or below the size limit.
The targeted ssh_sftpd process enters an infinite tail-recursive loop. It never processes another message, its message queue grows without bound, and it can only be stopped by killing the process. BEAM's reduction-based scheduler preemption continues to function, so other processes on the node are not starved, but each stuck channel process consumes its full CPU time share continuously and accumulates unbounded message queue memory. Opening many channels amplifies the CPU and memory impact.
Erlang/OTP SSH configurations using the default max_channels setting (infinity) allow an authenticated user to open unlimited channels per connection, amplifying the attack without requiring multiple TCP connections or authentications.
No file contents, credentials, or write access are obtainable through this issue. The impact is limited to denial of service on targeted SFTP channels, with secondary CPU degradation and memory growth.
This vulnerability is associated with program file lib/ssh/src/ssh_sftpd.erl and program routine ssh_sftpd:handle_data/4.
This issue affects OTP from OTP 17.0 until OTP 29.0.3, 28.5.0.3, and 27.3.4.14 corresponding to ssh from 3.0.1 until 6.0.2, 5.5.2.2, and 5.2.11.9.
SUSE information
Overall state of this security issue: Pending
This issue is currently rated as having moderate severity.
| CVSS detail | SUSE |
|---|---|
| Base Score | 6.5 |
| Vector | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H |
| Attack Vector | Network |
| Attack Complexity | Low |
| Privileges Required | Low |
| User Interaction | None |
| Scope | Unchanged |
| Confidentiality Impact | None |
| Integrity Impact | None |
| Availability Impact | High |
| CVSSv3 Version | 3.1 |
| CVSS detail | CNA (6b3ad84c-e1a6-4bf7-a703-f496b71e49db) | SUSE |
|---|---|---|
| Base Score | 5.3 | 7.1 |
| Vector | CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X | CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N |
| Attack Vector | Network | Network |
| Attack Complexity | Low | Low |
| Attack Requirements | None | None |
| Privileges Required | Low | Low |
| User Interaction | None | None |
| Vulnerable System Confidentiality Impact | None | None |
| Vulnerable System Integrity Impact | None | None |
| Vulnerable System Availability Impact | Low | High |
| Subsequent System Confidentiality Impact | None | None |
| Subsequent System Integrity Impact | None | None |
| Subsequent System Availability Impact | None | None |
| CVSSv4 Version | 4.0 | 4.0 |
Status of this issue by product and package
Please note that this evaluation state might be work in progress, incomplete or outdated. Also information for service packs in the LTSS phase is only included for issues meeting the LTSS criteria. If in doubt, feel free to contact us for clarification. The updates are grouped by state of their lifecycle. SUSE product lifecycles are documented on the lifecycle page.
| Product(s) | Source package | State |
|---|---|---|
| Products under general support and receiving all security fixes. | ||
| SUSE Linux Enterprise High Performance Computing 15 SP7 | erlang | Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP7 | erlang26 | Affected |
| SUSE Linux Enterprise Module for Server Applications 15 SP7 | erlang | Affected |
| SUSE Linux Enterprise Module for Server Applications 15 SP7 | erlang26 | Affected |
| SUSE Linux Enterprise Server 15 SP7 | erlang | Affected |
| SUSE Linux Enterprise Server 15 SP7 | erlang26 | Affected |
| SUSE Linux Enterprise Server 16.0 | erlang | Affected |
| SUSE Linux Enterprise Server 16.1 | erlang | Affected |
| SUSE Linux Enterprise Server for SAP Applications 15 SP7 | erlang | Affected |
| SUSE Linux Enterprise Server for SAP Applications 15 SP7 | erlang26 | Affected |
| SUSE Linux Enterprise Server for SAP applications 16.0 | erlang | Affected |
| SUSE Linux Enterprise Server for SAP applications 16.1 | erlang | Affected |
| openSUSE Leap 16.0 | erlang | Affected |
| Products under Long Term Service Pack support and receiving important and critical security fixes. | ||
| SUSE Linux Enterprise High Performance Computing 15 SP4 | erlang | Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS | erlang | Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP5 | erlang | Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP5-LTSS | erlang | Affected |
| SUSE Linux Enterprise Module for Server Applications 15 SP4 | erlang | Affected |
| SUSE Linux Enterprise Module for Server Applications 15 SP5 | erlang | Affected |
| SUSE Linux Enterprise Module for Server Applications 15 SP6 | erlang | Affected |
| SUSE Linux Enterprise Module for Server Applications 15 SP6 | erlang26 | Affected |
| SUSE Linux Enterprise Server 15 SP4 | erlang | Affected |
| SUSE Linux Enterprise Server 15 SP4-LTSS | erlang | Affected |
| SUSE Linux Enterprise Server 15 SP5 | erlang | Affected |
| SUSE Linux Enterprise Server 15 SP5-LTSS | erlang | Affected |
| SUSE Linux Enterprise Server 15 SP6 | erlang | Affected |
| SUSE Linux Enterprise Server 15 SP6 | erlang26 | Affected |
| SUSE Linux Enterprise Server 15 SP6-LTSS | erlang | Affected |
| SUSE Linux Enterprise Server 15 SP6-LTSS | erlang26 | Affected |
| SUSE Linux Enterprise Server for SAP Applications 15 SP6 | erlang | Affected |
| SUSE Linux Enterprise Server for SAP Applications 15 SP6 | erlang26 | Affected |
| SUSE Manager Proxy 4.3 | erlang | Affected |
| SUSE Manager Proxy LTS 4.3 | erlang | Affected |
| SUSE Manager Retail Branch Server 4.3 | erlang | Affected |
| SUSE Manager Retail Branch Server LTS 4.3 | erlang | Affected |
| SUSE Manager Server 4.3 | erlang | Affected |
| SUSE Manager Server LTS 4.3 | erlang | Affected |
| Products past their end of life and not receiving proactive updates anymore. | ||
| SUSE Enterprise Storage 7 | erlang | Affected |
| SUSE Enterprise Storage 7.1 | erlang | Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP2 | erlang | Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP2-ESPOS | erlang | Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP2-LTSS | erlang | Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP3 | erlang | Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP3-ESPOS | erlang | Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP3-LTSS | erlang | Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS | erlang | Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP5-ESPOS | erlang | Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP6 | erlang | Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP6 | erlang26 | Affected |
| SUSE Linux Enterprise Module for Server Applications 15 SP2 | erlang | Affected |
| SUSE Linux Enterprise Module for Server Applications 15 SP3 | erlang | Affected |
| SUSE Linux Enterprise Real Time 15 SP2 | erlang | Affected |
| SUSE Linux Enterprise Real Time 15 SP3 | erlang | Affected |
| SUSE Linux Enterprise Real Time 15 SP4 | erlang | Affected |
| SUSE Linux Enterprise Server 15 SP2 | erlang | Affected |
| SUSE Linux Enterprise Server 15 SP2-BCL | erlang | Affected |
| SUSE Linux Enterprise Server 15 SP2-LTSS | erlang | Affected |
| SUSE Linux Enterprise Server 15 SP3 | erlang | Affected |
| SUSE Linux Enterprise Server 15 SP3-BCL | erlang | Affected |
| SUSE Linux Enterprise Server 15 SP3-LTSS | erlang | Affected |
| SUSE Linux Enterprise Server for SAP Applications 15 SP2 | erlang | Affected |
| SUSE Linux Enterprise Server for SAP Applications 15 SP3 | erlang | Affected |
| SUSE Linux Enterprise Server for SAP Applications 15 SP4 | erlang | Affected |
| SUSE Linux Enterprise Server for SAP Applications 15 SP5 | erlang | Affected |
| SUSE Manager Proxy 4.1 | erlang | Affected |
| SUSE Manager Proxy 4.2 | erlang | Affected |
| SUSE Manager Retail Branch Server 4.1 | erlang | Affected |
| SUSE Manager Retail Branch Server 4.2 | erlang | Affected |
| SUSE Manager Server 4.1 | erlang | Affected |
| SUSE Manager Server 4.2 | erlang | Affected |
| openSUSE Leap 15.3 | erlang | Affected |
| openSUSE Leap 15.4 | erlang | Affected |
| openSUSE Leap 15.5 | erlang | Affected |
| openSUSE Leap 15.6 | erlang | Affected |
| openSUSE Leap 15.6 | erlang26 | Affected |
SUSE Timeline for this CVE
CVE page created: Thu Jul 2 20:05:24 2026CVE page last modified: Fri Jul 3 13:54:55 2026