Copyright © 2012 Red Hat, Inc. All rights reserved. Moderate 2026-07-02T16:06:20 erlang: Erlang OTP ssh: Denial of Service via infinite loop in SFTP channel 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H CWE-835

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.

A flaw was found in the Erlang OTP ssh (Secure Shell) component, specifically within its SFTP (SSH File Transfer Protocol) module. An authenticated SFTP user can exploit this vulnerability by sending specially crafted extended data on an open channel. This action triggers an infinite loop in the ssh_sftpd process, rendering the SFTP channel permanently unresponsive and leading to a denial of service (DoS). The affected process will continuously consume CPU resources and accumulate unbounded memory.

A denial-of-service vulnerability was found in the ssh_sftpd module of Erlang/OTP. An authenticated SFTP user can send SSH_MSG_CHANNEL_EXTENDED_DATA messages that trigger an infinite tail-recursive loop in the ssh_sftpd:handle_data/4 function, rendering the targeted SFTP channel permanently unresponsive, with secondary CPU and memory consumption. Set the max_channels daemon option to a finite value instead of the default 'infinity' to limit the number of channels an authenticated user can open per connection, reducing the amplification potential of this vulnerability. Red Hat OpenStack Platform 16.2 Fix deferred erlang Red Hat OpenStack Platform 17.1 Fix deferred erlang Red Hat OpenStack Platform 18.0 Fix deferred erlang https://www.cve.org/CVERecord?id=CVE-2026-54886 https://nvd.nist.gov/vuln/detail/CVE-2026-54886 https://cna.erlef.org/cves/CVE-2026-54886.html https://github.com/erlang/otp/commit/eaf9550b8ad4738b81149d3f617102d980c6dd18 https://github.com/erlang/otp/security/advisories/GHSA-7wp4-pc27-2vj9 https://osv.dev/vulnerability/EEF-CVE-2026-54886 https://www.erlang.org/doc/system/versions.html#order-of-versions