CVE-2026-54886
MediumCVSS 4.3Exploitation Probability (EPSS)
Low risk25th percentile - higher than 25% of all known CVEs
Summary
An infinite loop vulnerability in the ssh_sftpd module of Erlang/OTP SSH allows an authenticated SFTP user to permanently block an SFTP channel. By sending extended data (SSH_MSG_CHANNEL_EXTENDED_DATA) with a non-zero type code, the attacker causes the handle_data/4 function to loop indefinitely, preventing further message processing on that channel.
Risk Assessment
The risk is a Denial of Service (DoS) attack on the SFTP server by an authenticated user. The attack can cause CPU degradation and memory growth, especially with multiple channels opened, but does not allow file access or credential theft.
Recommendation
Immediately upgrade Erlang/OTP to version 29.0.3, 28.5.0.3, or 27.3.4.14, depending on the branch used. Additionally, consider limiting the maximum number of channels (max_channels) in the SSH configuration to reduce the potential impact of the attack.
Other vulnerabilities in Erlang/OTP SSH
See all- CVE-2026-53422Medium
A vulnerability in the ssh_sftpd module of the SSH server in OTP (Erlang) allows an authenticated SFTP user to enumerate the existence of files and directories outside the configured root directory. The issue stems from improper path handling in the SSH_FXP_REALPATH handler, which does not canonicalize the path before checking restrictions.
- CVE-2026-48859Medium
Erlang/OTP ssh (ssh_auth, ssh_options modules) has an observable timing discrepancy vulnerability. With user_passwords or password option enabled, password checking for valid usernames takes ~300ms, while for invalid ones ~0ms, allowing unauthenticated remote username enumeration.
- CVE-2026-32147Medium
A Path Traversal vulnerability in the ssh_sftpd module of Erlang OTP ssh allows an authenticated SFTP user to modify file attributes outside the configured chroot directory.
Original NVD description (English source)
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 before OTP 29.0.3, OTP 28.5.0.3 and OTP 27.3.4.14, corresponding to ssh from 3.0.1 before 6.0.2, 5.5.2.2 and 5.2.11.9.